Some minor Tramp changes

[gnu-emacs] / doc / misc / tramp.texi

\input texinfo   @c -*- mode: texinfo; coding: utf-8 -*-
@setfilename ../../info/tramp.info
@c %**start of header
@settitle TRAMP User Manual
@include docstyle.texi
@c %**end of header

@c This is *so* much nicer :)
@footnotestyle end

@c In the Tramp repository, the version number is auto-frobbed from
@c configure.ac, so you should edit that file and run
@c "autoconf && ./configure" to change the version number.

@c Additionally, flags are set with respect to the Emacs flavor; and
@c depending whether Tramp is packaged into (X)Emacs, or standalone.

@include trampver.texi

@c Macro for formatting a file name according to the respective syntax.
@c xxx and yyy are auxiliary macros in order to omit leading and
@c trailing whitespace.  Not very elegant, but I don't know it better.

@c There are subtle differences between texinfo 4.13 and 5.0.  We must
@c declare two versions of the macro.  This will be improved, hopefully.

@c Texinfo 5.0.
@ifset txicommandconditionals
@macro xxx {one}
@set \one\
@end macro

@macro yyy {one, two}
@xxx{x\one\}@c
@ifclear x
\one\@w{}\two\@c
@end ifclear
@clear x\one\
@end macro

@macro trampfn {method, user, host, localname}
@value{prefix}@c
@yyy{\method\,@value{postfixhop}}@c
@yyy{\user\,@@}@c
\host\@value{postfix}\localname\
@end macro
@end ifset

@c Texinfo 4.13.
@ifclear txicommandconditionals
@macro xxx {one}@c
@set \one\@c
@end macro

@macro yyy {one, two}@c
@xxx{x\one\}@c
@ifclear x@c
\one\@w{}\two\@c
@end ifclear
@clear x\one\@c
@end macro

@macro trampfn {method, user, host, localname}@c
@value{prefix}@yyy{\method\,@value{postfixhop}}@yyy{\user\,@@}\host\@value{postfix}\localname\@c
@end macro
@end ifclear

@copying
Copyright @copyright{} 1999--2015 Free Software Foundation, Inc.

@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with the Front-Cover Texts being ``A GNU Manual'',
and with the Back-Cover Texts as in (a) below.  A copy of the license
is included in the section entitled ``GNU Free Documentation License''.

(a) The FSF's Back-Cover Text is: ``You have the freedom to
copy and modify this GNU manual.''
@end quotation
@end copying

@c Entries for @command{install-info} to use
@dircategory @value{emacsname} network features
@direntry
* TRAMP: (tramp).               Transparent Remote Access, Multiple Protocol
                                  @value{emacsname} remote file access via ssh and scp.
@end direntry

@titlepage
@title @value{tramp} version @value{trampver} User Manual
@author by Daniel Pittman
@author based on documentation by Kai Großjohann
@page
@insertcopying
@end titlepage

@contents

@ifnottex
@node Top, Overview, (dir), (dir)
@top @value{tramp} version @value{trampver} User Manual

This file documents @value{tramp} version @value{trampver}, a remote file
editing package for @value{emacsname}.

@value{tramp} stands for ``Transparent Remote (file) Access, Multiple
Protocol''.  This package provides remote file editing, similar to
@value{ftppackagename}.

The difference is that @value{ftppackagename} uses FTP to transfer
files between the local and the remote host, whereas @value{tramp} uses a
combination of @command{rsh} and @command{rcp} or other work-alike
programs, such as @command{ssh}/@command{scp}.

You can find the latest version of this document on the web at
@uref{http://www.gnu.org/software/tramp/}.

@c Pointer to the other Emacs flavor is necessary only in case of
@c standalone installation.
@ifset installchapter
The manual has been generated for @value{emacsname}.
@ifinfo
If you want to read the info pages for @value{emacsothername}, you
should read in @ref{Installation} how to create them.
@end ifinfo
@ifhtml
If you're using the other Emacs flavor, you should read the
@uref{@value{emacsotherfilename}, @value{emacsothername}} pages.
@end ifhtml
@end ifset

@ifhtml
The latest release of @value{tramp} is available for
@uref{ftp://ftp.gnu.org/gnu/tramp/, download}, or you may see
@ref{Obtaining Tramp} for more details, including the Git server
details.

@value{tramp} also has a @uref{http://savannah.gnu.org/projects/tramp/,
Savannah Project Page}.
@end ifhtml

There is a mailing list for @value{tramp}, available at
@email{tramp-devel@@gnu.org}, and archived at
@uref{http://lists.gnu.org/archive/html/tramp-devel/, the
@value{tramp} Mail Archive}.
@ifhtml
Older archives are located at
@uref{http://sourceforge.net/mailarchive/forum.php?forum=tramp-devel,
SourceForge Mail Archive} and
@uref{http://www.mail-archive.com/emacs-rcp@@ls6.cs.uni-dortmund.de/,
The Mail Archive}.
@c in HTML output, there's no new paragraph.
@*@*
@end ifhtml

@insertcopying

@end ifnottex

@menu
* Overview::                    What @value{tramp} can and cannot do.

For the end user:

* Obtaining Tramp::             How to obtain @value{tramp}.
* History::                     History of @value{tramp}.
@ifset installchapter
* Installation::                Installing @value{tramp} with your @value{emacsname}.
@end ifset
* Configuration::               Configuring @value{tramp} for use.
* Usage::                       An overview of the operation of @value{tramp}.
* Bug Reports::                 Reporting Bugs and Problems.
* Frequently Asked Questions::  Questions and answers from the mailing list.

For the developer:

* Files directories and localnames::  How file names, directories and localnames are mangled and managed.
* Traces and Profiles::         How to Customize Traces.
* Issues::                      Debatable Issues and What Was Decided.

* GNU Free Documentation License:: The license for this documentation.
* Function Index::              @value{tramp} functions.
* Variable Index::              User options and variables.
* Concept Index::               An item for each concept.

@detailmenu
 --- The Detailed Node Listing ---
@c
@ifset installchapter
Installing @value{tramp} with your @value{emacsname}

* Installation parameters::     Parameters in order to control installation.
* Load paths::                  How to plug-in @value{tramp} into your environment.

@end ifset

Configuring @value{tramp} for use

* Connection types::            Types of connections made to remote hosts.
* Inline methods::              Inline methods.
* External methods::            External methods.
@ifset emacsgvfs
* GVFS based methods::          GVFS based external methods.
@end ifset
@ifset emacsgw
* Gateway methods::             Gateway methods.
@end ifset
* Default Method::              Selecting a default method.
* Default User::                Selecting a default user.
* Default Host::                Selecting a default host.
* Multi-hops::                  Connecting to a remote host using multiple hops.
* Customizing Methods::         Using Non-Standard Methods.
* Customizing Completion::      Selecting config files for user/host name completion.
* Password handling::           Reusing passwords for several connections.
* Connection caching::          Reusing connection related information.
* Predefined connection information::
                                Setting own connection related information.
* Remote programs::             How @value{tramp} finds and uses programs on the remote host.
* Remote shell setup::          Remote shell setup hints.
* Android shell setup::         Android shell setup hints.
* Auto-save and Backup::        Auto-save and Backup.
* Windows setup hints::         Issues with Cygwin ssh.

Using @value{tramp}

* File name Syntax::            @value{tramp} file name conventions.
* File name completion::        File name completion.
* Ad-hoc multi-hops::           Declaring multiple hops in the file name.
* Remote processes::            Integration with other @value{emacsname} packages.
* Cleanup remote connections::  Cleanup remote connections.

How file names, directories and localnames are mangled and managed

* Localname deconstruction::    Breaking a localname into its components.
@ifset emacs
* External packages::           Integration with external Lisp packages.
@end ifset

@end detailmenu
@end menu


@node Overview
@chapter An overview of @value{tramp}
@cindex overview

After the installation of @value{tramp} into your @value{emacsname}, you
will be able to access files on remote hosts as though they were
local.  Access to the remote file system for editing files, version
control, and @code{dired} are transparently enabled.

Your access to the remote host can be with the @command{rsh},
@command{rlogin}, @command{telnet} programs or with any similar
connection method.  This connection must pass @acronym{ASCII}
successfully to be usable but need not be 8-bit clean.

The package provides support for @command{ssh} connections out of the
box, one of the more common uses of the package.  This allows
relatively secure access to hosts, especially if @command{ftp}
access is disabled.

Under Windows, @value{tramp} is integrated with the PuTTY package,
using the @command{plink} program.

The majority of activity carried out by @value{tramp} requires only that
the remote login is possible and is carried out at the terminal.  In
order to access remote files @value{tramp} needs to transfer their content
to the local host temporarily.

@value{tramp} can transfer files between the hosts in a variety of ways.
The details are easy to select, depending on your needs and the
hosts in question.

The fastest transfer methods for large files rely on a remote file
transfer package such as @command{rcp}, @command{scp}, @command{rsync}
or (under Windows) @command{pscp}.

If the remote copy methods are not suitable for you, @value{tramp} also
supports the use of encoded transfers directly through the shell.
This requires that the @command{mimencode} or @command{uuencode} tools
are available on the remote host.  These methods are generally
faster for small files.

@value{tramp} is still under active development and any problems you encounter,
trivial or major, should be reported to the @value{tramp} developers.
@xref{Bug Reports}.


@subsubheading Behind the scenes
@cindex behind the scenes
@cindex details of operation
@cindex how it works

This section tries to explain what goes on behind the scenes when you
access a remote file through @value{tramp}.

Suppose you type @kbd{C-x C-f} and enter part of an @value{tramp} file name,
then hit @kbd{@key{TAB}} for completion.  Suppose further that this is
the first time that @value{tramp} is invoked for the host in question.  Here's
what happens:

@itemize
@item
@value{tramp} discovers that it needs a connection to the host.  So it
invokes @samp{telnet @var{host}} or @samp{rsh @var{host} -l
@var{user}} or a similar tool to connect to the remote host.
Communication with this process happens through an
@value{emacsname} buffer, that is, the output from the remote end
goes into a buffer.

@item
The remote host may prompt for a login name (for @command{telnet}).
The login name is given in the file name, so @value{tramp} sends the
login name and a newline.

@item
The remote host may prompt for a password or pass phrase (for
@command{rsh} or for @command{telnet} after sending the login name).
@value{tramp} displays the prompt in the minibuffer, asking you for the
password or pass phrase.

You enter the password or pass phrase.  @value{tramp} sends it to the remote
host, followed by a newline.

@item
@value{tramp} now waits for the shell prompt or for a message that the login
failed.

If @value{tramp} sees neither of them after a certain period of time
(a minute, say), then it issues an error message saying that it
couldn't find the remote shell prompt and shows you what the remote
host has sent.

If @value{tramp} sees a @samp{login failed} message, it tells you so,
aborts the login attempt and allows you to try again.

@item
Suppose that the login was successful and @value{tramp} sees the shell prompt
from the remote host.  Now @value{tramp} invokes @command{/bin/sh} because
Bourne shells and C shells have different command
syntaxes.@footnote{Invoking @command{/bin/sh} will fail if your login
shell doesn't recognize @samp{exec /bin/sh} as a valid command.
Maybe you use the Scheme shell @command{scsh}@dots{}}

After the Bourne shell has come up, @value{tramp} sends a few commands to
ensure a good working environment.  It turns off echoing, it sets the
shell prompt, and a few other things.

@item
Now the remote shell is up and it good working order.  Remember, what
was supposed to happen is that @value{tramp} tries to find out what files exist
on the remote host so that it can do file name completion.

So, @value{tramp} basically issues @command{cd} and @command{ls} commands and
also sometimes @command{echo} with globbing.  Another command that is
often used is @command{test} to find out whether a file is writable or a
directory or the like.  The output of each command is parsed for the
necessary operation.

@item
Suppose you are finished with file name completion, have entered @kbd{C-x
C-f}, a full file name and hit @kbd{@key{RET}}.  Now comes the time to
transfer the file contents from the remote host to the local host so
that you can edit them.

See above for an explanation of how @value{tramp} transfers the file contents.

For inline transfers, @value{tramp} issues a command like @samp{mimencode -b
/path/to/remote/file}, waits until the output has accumulated in the
buffer that's used for communication, then decodes that output to
produce the file contents.

For external transfers, @value{tramp} issues a command like the
following:
@example
rcp user@@host:/path/to/remote/file /tmp/tramp.4711
@end example
It then reads the local temporary file @file{/tmp/tramp.4711} into a
buffer and deletes the temporary file.

@item
You now edit the buffer contents, blithely unaware of what has happened
behind the scenes.  (Unless you have read this section, that is.)  When
you are finished, you type @kbd{C-x C-s} to save the buffer.

@item
Again, @value{tramp} transfers the file contents to the remote host
either inline or external.  This is the reverse of what happens when
reading the file.
@end itemize

I hope this has provided you with a basic overview of what happens
behind the scenes when you open a file with @value{tramp}.


@c For the end user
@node Obtaining Tramp
@chapter Obtaining Tramp.
@cindex obtaining Tramp

@value{tramp} is freely available on the Internet and the latest
release may be downloaded from @uref{ftp://ftp.gnu.org/gnu/tramp/}.
This release includes the full documentation and code for
@value{tramp}, suitable for installation.  But Emacs (22 or later)
includes @value{tramp} already, and there is a @value{tramp} package
for XEmacs, as well.  So maybe it is easier to just use those.  But if
you want the bleeding edge, read on@dots{}

For the especially brave, @value{tramp} is available from Git.  The Git
version is the latest version of the code and may contain incomplete
features or new issues.  Use these versions at your own risk.

Instructions for obtaining the latest development version of @value{tramp}
from Git can be found by going to the Savannah project page at the
following URL and then clicking on the Git link in the navigation bar
at the top.

@noindent
@uref{http://savannah.gnu.org/projects/tramp/}

@noindent
Or follow the example session below:

@example
] @strong{cd ~/@value{emacsdir}}
] @strong{git clone git://git.savannah.gnu.org/tramp.git}
@end example

@noindent
If you reside behind a firewall, you could use

@example
] @strong{git config --global http.proxy http://user:pwd@@proxy.server.com:8080}
] @strong{git clone http://git.savannah.gnu.org/r/tramp.git}
@end example

@noindent
Tramp developers use instead

@example
] @strong{git clone login@@git.sv.gnu.org:/srv/git/tramp.git}
@end example

@noindent
You should now have a directory @file{~/@value{emacsdir}/tramp}
containing the latest version of @value{tramp}.  You can fetch the latest
updates from the repository by issuing the command:

@example
] @strong{cd ~/@value{emacsdir}/tramp}
] @strong{git pull}
@end example

@noindent
Once you've got updated files from the Git repository, you need to run
@command{autoconf} in order to get an up-to-date @file{configure}
script:

@example
] @strong{cd ~/@value{emacsdir}/tramp}
] @strong{autoconf}
@end example


@node History
@chapter History of @value{tramp}
@cindex history
@cindex development history

Development was started end of November 1998.  The package was called
@file{rssh.el}, back then.  It only provided one method to access a
file, using @command{ssh} to log in to a remote host and using
@command{scp} to transfer the file contents.  After a while, the name
was changed to @file{rcp.el}, and now it's @value{tramp}.  Along the way,
many more methods for getting a remote shell and for transferring the
file contents were added.  Support for VC was added.

After that, there were added the multi-hop methods in April 2000 and
the unification of @value{tramp} and Ange-FTP file names in July 2002.
In July 2004, multi-hop methods have been replaced by proxy hosts.
Running commands on remote hosts was introduced in December 2005.
@ifset emacsgw
Support of gateways exists since April 2007.
@end ifset
@ifset emacsgvfs
GVFS integration started in February 2009.
@end ifset
@ifset emacs
Remote commands on Windows hosts are available since September 2011.
@end ifset
Ad-hoc multi-hop methods (with a changed syntax) have been reenabled
in November 2011.  In November 2012, Juergen Hoetzel's
@file{tramp-adb.el} has been added.

In December 2001, @value{tramp} has been added to the XEmacs package
repository.  Being part of the Emacs repository happened in June 2002,
the first release including @value{tramp} was Emacs 22.1.

@value{tramp} is also a Debian GNU/Linux package since February 2001.


@c Installation chapter is necessary only in case of standalone
@c installation.  Text taken from trampinst.texi.
@ifset installchapter
@include trampinst.texi
@end ifset


@node Configuration
@chapter Configuring @value{tramp} for use
@cindex configuration

@cindex default configuration
@value{tramp} is (normally) fully functional when it is initially
installed.  It is initially configured to use the @command{scp}
program to connect to the remote host.  So in the easiest case, you
just type @kbd{C-x C-f} and then enter the file name
@file{@trampfn{, user, host, /path/to.file}}.

On some hosts, there are problems with opening a connection.  These are
related to the behavior of the remote shell.  See @xref{Remote shell
setup}, for details on this.

If you do not wish to use these commands to connect to the remote
host, you should change the default connection and transfer method
that @value{tramp} uses.  There are several different methods that @value{tramp}
can use to connect to remote hosts and transfer files
(@pxref{Connection types}).

If you don't know which method is right for you, see @xref{Default
Method}.

@strong{Note} that the following descriptions reference the setting of
user options or variables, not all of which are autoloaded by
@value{emacsname}.  All examples assume that you have loaded
@value{tramp} first:

@lisp
(require 'tramp)
@end lisp


@menu
* Connection types::            Types of connections made to remote hosts.
* Inline methods::              Inline methods.
* External methods::            External methods.
@ifset emacsgvfs
* GVFS based methods::          GVFS based external methods.
@end ifset
@ifset emacsgw
* Gateway methods::             Gateway methods.
@end ifset
* Default Method::              Selecting a default method.
                                  Here we also try to help those who
                                  don't have the foggiest which method
                                  is right for them.
* Default User::                Selecting a default user.
* Default Host::                Selecting a default host.
* Multi-hops::                  Connecting to a remote host using multiple hops.
* Customizing Methods::         Using Non-Standard Methods.
* Customizing Completion::      Selecting config files for user/host name completion.
* Password handling::           Reusing passwords for several connections.
* Connection caching::          Reusing connection related information.
* Predefined connection information::
                                Setting own connection related information.
* Remote programs::             How @value{tramp} finds and uses programs on the remote host.
* Remote shell setup::          Remote shell setup hints.
* Android shell setup::         Android shell setup hints.
* Auto-save and Backup::        Auto-save and Backup.
* Windows setup hints::         Issues with Cygwin ssh.
@end menu


@node Connection types
@section Types of connections made to remote hosts
@cindex connection types, overview

There are two basic types of transfer methods, each with its own
advantages and limitations.  Both types of connection make use of a
remote shell access program such as @command{rsh}, @command{ssh} or
@command{telnet} to connect to the remote host.

This connection is used to perform many of the operations that @value{tramp}
requires to make the remote file system transparently accessible from
the local host.  It is only when visiting files that the methods
differ.

@cindex inline methods
@cindex external methods
@cindex methods, inline
@cindex methods, external
Loading or saving a remote file requires that the content of the file
be transferred between the two hosts.  The content of the file can
be transferred using one of two methods: the @dfn{inline method} over
the same connection used to log in to the remote host, or the
@dfn{external method} through another connection using a remote copy
program such as @command{rcp}, @command{scp} or @command{rsync}.

The performance of the external methods is generally better than that
of the inline methods, at least for large files.  This is caused by
the need to encode and decode the data when transferring inline.

The one exception to this rule are the @command{scp} based transfer
methods.  While these methods do see better performance when actually
transferring files, the overhead of the cryptographic negotiation at
startup may drown out the improvement in file transfer times.

External methods should be configured such a way that they don't
require a password (with @command{ssh-agent}, or such alike).  Modern
@command{scp} implementations offer options to reuse existing
@command{ssh} connections, which will be enabled by default if
available.  If it isn't possible, you should consider @ref{Password
handling}, otherwise you will be prompted for a password every copy
action.


@node Inline methods
@section Inline methods
@cindex inline methods
@cindex methods, inline

The inline methods in @value{tramp} are quite powerful and can work in
situations where you cannot use an external transfer program to
connect.  There are also strange inline methods which allow you to
transfer files between @emph{user identities} rather than hosts, see
below.

These methods depend on the existence of a suitable encoding and
decoding command on remote host.  Locally, @value{tramp} may be able to
use features of @value{emacsname} to decode and encode the files or
it may require access to external commands to perform that task.

@cindex uuencode
@cindex mimencode
@cindex base-64 encoding
@value{tramp} checks the availability and usability of commands like
@command{mimencode} (part of the @command{metamail} package) or
@command{uuencode} on the remote host.  The first reliable command
will be used.  The search path can be customized, see @ref{Remote
programs}.

If both commands aren't available on the remote host, @value{tramp}
transfers a small piece of Perl code to the remote host, and tries to
apply it for encoding and decoding.

The variable @var{tramp-inline-compress-start-size} controls, whether
a file shall be compressed before encoding.  This could increase
transfer speed for large text files.


@table @asis
@item @option{rsh}
@cindex method rsh
@cindex rsh method

Connect to the remote host with @command{rsh}.  Due to the unsecure
connection it is recommended for very local host topology only.

On operating systems which provide the command @command{remsh} instead
of @command{rsh}, you can use the method @option{remsh}.  This is true
for HP-UX or Cray UNICOS, for example.


@item @option{ssh}
@cindex method ssh
@cindex ssh method

Connect to the remote host with @command{ssh}.  This is identical to
the previous option except that the @command{ssh} package is used,
making the connection more secure.

All the methods based on @command{ssh} have an additional feature: you
can specify a host name which looks like @file{host#42} (the real host
name, then a hash sign, then a port number).  This means to connect to
the given host but to also pass @code{-p 42} as arguments to the
@command{ssh} command.


@item @option{telnet}
@cindex method telnet
@cindex telnet method

Connect to the remote host with @command{telnet}.  This is as unsecure
as the @option{rsh} method.


@item @option{su}
@cindex method su
@cindex su method

This method does not connect to a remote host at all, rather it uses
the @command{su} program to allow you to edit files as another user.
That means, the specified host name in the file name must be either
@samp{localhost} or the host name as returned by the function
@command{(system-name)}.  For an exception of this rule see
@ref{Multi-hops}.


@item @option{sudo}
@cindex method sudo
@cindex sudo method

This is similar to the @option{su} method, but it uses @command{sudo}
rather than @command{su} to become a different user.

Note that @command{sudo} must be configured to allow you to start a
shell as the user.  It would be nice if it was sufficient if
@command{ls} and @command{mimencode} were allowed, but that is not
easy to implement, so I haven't got around to it, yet.


@item @option{sshx}
@cindex method sshx
@cindex sshx method

As you would expect, this is similar to @option{ssh}, only a little
different.  Whereas @option{ssh} opens a normal interactive shell on
the remote host, this option uses @samp{ssh -t -t @var{host} -l
@var{user} /bin/sh} to open a connection.  This is useful for users
where the normal login shell is set up to ask them a number of
questions when logging in.  This procedure avoids these questions, and
just gives @value{tramp} a more-or-less ``standard'' login shell to work
with.

Note that this procedure does not eliminate questions asked by
@command{ssh} itself.  For example, @command{ssh} might ask ``Are you
sure you want to continue connecting?'' if the host key of the remote
host is not known.  @value{tramp} does not know how to deal with such a
question (yet), therefore you will need to make sure that you can log
in without such questions.

This is also useful for Windows users where @command{ssh}, when
invoked from an @value{emacsname} buffer, tells them that it is not
allocating a pseudo tty.  When this happens, the login shell is wont
to not print any shell prompt, which confuses @value{tramp} mightily.

This supports the @samp{-p} argument.


@item @option{krlogin}
@cindex method krlogin
@cindex krlogin method
@cindex Kerberos (with krlogin method)

This method is also similar to @option{ssh}.  It only uses the
@command{krlogin -x} command to log in to the remote host.


@item @option{ksu}
@cindex method ksu
@cindex ksu method
@cindex Kerberos (with ksu method)

This is another method from the Kerberos suite.  It behaves like @option{su}.


@item @option{plink}
@cindex method plink
@cindex plink method

This method is mostly interesting for Windows users using the PuTTY
implementation of SSH@.  It uses @samp{plink -ssh} to log in to the
remote host.

With a recent PuTTY, it is recommended to check the @samp{Share SSH
connections if possible} control for that session.

This method supports the @samp{-P} argument.


@item @option{plinkx}
@cindex method plinkx
@cindex plinkx method

Another method using PuTTY on Windows.  Instead of host names, it
expects PuTTY session names, calling @samp{plink -load @var{session}
-t}.  User names and port numbers must be defined in the session.

With a recent PuTTY, it is recommended to check the @samp{Share SSH
connections if possible} control for that session.

@end table


@node External methods
@section External methods
@cindex methods, external
@cindex external methods

The external methods operate through multiple channels, using the
remote shell connection for many actions while delegating file
transfers to an external transfer utility.

This saves the overhead of encoding and decoding that multiplexing the
transfer through the one connection has with the inline methods.

Since external methods need their own overhead opening a new channel,
all files which are smaller than @var{tramp-copy-size-limit} are still
transferred with the corresponding inline method.  It should provide a
fair trade-off between both approaches.

@table @asis
@item @option{rcp}---@command{rsh} and @command{rcp}
@cindex method rcp
@cindex rcp method
@cindex rcp (with rcp method)
@cindex rsh (with rcp method)

This method uses the @command{rsh} and @command{rcp} commands to connect
to the remote host and transfer files.  This is probably the fastest
connection method available.

The alternative method @option{remcp} uses the @command{remsh} and
@command{rcp} commands.  It should be applied on hosts where
@command{remsh} is used instead of @command{rsh}.


@item @option{scp}---@command{ssh} and @command{scp}
@cindex method scp
@cindex scp method
@cindex scp (with scp method)
@cindex ssh (with scp method)

Using @command{ssh} to connect to the remote host and @command{scp} to
transfer files between the hosts is the best method for securely
connecting to a remote host and accessing files.

The performance of this option is also quite good.  It may be slower than
the inline methods when you often open and close small files however.
The cost of the cryptographic handshake at the start of an @command{scp}
session can begin to absorb the advantage that the lack of encoding and
decoding presents.

All the @command{ssh} based methods support the @samp{-p} feature
where you can specify a port number to connect to in the host name.
For example, the host name @file{host#42} tells @value{tramp} to
specify @samp{-p 42} in the argument list for @command{ssh}, and to
specify @samp{-P 42} in the argument list for @command{scp}.


@item @option{rsync}---@command{ssh} and @command{rsync}
@cindex method rsync
@cindex rsync method
@cindex rsync (with rsync method)
@cindex ssh (with rsync method)

Using the @command{ssh} command to connect securely to the remote
host and the @command{rsync} command to transfer files is almost
identical to the @option{scp} method.

While @command{rsync} performs much better than @command{scp} when
transferring files that exist on both hosts, this advantage is lost if
the file exists only on one side of the connection.  A file can exists
on both the remote and local host, when you copy a file from/to a
remote host.  When you just open a file from the remote host (or write
a file there), a temporary file on the local side is kept as long as
the corresponding buffer, visiting this file, is alive.

This method supports the @samp{-p} argument.


@item @option{scpx}---@command{ssh} and @command{scp}
@cindex method scpx
@cindex scpx method
@cindex scp (with scpx method)
@cindex ssh (with scpx method)

As you would expect, this is similar to @option{scp}, only a little
different.  Whereas @option{scp} opens a normal interactive shell on
the remote host, this option uses @samp{ssh -t -t @var{host} -l
@var{user} /bin/sh} to open a connection.  This is useful for users
where the normal login shell is set up to ask them a number of
questions when logging in.  This procedure avoids these questions, and
just gives @value{tramp} a more-or-less ``standard'' login shell to work
with.

This is also useful for Windows users where @command{ssh}, when
invoked from an @value{emacsname} buffer, tells them that it is not
allocating a pseudo tty.  When this happens, the login shell is wont
to not print any shell prompt, which confuses @value{tramp} mightily.

This method supports the @samp{-p} argument.


@item @option{pscp}---@command{plink} and @command{pscp}
@item @option{psftp}---@command{plink} and @command{psftp}
@cindex method pscp
@cindex pscp method
@cindex pscp (with pscp method)
@cindex plink (with pscp method)
@cindex PuTTY (with pscp method)
@cindex method psftp
@cindex psftp method
@cindex pscp (with psftp method)
@cindex plink (with psftp method)
@cindex PuTTY (with psftp method)

These methods are similar to @option{scp} or @option{sftp}, but they
use the @command{plink} command to connect to the remote host, and
they use @command{pscp} or @command{psftp} for transferring the files.
These programs are part of PuTTY, an SSH implementation for Windows.

With a recent PuTTY, it is recommended to configure the @samp{Share
SSH connections if possible} control for that session.

These methods support the @samp{-P} argument.


@item @option{fcp}---@command{fsh} and @command{fcp}
@cindex method fcp
@cindex fcp method
@cindex fsh (with fcp method)
@cindex fcp (with fcp method)

This method is similar to @option{scp}, but it uses the @command{fsh}
command to connect to the remote host, and it uses @command{fcp} for
transferring the files.  @command{fsh/fcp} are a front-end for
@command{ssh} which allow for reusing the same @command{ssh} session
for submitting several commands.  This avoids the startup overhead of
@command{scp} (which has to establish a secure connection whenever it
is called).  Note, however, that you can also use one of the inline
methods to achieve a similar effect.

This method uses the command @samp{fsh @var{host} -l @var{user}
/bin/sh -i} to establish the connection, it does not work to just say
@command{fsh @var{host} -l @var{user}}.

@cindex method fsh
@cindex fsh method

There is no inline method using @command{fsh} as the multiplexing
provided by the program is not very useful in our context.  @value{tramp}
opens just one connection to the remote host and then keeps it open,
anyway.


@item @option{nc}---@command{telnet} and @command{nc}
@cindex method nc
@cindex nc method
@cindex nc (with nc method)
@cindex telnet (with nc method)

Using @command{telnet} to connect to the remote host and @command{nc}
for file transfer is often the only possibility to access dumb
devices, like routers or NAS hosts.  Those hosts have just a
restricted @command{busybox} as local shell, and there is no program
to encode and decode files for transfer.


@item @option{ftp}
@cindex method ftp
@cindex ftp method

This is not a native @value{tramp} method.  Instead, it forwards all
requests to @value{ftppackagename}.
@ifset xemacs
This works only for unified file names, see @ref{Issues}.
@end ifset


@item @option{smb}---@command{smbclient}
@cindex method smb
@cindex smb method

This is another not native @value{tramp} method.  It uses the
@command{smbclient} command on different Unices in order to connect to
an SMB server.  An SMB server might be a Samba (or CIFS) server on
another UNIX host or, more interesting, a host running MS Windows.  So
far, it is tested against MS Windows NT, MS Windows 2000, MS Windows
XP, MS Windows Vista, and MS Windows 7.

The first directory in the localname must be a share name on the remote
host.  Remember that the @code{$} character, in which default shares
usually end, must be written @code{$$} due to environment variable
substitution in file names.  If no share name is given (i.e., remote
directory @code{/}), all available shares are listed.

Since authorization is done on share level, you will always be
prompted for a password if you access another share on the same host.
This can be suppressed by @ref{Password handling}.

For authorization, MS Windows uses both a user name and a domain name.
Because of this, the @value{tramp} syntax has been extended: you can
specify a user name which looks like @code{user%domain} (the real user
name, then a percent sign, then the domain name).  So, to connect to
the host @code{melancholia} as user @code{daniel} of the domain
@code{BIZARRE}, and edit @file{.emacs} in the home directory (share
@code{daniel$}) I would specify the file name @file{@trampfn{smb,
daniel%BIZARRE, melancholia, /daniel$$/.emacs}}.

Depending on the Windows domain configuration, a Windows user might be
considered as domain user per default.  In order to connect as local
user, the WINS name of that host must be given as domain name.
Usually, it is the host name in capital letters.  In the example
above, the local user @code{daniel} would be specified as
@file{@trampfn{smb, daniel%MELANCHOLIA, melancholia, /daniel$$/.emacs}}.

The domain name as well as the user name are optional.  If no user
name is specified at all, the anonymous user (without password
prompting) is assumed.  This is different from all other @value{tramp}
methods, where in such a case the local user name is taken.

The @option{smb} method supports the @samp{-p} argument.

@strong{Please note:} If @value{emacsname} runs locally under MS
Windows, this method isn't available.  Instead, you can use UNC
file names like @file{//melancholia/daniel$$/.emacs}.  The only
disadvantage is that there's no possibility to specify another user
name.


@item @option{adb}
@cindex method adb
@cindex adb method

This special method uses the Android Debug Bridge for accessing
Android devices.  The Android Debug Bridge must be installed locally.
Some GNU/Linux distributions offer it for installation, otherwise it
can be installed as part of the Android SDK@.  If the @command{adb}
program is not found via the @env{PATH} environment variable, the
variable @var{tramp-adb-program} must point to its absolute path.

@value{tramp} does not connect Android devices to @command{adb},
unless the custom option @option{tramp-adb-connect-if-not-connected}
is non-@code{nil}.  If there is exactly one Android device connected
to @command{adb}, a host name is not needed in the remote file name.
The default @value{tramp} name to be used is @file{@trampfn{adb, , ,}},
therefore.  Otherwise, one could find potential host names with the
command @command{adb devices}.

Usually, the @command{adb} method does not need any user name.  It
runs under the permissions of the @command{adbd} process on the
Android device.  If a user name is specified, @value{tramp} applies an
@command{su} on the device.  This does not work with all Android
devices, especially with unrooted ones.  In that case, an error
message is displayed.

If a device shall be connected via TCP/IP, it is possible to declare
the port number to be used like @file{device#42}.  Without a port
number, the default value as declared in @command{adb} will be used.
Port numbers are not applicable to Android devices connected via USB.

@end table


@ifset emacsgvfs
@node GVFS based methods
@section GVFS based external methods
@cindex methods, gvfs
@cindex gvfs based methods
@cindex dbus

The connection methods described in this section are based on GVFS
@uref{http://en.wikipedia.org/wiki/GVFS}.  Via GVFS, the remote
filesystem is mounted locally through FUSE@.  @value{tramp} uses
this local mounted directory internally.

The communication with GVFS is implemented via D-Bus messages.
Therefore, your @value{emacsname} must have D-Bus integration,
@pxref{Top, , D-Bus, dbus}.

@table @asis
@item @option{dav}
@cindex method dav
@cindex method davs
@cindex dav method
@cindex davs method

This method provides access to WebDAV files and directories.  There
exists also the external method @option{davs}, which uses SSL
encryption for the access.

Both methods support the port number specification as discussed above.


@item @option{obex}
@cindex method obex
@cindex obex method

OBEX is an FTP-like access protocol for simple devices, like cell
phones.  For the time being, @value{tramp} only supports OBEX over Bluetooth.


@item @option{sftp}
@cindex method sftp
@cindex sftp method

As you might expect, this method uses @command{sftp} in order to
access the remote host.  Contrary to the @option{ssh} and @option{scp}
methods, it doesn't open an @command{ssh} session for login.
Therefore, it could be used to access to remote hosts which refuse
@command{ssh} for security reasons.


@item @option{synce}
@cindex method synce
@cindex synce method

The @option{synce} method allows communication with Windows Mobile
devices.  Beside GVFS for mounting remote files and directories via
FUSE, it also needs the SYNCE-GVFS plugin.

@end table

@vindex tramp-gvfs-methods
@defopt tramp-gvfs-methods
This custom option, a list, defines the external methods which shall
be used with GVFS@.  Per default, these are @option{dav},
@option{davs}, @option{obex}, @option{sftp} and @option{synce}.  Other
possible values are @option{ftp} and @option{smb}.
@end defopt
@end ifset


@ifset emacsgw
@node Gateway methods
@section Gateway methods
@cindex methods, gateway
@cindex gateway methods

Gateway methods are not methods to access a remote host directly.
These methods are intended to pass firewalls or proxy servers.
Therefore, they can be used for proxy host declarations
(@pxref{Multi-hops}) only.

A gateway method must always come along with a method which supports
port setting.  This is because @value{tramp} targets the accompanied
method to @file{localhost#random_port}, from where the firewall or
proxy server is accessed.

Gateway methods support user name and password declarations.  These
are used to authenticate towards the corresponding firewall or proxy
server.  They can be passed only if your friendly administrator has
granted your access.

@table @asis
@item @option{tunnel}
@cindex method tunnel
@cindex tunnel method

This method implements an HTTP tunnel via the @command{CONNECT}
command (see RFC 2616, 2817).  Any HTTP 1.1 compliant (proxy) server
shall support this command.

As authentication method, only @option{Basic Authentication} (see RFC
2617) is implemented so far.  If no port number is given in the
declaration, port @option{8080} is used for the proxy server.


@item @option{socks}
@cindex method socks
@cindex socks method

The @command{socks} method provides access to SOCKSv5 servers (see
RFC 1928).  @option{Username/Password Authentication} according to RFC
1929 is supported.

The default port number of the socks server is @option{1080}, if not
specified otherwise.

@end table
@end ifset


@node Default Method
@section Selecting a default method
@cindex default method

@vindex tramp-default-method
When you select an appropriate transfer method for your typical usage
you should set the variable @code{tramp-default-method} to reflect that
choice.  This variable controls which method will be used when a method
is not specified in the @value{tramp} file name.  For example:

@lisp
(setq tramp-default-method "ssh")
@end lisp

@vindex tramp-default-method-alist
You can also specify different methods for certain user/host
combinations, via the variable @code{tramp-default-method-alist}.  For
example, the following two lines specify to use the @option{ssh}
method for all user names matching @samp{john} and the @option{rsync}
method for all host names matching @samp{lily}.  The third line
specifies to use the @option{su} method for the user @samp{root} on
the host @samp{localhost}.

@lisp
(add-to-list 'tramp-default-method-alist '("" "john" "ssh"))
(add-to-list 'tramp-default-method-alist '("lily" "" "rsync"))
(add-to-list 'tramp-default-method-alist
             '("\\`localhost\\'" "\\`root\\'" "su"))
@end lisp

@noindent
See the documentation for the variable
@code{tramp-default-method-alist} for more details.

External methods are normally preferable to inline methods, giving
better performance.

@xref{Inline methods}.
@xref{External methods}.

Another consideration with the selection of transfer methods is the
environment you will use them in and, especially when used over the
Internet, the security implications of your preferred method.

The @option{rsh} and @option{telnet} methods send your password as
plain text as you log in to the remote host, as well as
transferring the files in such a way that the content can easily be
read from other hosts.

If you need to connect to remote systems that are accessible from the
Internet, you should give serious thought to using @option{ssh} based
methods to connect.  These provide a much higher level of security,
making it a non-trivial exercise for someone to obtain your password
or read the content of the files you are editing.


@subsection Which method is the right one for me?
@cindex choosing the right method

Given all of the above, you are probably thinking that this is all fine
and good, but it's not helping you to choose a method!  Right you are.
As a developer, we don't want to boss our users around but give them
maximum freedom instead.  However, the reality is that some users would
like to have some guidance, so here I'll try to give you this guidance
without bossing you around.  You tell me whether it works @dots{}

My suggestion is to use an inline method.  For large files, external
methods might be more efficient, but I guess that most people will
want to edit mostly small files.  And if you access large text files,
compression (driven by @var{tramp-inline-compress-start-size}) shall
still result in good performance.

I guess that these days, most people can access a remote host by
using @command{ssh}.  So I suggest that you use the @option{ssh}
method.  So, type @kbd{C-x C-f @trampfn{ssh, root, otherhost,
/etc/motd} @key{RET}} to edit the @file{/etc/motd} file on the other
host.

If you can't use @option{ssh} to log in to the remote host, then
select a method that uses a program that works.  For instance, Windows
users might like the @option{plink} method which uses the PuTTY
implementation of @command{ssh}.  Or you use Kerberos and thus like
@option{krlogin}.

For the special case of editing files on the local host as another
user, see the @option{su} or @option{sudo} methods.  They offer
shortened syntax for the @samp{root} account, like
@file{@trampfn{su, , , /etc/motd}}.

People who edit large files may want to consider @option{scp} instead
of @option{ssh}, or @option{pscp} instead of @option{plink}.  These
external methods are faster than inline methods for large files.
Note, however, that external methods suffer from some limitations.
Please try first whether you really get a noticeable speed advantage
from using an external method!  Maybe even for large files, inline
methods are fast enough.


@node Default User
@section Selecting a default user
@cindex default user

The user part of a @value{tramp} file name can be omitted.  Usually,
it is replaced by the user name you are logged in.  Often, this is not
what you want.  A typical use of @value{tramp} might be to edit some
files with root permissions on the local host.  This case, you should
set the variable @code{tramp-default-user} to reflect that choice.
For example:

@lisp
(setq tramp-default-user "root")
@end lisp

@code{tramp-default-user} is regarded as obsolete, and will be removed
soon.

@vindex tramp-default-user-alist
You can also specify different users for certain method/host
combinations, via the variable @code{tramp-default-user-alist}.  For
example, if you always have to use the user @samp{john} in the domain
@samp{somewhere.else}, you can specify the following:

@lisp
(add-to-list 'tramp-default-user-alist
             '("ssh" ".*\\.somewhere\\.else\\'" "john"))
@end lisp

@noindent
See the documentation for the variable @code{tramp-default-user-alist}
for more details.

One trap to fall in must be known.  If @value{tramp} finds a default
user, this user will be passed always to the connection command as
parameter (for example @command{ssh here.somewhere.else -l john}.  If
you have specified another user for your command in its configuration
files, @value{tramp} cannot know it, and the remote access will fail.
If you have specified in the given example in @file{~/.ssh/config} the
lines

@example
Host here.somewhere.else
     User lily
@end example

@noindent
than you must discard selecting a default user by @value{tramp}.  This
will be done by setting it to @code{nil} (or @samp{lily}, likewise):

@lisp
(add-to-list 'tramp-default-user-alist
             '("ssh" "\\`here\\.somewhere\\.else\\'" nil))
@end lisp

The last entry in @code{tramp-default-user-alist} could be your
default user you'll apply predominantly.  You shall @emph{append} it
to that list at the end:

@lisp
(add-to-list 'tramp-default-user-alist '(nil nil "jonas") t)
@end lisp


@node Default Host
@section Selecting a default host
@cindex default host

@vindex tramp-default-host
Finally, it is even possible to omit the host name part of a
@value{tramp} file name.  This case, the value of the variable
@code{tramp-default-host} is used.  Per default, it is initialized
with the host name your local @value{emacsname} is running.

If you, for example, use @value{tramp} mainly to contact the host
@samp{target} as user @samp{john}, you can specify:

@lisp
(setq tramp-default-user "john"
      tramp-default-host "target")
@end lisp

Then the simple file name @samp{@trampfn{ssh, , ,}} will connect you
to John's home directory on target.
@ifset emacs
Note, however, that the most simplification @samp{/::} won't work,
because @samp{/:} is the prefix for quoted file names.
@end ifset

@vindex tramp-default-host-alist
Like with methods and users, you can also specify different default
hosts for certain method/user combinations via the variable
@code{tramp-default-host-alist}.  Usually, this isn't necessary,
because @code{tramp-default-host} should be sufficient.  For some
methods, like @option{adb}, that default value must be overwritten,
which is already the initial value of @code{tramp-default-host-alist}.

@noindent
See the documentation for the variable @code{tramp-default-host-alist}
for more details.


@node Multi-hops
@section Connecting to a remote host using multiple hops
@cindex multi-hop
@cindex proxy hosts

Sometimes, the methods described before are not sufficient.
Sometimes, it is not possible to connect to a remote host using a
simple command.  For example, if you are in a secured network, you
might have to log in to a bastion host first before you can connect to
the outside world.  Of course, the target host may also require a
bastion host.

@vindex tramp-default-proxies-alist
@defopt tramp-default-proxies-alist
In order to specify multiple hops, it is possible to define a proxy
host to pass through, via the custom option
@option{tramp-default-proxies-alist}.  This variable keeps a list of
triples (@var{host} @var{user} @var{proxy}).

The first matching item specifies the proxy host to be passed for a
file name located on a remote target matching @var{user}@@@var{host}.
@var{host} and @var{user} are regular expressions or @code{nil}, which
is interpreted as a regular expression which always matches.

@var{proxy} must be a Tramp file name which localname part is ignored.
Method and user name on @var{proxy} are optional, which is interpreted
with the default values.
@ifset emacsgw
The method must be an inline or gateway method (@pxref{Inline
methods}, @pxref{Gateway methods}).
@end ifset
@ifclear emacsgw
The method must be an inline method (@pxref{Inline methods}).
@end ifclear
If @var{proxy} is @code{nil}, no additional hop is required reaching
@var{user}@@@var{host}.

If you, for example, must pass the host @samp{bastion.your.domain} as
user @samp{bird} for any remote host which is not located in your local
domain, you can set

@lisp
(add-to-list 'tramp-default-proxies-alist
             '("\\." nil "@trampfn{ssh, bird, bastion.your.domain,}"))
(add-to-list 'tramp-default-proxies-alist
             '("\\.your\\.domain\\'" nil nil))
@end lisp

Please note the order of the code.  @code{add-to-list} adds elements at the
beginning of a list.  Therefore, most relevant rules must be added last.

Proxy hosts can be cascaded.  If there is another host called
@samp{jump.your.domain}, which is the only one in your local domain who
is allowed connecting @samp{bastion.your.domain}, you can add another
rule:

@lisp
(add-to-list 'tramp-default-proxies-alist
             '("\\`bastion\\.your\\.domain\\'"
               "\\`bird\\'"
               "@trampfn{ssh, , jump.your.domain,}"))
@end lisp

@var{proxy} can contain the patterns @code{%h} or @code{%u}.  These
patterns are replaced by the strings matching @var{host} or
@var{user}, respectively.

If you, for example, wants to work as @samp{root} on hosts in the
domain @samp{your.domain}, but login as @samp{root} is disabled for
non-local access, you might add the following rule:

@lisp
(add-to-list 'tramp-default-proxies-alist
             '("\\.your\\.domain\\'" "\\`root\\'" "@trampfn{ssh, , %h,}"))
@end lisp

Opening @file{@trampfn{sudo, , randomhost.your.domain,}} would connect
first @samp{randomhost.your.domain} via @code{ssh} under your account
name, and perform @code{sudo -u root} on that host afterwards.  It is
important to know that the given method is applied on the host which
has been reached so far.  @code{sudo -u root}, applied on your local
host, wouldn't be useful here.

@var{host}, @var{user} and @var{proxy} can also be Lisp forms.  These
forms are evaluated, and must return a string, or @code{nil}.  The
previous example could be generalized then: For all hosts except my
local one connect via @command{ssh} first, and apply @command{sudo -u
root} afterwards:

@lisp
(add-to-list 'tramp-default-proxies-alist
             '(nil "\\`root\\'" "@trampfn{ssh, , %h,}"))
(add-to-list 'tramp-default-proxies-alist
             '((regexp-quote (system-name)) nil nil))
@end lisp

This is the recommended configuration to work as @samp{root} on remote
Ubuntu hosts.

@ifset emacsgw
Finally, @code{tramp-default-proxies-alist} can be used to pass
firewalls or proxy servers.  Imagine your local network has a host
@samp{proxy.your.domain} which is used on port 3128 as HTTP proxy to
the outer world.  Your friendly administrator has granted you access
under your user name to @samp{host.other.domain} on that proxy
server.@footnote{HTTP tunnels are intended for secure SSL/TLS
communication.  Therefore, many proxy server restrict the tunnels to
related target ports.  You might need to run your ssh server on your
target host @samp{host.other.domain} on such a port, like 443 (https).
See @uref{http://savannah.gnu.org/maintenance/CvsFromBehindFirewall}
for discussion of ethical issues.}  You would need to add the
following rule:

@lisp
(add-to-list 'tramp-default-proxies-alist
             '("\\`host\\.other\\.domain\\'" nil
               "@trampfn{tunnel, , proxy.your.domain#3128,}"))
@end lisp

Gateway methods can be declared as first hop only in a multiple hop
chain.
@end ifset
@end defopt

Hops to be passed tend to be restricted firewalls and alike.
Sometimes they offer limited features only, like running @command{rbash}
(restricted bash).  This must be told to @value{tramp}.

@vindex tramp-restricted-shell-hosts-alist
@defopt tramp-restricted-shell-hosts-alist
This custom option keeps a list of regular expressions, which denote
hosts running a registered shell like @command{rbash}.  Those hosts
can be used as proxies only.

If the bastion host from the example above runs a restricted shell,
you shall apply

@lisp
(add-to-list 'tramp-restricted-shell-hosts-alist
             "\\`bastion\\.your\\.domain\\'")
@end lisp
@end defopt


@node Customizing Methods
@section Using Non-Standard Methods
@cindex customizing methods
@cindex using non-standard methods
@cindex create your own methods

There is a variable @code{tramp-methods} which you can change if the
predefined methods don't seem right.

For the time being, I'll refer you to the Lisp documentation of that
variable, accessible with @kbd{C-h v tramp-methods @key{RET}}.


@node Customizing Completion
@section Selecting config files for user/host name completion
@cindex customizing completion
@cindex selecting config files
@vindex tramp-completion-function-alist

The variable @code{tramp-completion-function-alist} is intended to
customize which files are taken into account for user and host name
completion (@pxref{File name completion}).  For every method, it keeps
a set of configuration files, accompanied by a Lisp function able to
parse that file.  Entries in @code{tramp-completion-function-alist}
have the form (@var{method} @var{pair1} @var{pair2} @dots{}).

Each @var{pair} is composed of (@var{function} @var{file}).
@var{function} is responsible to extract user names and host names
from @var{file} for completion.  There are two functions which access
this variable:

@defun tramp-get-completion-function method
This function returns the list of completion functions for @var{method}.

Example:
@example
(tramp-get-completion-function "rsh")

     @result{} ((tramp-parse-rhosts "/etc/hosts.equiv")
         (tramp-parse-rhosts "~/.rhosts"))
@end example
@end defun

@defun tramp-set-completion-function method function-list
This function sets @var{function-list} as list of completion functions
for @var{method}.

Example:
@example
(tramp-set-completion-function "ssh"
 '((tramp-parse-sconfig "/etc/ssh_config")
   (tramp-parse-sconfig "~/.ssh/config")))

     @result{} ((tramp-parse-sconfig "/etc/ssh_config")
         (tramp-parse-sconfig "~/.ssh/config"))
@end example
@end defun

The following predefined functions parsing configuration files exist:

@table @asis
@item @code{tramp-parse-rhosts}
@findex tramp-parse-rhosts

This function parses files which are syntactical equivalent to
@file{~/.rhosts}.  It returns both host names and user names, if
specified.

@item @code{tramp-parse-shosts}
@findex tramp-parse-shosts

This function parses files which are syntactical equivalent to
@file{~/.ssh/known_hosts}.  Since there are no user names specified
in such files, it can return host names only.

@item @code{tramp-parse-sconfig}
@findex tramp-parse-shosts

This function returns the host nicknames defined by @code{Host} entries
in @file{~/.ssh/config} style files.

@item @code{tramp-parse-shostkeys}
@findex tramp-parse-shostkeys

SSH2 parsing of directories @file{/etc/ssh2/hostkeys/*} and
@file{~/ssh2/hostkeys/*}.  Hosts are coded in file names
@file{hostkey_@var{portnumber}_@var{host-name}.pub}.  User names
are always @code{nil}.

@item @code{tramp-parse-sknownhosts}
@findex tramp-parse-shostkeys

Another SSH2 style parsing of directories like
@file{/etc/ssh2/knownhosts/*} and @file{~/ssh2/knownhosts/*}.  This
case, hosts names are coded in file names
@file{@var{host-name}.@var{algorithm}.pub}.  User names are always @code{nil}.

@item @code{tramp-parse-hosts}
@findex tramp-parse-hosts

A function dedicated to @file{/etc/hosts} style files.  It returns
host names only.

@item @code{tramp-parse-passwd}
@findex tramp-parse-passwd

A function which parses @file{/etc/passwd} like files.  Obviously, it
can return user names only.

@item @code{tramp-parse-netrc}
@findex tramp-parse-netrc

Finally, a function which parses @file{~/.netrc} like files.  This
includes also @file{~/.authinfo}-style files.

@end table

If you want to keep your own data in a file, with your own structure,
you might provide such a function as well.  This function must meet
the following conventions:

@defun my-tramp-parse file
@var{file} must be either a file name on your host, or @code{nil}.
The function must return a list of (@var{user} @var{host}), which are
taken as candidates for user and host name completion.

Example:
@example
(my-tramp-parse "~/.my-tramp-hosts")

     @result{} ((nil "toto") ("daniel" "melancholia"))
@end example
@end defun


@node Password handling
@section Reusing passwords for several connections
@cindex passwords

Sometimes it is necessary to connect to the same remote host several
times.  Reentering passwords again and again would be annoying, when
the chosen method does not support access without password prompt
through own configuration.

The best recommendation is to use the method's own mechanism for
password handling. Consider @command{ssh-agent} for @option{ssh}-like
methods, or @command{pageant} for @option{plink}-like methods.

However, if you cannot apply such native password handling,
@value{tramp} offers alternatives.


@anchor{Using an authentication file}
@subsection Using an authentication file

@vindex auth-sources
The package @file{auth-source.el}, originally developed in No Gnus,
offers the possibility to read passwords from a file, like FTP does it
from @file{~/.netrc}.  The default authentication file is
@file{~/.authinfo.gpg}, this can be changed via the variable
@code{auth-sources}.

@noindent
A typical entry in the authentication file would be

@example
machine melancholia port scp login daniel password geheim
@end example

The port can be any @value{tramp} method (@pxref{Inline methods},
@pxref{External methods}), to match only this method.  When you omit
the port, you match all @value{tramp} methods.

In case of problems, setting @code{auth-source-debug} to @code{t}
gives useful debug messages.


@anchor{Caching passwords}
@subsection Caching passwords

If there is no authentication file, @value{tramp} caches the passwords
entered by you.  They will be reused next time if a connection needs
them for the same user name and host name, independently of the
connection method.

@vindex password-cache-expiry
Passwords are not saved permanently, that means the password caching
is limited to the lifetime of your @value{emacsname} session.  You
can influence the lifetime of password caching by customizing the
variable @code{password-cache-expiry}.  The value is the number of
seconds how long passwords are cached.  Setting it to @code{nil}
disables the expiration.

@vindex password-cache
If you don't like this feature for security reasons, password caching
can be disabled totally by customizing the variable
@code{password-cache} (setting it to @code{nil}).

Implementation Note: password caching is based on the package
@file{password-cache.el}.  For the time being, it is activated only
when this package is seen in the @code{load-path} while loading
@value{tramp}.
@ifset installchapter
If you don't use No Gnus, you can take @file{password.el} from the
@value{tramp} @file{contrib} directory, see @ref{Installation
parameters}.
@end ifset


@node Connection caching
@section Reusing connection related information
@cindex caching

@vindex tramp-persistency-file-name
In order to reduce initial connection time, @value{tramp} stores
connection related information persistently.  The variable
@code{tramp-persistency-file-name} keeps the file name where these
information are written.  Its default value is
@ifset emacs
@file{~/.emacs.d/tramp}.
@end ifset
@ifset xemacs
@file{~/.xemacs/tramp}.
@end ifset
It is recommended to choose a local file name.

@value{tramp} reads this file during startup, and writes it when
exiting @value{emacsname}.  You can simply remove this file if
@value{tramp} shall be urged to recompute these information next
@value{emacsname} startup time.

Using such persistent information can be disabled by setting
@code{tramp-persistency-file-name} to @code{nil}.

Once consequence of reusing connection related information is that
@value{tramp} needs to distinguish hosts.  If you, for example, run a
local @code{sshd} on port 3001, which tunnels @command{ssh} to another
host, you could access both @file{@trampfn{ssh, , localhost,}} and
@file{@trampfn{ssh, , localhost#3001,}}.  @value{tramp} would use the
same host related information (like paths, Perl variants, etc) for
both connections, although the information is valid only for one of
them.

In order to avoid trouble, you must use another host name for one of
the connections, like introducing a @option{Host} section in
@file{~/.ssh/config} (@pxref{Frequently Asked Questions}) or applying
multiple hops (@pxref{Multi-hops}).

When @value{tramp} detects a changed operating system version on a
remote host (via the command @command{uname -sr}), it flushes all
connection related information for this host, and opens the
connection again.


@node Predefined connection information
@section Setting own connection related information

Sometimes, method specific arguments in @code{tramp-methods} do not
fit your needs.  Sometimes, @value{tramp} is not able to detect
correct connection related information.  In such cases, you could tell
@value{tramp} which value it has to take.  Since this could result in
errors, it has to be used with care.

@vindex tramp-connection-properties
Such settings can be performed via the list
@code{tramp-connection-properties}.  An entry in this list has the
form @code{(@var{regexp} @var{property} @var{value})}.  @var{regexp}
matches remote file names for which a property shall be predefined.
It can be @code{nil}.  @var{property} is a string, and @var{value} the
corresponding value.

@var{property} could be any method specific parameter found in
@code{tramp-methods}. The parameter key in @code{tramp-methods} is a
symbol name @code{tramp-<foo>}. In order to overwrite it,
@var{property} must be the string @samp{<foo>}.  If you, for example,
want to change the remote shell to be used on a remote machine, you
could apply

@lisp
(add-to-list 'tramp-connection-properties
             (list (regexp-quote "@trampfn{ssh, user, randomhost.your.domain,}")
                   "remote-shell" "/bin/ksh"))
(add-to-list 'tramp-connection-properties
             (list (regexp-quote "@trampfn{ssh, user, randomhost.your.domain,}")
                   "remote-shell-login" '("-")))
@end lisp

This would overwrite the @code{tramp-remote-shell} and
@code{tramp-remote-shell-login} parameters in @code{tramp-methods}, to
be used on that remote host.

@var{property} could also be any property found in the file
@code{tramp-persistency-file-name}.

A special property is @samp{busybox}.  This must be set, if the remote
host runs a very restricted busybox as shell, which closes the
connection at will.  Since there is no reliable test for this,
@value{tramp} must be indicated this way.  Example:

@lisp
(add-to-list 'tramp-connection-properties
             (list (regexp-quote "@trampfn{ssh, user, randomhost.your.domain,}")
                   "busybox" t))
@end lisp


@node Remote programs
@section How @value{tramp} finds and uses programs on the remote host

@value{tramp} depends on a number of programs on the remote host in order to
function, including @command{ls}, @command{test}, @command{find} and
@command{cat}.

In addition to these required tools, there are various tools that may be
required based on the connection method.  See @ref{Inline methods} and
@ref{External methods} for details on these.

Certain other tools, such as @command{perl} (or @command{perl5}) and
@command{grep} will be used if they can be found.  When they are
available, they are used to improve the performance and accuracy of
remote file access.

@vindex tramp-remote-path
@vindex tramp-default-remote-path
@vindex tramp-own-remote-path
@defopt tramp-remote-path
When @value{tramp} connects to the remote host, it searches for the
programs that it can use.  The custom option
@option{tramp-remote-path} controls the directories searched on the
remote host.

By default, this is set to a reasonable set of defaults for most
hosts.  The symbol @code{tramp-default-remote-path} is a place
holder, it is replaced by the list of directories received via the
command @command{getconf PATH} on your remote host.  For example,
on Debian GNU/Linux this is @file{/bin:/usr/bin}, whereas on Solaris
this is @file{/usr/xpg4/bin:/usr/ccs/bin:/usr/bin:/opt/SUNWspro/bin}.
It is recommended to apply this symbol on top of
@option{tramp-remote-path}.

It is possible, however, that your local (or remote ;) system
administrator has put the tools you want in some obscure local
directory.

In this case, you can still use them with @value{tramp}.  You simply
need to add code to your @file{.emacs} to add the directory to the
remote path.  This will then be searched by @value{tramp} when you
connect and the software found.

To add a directory to the remote search path, you could use code such
as:

@lisp
(add-to-list 'tramp-remote-path "/usr/local/perl/bin")
@end lisp

Another possibility is to reuse the path settings of your remote
account when you log in.  Usually, these settings are overwritten,
because they might not be useful for @value{tramp}.  The place holder
@code{tramp-own-remote-path} preserves these settings.  You can
activate it via

@lisp
(add-to-list 'tramp-remote-path 'tramp-own-remote-path)
@end lisp
@end defopt

@value{tramp} caches several information, like the Perl binary
location.  The changed remote search path wouldn't affect these
settings.  In order to force @value{tramp} to recompute these values,
you must exit @value{emacsname}, remove your persistency file
(@pxref{Connection caching}), and restart @value{emacsname}.


@node Remote shell setup
@section Remote shell setup hints
@cindex remote shell setup
@cindex @file{.profile} file
@cindex @file{.login} file
@cindex shell init files

As explained in the @ref{Overview} section, @value{tramp} connects to the
remote host and talks to the shell it finds there.  Of course, when you
log in, the shell executes its init files.  Suppose your init file
requires you to enter the birth date of your mother; clearly @value{tramp}
does not know this and hence fails to log you in to that host.

There are different possible strategies for pursuing this problem.  One
strategy is to enable @value{tramp} to deal with all possible situations.
This is a losing battle, since it is not possible to deal with
@emph{all} situations.  The other strategy is to require you to set up
the remote host such that it behaves like @value{tramp} expects.  This might
be inconvenient because you have to invest a lot of effort into shell
setup before you can begin to use @value{tramp}.

The package, therefore, pursues a combined approach.  It tries to
figure out some of the more common setups, and only requires you to
avoid really exotic stuff.  For example, it looks through a list of
directories to find some programs on the remote host.  And also, it
knows that it is not obvious how to check whether a file exists, and
therefore it tries different possibilities.  (On some hosts and
shells, the command @command{test -e} does the trick, on some hosts
the shell builtin doesn't work but the program @command{/usr/bin/test
-e} or @command{/bin/test -e} works.  And on still other hosts,
@command{ls -d} is the right way to do this.)

Below you find a discussion of a few things that @value{tramp} does not deal
with, and that you therefore have to set up correctly.

@table @asis
@item @var{shell-prompt-pattern}
@vindex shell-prompt-pattern

After logging in to the remote host, @value{tramp} has to wait for the remote
shell startup to finish before it can send commands to the remote
shell.  The strategy here is to wait for the shell prompt.  In order to
recognize the shell prompt, the variable @code{shell-prompt-pattern} has
to be set correctly to recognize the shell prompt on the remote host.

Note that @value{tramp} requires the match for @code{shell-prompt-pattern}
to be at the end of the buffer.  Many people have something like the
following as the value for the variable: @samp{^[^>$][>$] *}.  Now
suppose your shell prompt is @code{a <b> c $ }.  In this case,
@value{tramp} recognizes the @code{>} character as the end of the prompt,
but it is not at the end of the buffer.

@item @var{tramp-shell-prompt-pattern}
@vindex tramp-shell-prompt-pattern

This regular expression is used by @value{tramp} in the same way as
@code{shell-prompt-pattern}, to match prompts from the remote shell.
This second variable exists because the prompt from the remote shell
might be different from the prompt from a local shell---after all,
the whole point of @value{tramp} is to log in to remote hosts as a
different user.  The default value of
@code{tramp-shell-prompt-pattern} is the same as the default value of
@code{shell-prompt-pattern}, which is reported to work well in many
circumstances.

@item @var{tramp-password-prompt-regexp}
@vindex tramp-password-prompt-regexp
@vindex tramp-wrong-passwd-regexp

During login, @value{tramp} might be forced to enter a password or a
passphrase.  The difference between both is that a password is
requested from the shell on the remote host, while a passphrase is
needed for accessing local authentication information, like your ssh
key.

@var{tramp-password-prompt-regexp} handles the detection of such
requests for English environments.  When you use another localization
of your (local or remote) host, you might need to adapt this.  Example:

@lisp
(setq
  tramp-password-prompt-regexp
    (concat
      "^.*"
      (regexp-opt
        '("passphrase" "Passphrase"
          ;; English
          "password" "Password"
          ;; Deutsch
          "passwort" "Passwort"
          ;; Français
          "mot de passe" "Mot de passe") t)
      ".*:\0? *"))
@end lisp

In parallel, it might also be necessary to adapt
@var{tramp-wrong-passwd-regexp}.

@item @command{tset} and other questions
@cindex Unix command tset
@cindex tset Unix command

Some people invoke the @command{tset} program from their shell startup
scripts which asks the user about the terminal type of the shell.
Maybe some shells ask other questions when they are started.
@value{tramp} does not know how to answer these questions.  There are
two approaches for dealing with this problem.  One approach is to take
care that the shell does not ask any questions when invoked from
@value{tramp}.  You can do this by checking the @env{TERM}
environment variable, it will be set to @code{dumb} when connecting.

@vindex tramp-terminal-type
The variable @code{tramp-terminal-type} can be used to change this value
to @code{dumb}.

@vindex tramp-actions-before-shell
The other approach is to teach @value{tramp} about these questions.  See
the variable @code{tramp-actions-before-shell}.  Example:

@lisp
(defconst my-tramp-prompt-regexp
  (concat (regexp-opt '("Enter the birth date of your mother:") t)
          "\\s-*")
  "Regular expression matching my login prompt question.")

(defun my-tramp-action (proc vec)
  "Enter \"19000101\" in order to give a correct answer."
  (save-window-excursion
    (with-current-buffer (tramp-get-connection-buffer vec)
      (tramp-message vec 6 "\n%s" (buffer-string))
      (tramp-send-string vec "19000101"))))

(add-to-list 'tramp-actions-before-shell
             '(my-tramp-prompt-regexp my-tramp-action))
@end lisp


@item Environment variables named like users in @file{.profile}

If you have a user named frumple and set the variable @env{FRUMPLE} in
your shell environment, then this might cause trouble.  Maybe rename
the variable to @env{FRUMPLE_DIR} or the like.

This weird effect was actually reported by a @value{tramp} user!


@item Non-Bourne commands in @file{.profile}

After logging in to the remote host, @value{tramp} issues the command
@command{exec /bin/sh}.  (Actually, the command is slightly
different.)  When @command{/bin/sh} is executed, it reads some init
files, such as @file{~/.shrc} or @file{~/.profile}.

Now, some people have a login shell which is not @code{/bin/sh} but a
Bourne-ish shell such as bash or ksh.  Some of these people might put
their shell setup into the files @file{~/.shrc} or @file{~/.profile}.
This way, it is possible for non-Bourne constructs to end up in those
files.  Then, @command{exec /bin/sh} might cause the Bourne shell to
barf on those constructs.

As an example, imagine somebody putting @command{export FOO=bar} into
the file @file{~/.profile}.  The standard Bourne shell does not
understand this syntax and will emit a syntax error when it reaches
this line.

Another example is the tilde (@code{~}) character, say when adding
@file{~/bin} to @env{PATH}.  Many Bourne shells will not expand this
character, and since there is usually no directory whose name consists
of the single character tilde, strange things will happen.

What can you do about this?

Well, one possibility is to make sure that everything in
@file{~/.shrc} and @file{~/.profile} on all remote hosts is
Bourne-compatible.  In the above example, instead of @command{export
FOO=bar}, you might use @command{FOO=bar; export FOO} instead.

The other possibility is to put your non-Bourne shell setup into some
other files.  For example, bash reads the file @file{~/.bash_profile}
instead of @file{~/.profile}, if the former exists.  So bash
aficionados just rename their @file{~/.profile} to
@file{~/.bash_profile} on all remote hosts, and Bob's your uncle.

The @value{tramp} developers would like to circumvent this problem, so
if you have an idea about it, please tell us.  However, we are afraid
it is not that simple: before saying @command{exec /bin/sh},
@value{tramp} does not know which kind of shell it might be talking
to.  It could be a Bourne-ish shell like ksh or bash, or it could be a
csh derivative like tcsh, or it could be zsh, or even rc.  If the
shell is Bourne-ish already, then it might be prudent to omit the
@command{exec /bin/sh} step.  But how to find out if the shell is
Bourne-ish?


@item Interactive shell prompt

@value{tramp} redefines the shell prompt in order to parse the shell's
output robustly.  When calling an interactive shell by @kbd{M-x
shell}, this doesn't look nice.

You can redefine the shell prompt by checking the environment variable
@env{INSIDE_EMACS}, which is set by @value{tramp}, in your startup
script @file{~/.emacs_SHELLNAME}. @env{SHELLNAME} might be the string
@code{bash} or similar, in case of doubt you could set it the
environment variable @env{ESHELL} in your @file{.emacs}:

@lisp
(setenv "ESHELL" "bash")
@end lisp

Your file @file{~/.emacs_SHELLNAME} could contain code like

@example
# Reset the prompt for remote Tramp shells.
if [ "$@{INSIDE_EMACS/*tramp*/tramp@}" == "tramp" ] ; then
   PS1="[\u@@\h \w]$ "
fi
@end example

@ifinfo
@ifset emacs
@xref{Interactive Shell, , , @value{emacsdir}}.
@end ifset
@end ifinfo

@item @command{busybox} / @command{nc}
@cindex Unix command nc
@cindex nc Unix command

The @command{nc} command will be used with the @option{nc} method.  On
the remote host, a listener will be installed.  Unfortunately, the
command line syntax for this has been changed with the different
@command{busybox} versions.  @value{tramp} uses the following syntax
(see @code{tramp-methods}):

@example
# nc -l -p 42
@end example

If your remote @command{nc} refuses to accept the @command{-p}
parameter, you could overwrite the syntax with the following form:

@lisp
(add-to-list
 'tramp-connection-properties
 `(,(regexp-quote "192.168.0.1") "remote-copy-args" (("-l") ("%r"))))
@end lisp

@noindent
with @samp{192.168.0.1} being the IP address of your remote host
(@pxref{Predefined connection information}).

@end table


@node Android shell setup
@section Android shell setup hints
@cindex android shell setup

Android devices use a restricted shell.  They can be accessed via the
@option{adb} method.  However, this restricts the access to a USB
connection, and it requires the installation of the Android SDK on the
local host.

When an @command{sshd} process runs on the Android device, like
provided by the @code{SSHDroid} app, any @option{ssh}-based method can
be used.  This requires some special settings.

The default shell @code{/bin/sh} does not exist.  Instead, you shall
use just @code{sh}, which invokes the shell installed on the device.
You can instruct @value{tramp} by this form:

@lisp
(add-to-list 'tramp-connection-properties
             (list (regexp-quote "192.168.0.26") "remote-shell" "sh"))
@end lisp

@noindent
with @samp{192.168.0.26} being the IP address of your Android device
(@pxref{Predefined connection information}).

The user settings for the @env{PATH} environment variable must be
preserved.  It has also been reported, that the commands in
@file{/system/xbin} are better suited than the ones in
@file{/system/bin}.  Add these setting:

@lisp
(add-to-list 'tramp-remote-path 'tramp-own-remote-path)
(add-to-list 'tramp-remote-path "/system/xbin")
@end lisp

@noindent
If the Android device is not @samp{rooted}, you must give the shell a
writable directory for temporary files:

@lisp
(add-to-list 'tramp-remote-process-environment "TMPDIR=$HOME")
@end lisp

@noindent
Now you shall be able to open a remote connection with @kbd{C-x C-f
@trampfn{ssh, , 192.168.0.26#2222, }}, given that @command{sshd}
listens on port @samp{2222}.

It is also recommended to add a corresponding entry to your
@file{~/.ssh/config} for that connection, like

@example
Host android
     HostName 192.168.0.26
     User root
     Port 2222
@end example

@noindent
In this case, you must change the setting for the remote shell to

@lisp
(add-to-list 'tramp-connection-properties
             (list (regexp-quote "android") "remote-shell" "sh"))
@end lisp

@noindent
You would open the connection with @kbd{C-x C-f @trampfn{ssh, ,
android, }} then.


@node Auto-save and Backup
@section Auto-save and Backup configuration
@cindex auto-save
@cindex backup
@ifset emacs
@vindex backup-directory-alist
@end ifset
@ifset xemacs
@vindex bkup-backup-directory-info
@end ifset

Normally, @value{emacsname} writes backup files to the same directory
as the original files, but this behavior can be changed via the
variable
@ifset emacs
@code{backup-directory-alist}.
@end ifset
@ifset xemacs
@code{bkup-backup-directory-info}.
@end ifset
In connection with @value{tramp}, this can have unexpected side
effects.  Suppose that you specify that all backups should go to the
directory @file{~/.emacs.d/backups/}, and then you edit the file
@file{@trampfn{su, root, localhost, /etc/secretfile}}.  The effect is
that the backup file will be owned by you and not by root, thus
possibly enabling others to see it even if they were not intended to
see it.

When
@ifset emacs
@code{backup-directory-alist}
@end ifset
@ifset xemacs
@code{bkup-backup-directory-info}
@end ifset
is @code{nil} (the default), such problems do not occur.

Therefore, it is useful to set special values for @value{tramp}
files.  For example, the following statement effectively ``turns off''
the effect of
@ifset emacs
@code{backup-directory-alist}
@end ifset
@ifset xemacs
@code{bkup-backup-directory-info}
@end ifset
for @value{tramp} files:

@ifset emacs
@lisp
(add-to-list 'backup-directory-alist
             (cons tramp-file-name-regexp nil))
@end lisp
@end ifset
@ifset xemacs
@lisp
(require 'backup-dir)
(add-to-list 'bkup-backup-directory-info
             (list tramp-file-name-regexp ""))
@end lisp
@end ifset

@ifset emacs
It is also possible to disable backups depending on the used method.
The following code disables backups for the @option{su} and
@option{sudo} methods:

@lisp
(setq backup-enable-predicate
      (lambda (name)
        (and (normal-backup-enable-predicate name)
             (not
              (let ((method (file-remote-p name 'method)))
                (when (stringp method)
                  (member method '("su" "sudo"))))))))
@end lisp
@end ifset


Another possibility is to use the @value{tramp} variable
@ifset emacs
@code{tramp-backup-directory-alist}.
@end ifset
@ifset xemacs
@code{tramp-bkup-backup-directory-info}.
@end ifset
This variable has the same meaning like
@ifset emacs
@code{backup-directory-alist}.
@end ifset
@ifset xemacs
@code{bkup-backup-directory-info}.
@end ifset
If a @value{tramp} file is backed up, and DIRECTORY is an absolute
local file name, DIRECTORY is prepended with the @value{tramp} file
name prefix of the file to be backed up.

@noindent
Example:

@ifset emacs
@lisp
(add-to-list 'backup-directory-alist
             (cons "." "~/.emacs.d/backups/"))
(setq tramp-backup-directory-alist backup-directory-alist)
@end lisp
@end ifset
@ifset xemacs
@lisp
(require 'backup-dir)
(add-to-list 'bkup-backup-directory-info
             (list "." "~/.emacs.d/backups/" 'full-path))
(setq tramp-bkup-backup-directory-info bkup-backup-directory-info)
@end lisp
@end ifset

@noindent
The backup file name of @file{@trampfn{su, root, localhost,
/etc/secretfile}} would be
@ifset emacs
@file{@trampfn{su, root, localhost,
~/.emacs.d/backups/!su:root@@localhost:!etc!secretfile~}}
@end ifset
@ifset xemacs
@file{@trampfn{su, root, localhost,
~/.emacs.d/backups/![su!root@@localhost]!etc!secretfile~}}
@end ifset

The same problem can happen with auto-saving files.
@ifset emacs
The variable @code{auto-save-file-name-transforms} keeps information,
on which directory an auto-saved file should go.  By default, it is
initialized for @value{tramp} files to the local temporary directory.

On some versions of @value{emacsname}, namely the version built for
Debian GNU/Linux, the variable @code{auto-save-file-name-transforms}
contains the directory where @value{emacsname} was built.  A
workaround is to manually set the variable to a sane value.

If auto-saved files should go into the same directory as the original
files, @code{auto-save-file-name-transforms} should be set to @code{nil}.

Another possibility is to set the variable
@code{tramp-auto-save-directory} to a proper value.
@end ifset
@ifset xemacs
For this purpose you can set the variable @code{auto-save-directory}
to a proper value.
@end ifset


@node Windows setup hints
@section Issues with Cygwin ssh
@cindex Cygwin, issues

This section needs a lot of work!  Please help.

@cindex method sshx with Cygwin
@cindex sshx method with Cygwin
The recent Cygwin installation of @command{ssh} works only with a
Cygwinized @value{emacsname}.  You can check it by typing @kbd{M-x
eshell}, and starting @kbd{ssh test.host}.  The problem is evident
if you see a message like this:

@example
Pseudo-terminal will not be allocated because stdin is not a terminal.
@end example

Older @command{ssh} versions of Cygwin are told to cooperate with
@value{tramp} selecting @option{sshx} as the connection method.  You
can find information about setting up Cygwin in their FAQ at
@uref{http://cygwin.com/faq/}.

@cindex method scpx with Cygwin
@cindex scpx method with Cygwin
If you wish to use the @option{scpx} connection method, then you might
have the problem that @value{emacsname} calls @command{scp} with a
Windows file name such as @code{c:/foo}.  The Cygwin version of
@command{scp} does not know about Windows file names and interprets
this as a remote file name on the host @code{c}.

One possible workaround is to write a wrapper script for @option{scp}
which converts the Windows file name to a Cygwinized file name.

@cindex Cygwin and ssh-agent
@cindex SSH_AUTH_SOCK and @value{emacsname} on Windows
If you want to use either @option{ssh} based method on Windows, then
you might encounter problems with @command{ssh-agent}.  Using this
program, you can avoid typing the pass-phrase every time you log in.
However, if you start @value{emacsname} from a desktop shortcut, then
the environment variable @env{SSH_AUTH_SOCK} is not set and so
@value{emacsname} and thus @value{tramp} and thus @command{ssh} and
@command{scp} started from @value{tramp} cannot communicate with
@command{ssh-agent}.  It works better to start @value{emacsname} from
the shell.

If anyone knows how to start @command{ssh-agent} under Windows in such a
way that desktop shortcuts can profit, please holler.  I don't really
know anything at all about Windows@dots{}


@node Usage
@chapter Using @value{tramp}
@cindex using @value{tramp}

Once you have installed @value{tramp} it will operate fairly
transparently.  You will be able to access files on any remote host
that you can log in to as though they were local.

Files are specified to @value{tramp} using a formalized syntax specifying the
details of the system to connect to.  This is similar to the syntax used
by the @value{ftppackagename} package.

@cindex type-ahead
Something that might happen which surprises you is that
@value{emacsname} remembers all your keystrokes, so if you see a
password prompt from @value{emacsname}, say, and hit @kbd{@key{RET}}
twice instead of once, then the second keystroke will be processed by
@value{emacsname} after @value{tramp} has done its thing.  Why, this
type-ahead is normal behavior, you say.  Right you are, but be aware
that opening a remote file might take quite a while, maybe half a
minute when a connection needs to be opened.  Maybe after half a
minute you have already forgotten that you hit that key!

@menu
* File name Syntax::            @value{tramp} file name conventions.
* File name completion::        File name completion.
* Ad-hoc multi-hops::           Declaring multiple hops in the file name.
* Remote processes::            Integration with other @value{emacsname} packages.
* Cleanup remote connections::  Cleanup remote connections.
@end menu


@node File name Syntax
@section @value{tramp} file name conventions
@cindex file name syntax
@cindex file name examples

To access the file @var{localname} on the remote host @var{host}
you would specify the file name @file{@trampfn{, , host,
localname}}.  This will connect to @var{host} and transfer the file
using the default method.  @xref{Default Method}.

Some examples of @value{tramp} file names are shown below.

@table @file
@item @value{prefix}melancholia@value{postfix}.emacs
Edit the file @file{.emacs} in your home directory on the host
@code{melancholia}.

@item @value{prefix}melancholia.danann.net@value{postfix}.emacs
This edits the same file, using the fully qualified domain name of
the host.

@item @value{prefix}melancholia@value{postfix}~/.emacs
This also edits the same file; the @file{~} is expanded to your
home directory on the remote host, just like it is locally.

@item @value{prefix}melancholia@value{postfix}~daniel/.emacs
This edits the file @file{.emacs} in the home directory of the user
@code{daniel} on the host @code{melancholia}.  The @file{~<user>}
construct is expanded to the home directory of that user on the remote
host.

@item @value{prefix}melancholia@value{postfix}/etc/squid.conf
This edits the file @file{/etc/squid.conf} on the host
@code{melancholia}.

@end table

@var{host} can also be an IPv4 or IPv6 address, like in
@file{@trampfn{, , 127.0.0.1, .emacs}} or @file{@trampfn{, ,
@value{ipv6prefix}::1@value{ipv6postfix}, .emacs}}.
@ifset emacs
For syntactical reasons, IPv6 addresses must be embedded in square
brackets @file{@value{ipv6prefix}} and @file{@value{ipv6postfix}}.
@end ifset

Unless you specify a different name to use, @value{tramp} will use the
current local user name as the remote user name to log in with.  If you
need to log in as a different user, you can specify the user name as
part of the file name.

To log in to the remote host as a specific user, you use the syntax
@file{@trampfn{, user, host, path/to.file}}.  That means that
connecting to @code{melancholia} as @code{daniel} and editing
@file{.emacs} in your home directory you would specify
@file{@trampfn{, daniel, melancholia, .emacs}}.

It is also possible to specify other file transfer methods
(@pxref{Inline methods}, @pxref{External methods}) as part of the
file name.
@ifset emacs
This is done by putting the method before the user and host name, as
in @file{@value{prefix}@var{method}@value{postfixhop}} (Note the
trailing colon).
@end ifset
@ifset xemacs
This is done by replacing the initial @file{@value{prefix}} with
@file{@value{prefix}<method>@value{postfixhop}}.  (Note the trailing
slash!).
@end ifset
The user, host and file specification remain the same.

So, to connect to the host @code{melancholia} as @code{daniel},
using the @option{ssh} method to transfer files, and edit
@file{.emacs} in my home directory I would specify the file name
@file{@trampfn{ssh, daniel, melancholia, .emacs}}.

@ifset emacs
A remote file name containing a host name only, which is equal to a
method name, is not allowed.  If such a host name is used, it must
always be preceded by an explicit method name, like
@file{@value{prefix}ssh@value{postfixhop}ssh@value{postfix}}.
@end ifset

Finally, for some methods it is possible to specify a different port
number than the default one, given by the method.  This is specified
by adding @file{#<port>} to the host name, like in @file{@trampfn{ssh,
daniel, melancholia#42, .emacs}}.


@node File name completion
@section File name completion
@cindex file name completion

File name completion works with @value{tramp} for completion of method
names, of user names and of host names as well as for completion of
file names on remote hosts.
@ifset emacs
In order to enable this, partial completion must be activated in your
@file{.emacs}.
@ifinfo
@xref{Completion Options, , , @value{emacsdir}}.
@end ifinfo
@end ifset

If you, for example, type @kbd{C-x C-f @value{prefix}t
@key{TAB}}, @value{tramp} might give you as result the choice for

@example
@c @multitable {@trampfn{telnet, , melancholia.danann.net,}} {@trampfn{telnet, , 192.168.0.1,}}
@multitable @columnfractions .5 .5
@ifset emacs
@item @value{prefixhop}telnet@value{postfixhop} @tab tmp/
@item @value{prefixhop}toto@value{postfix} @tab
@end ifset
@ifset xemacs
@item @value{prefixhop}telnet@value{postfixhop} @tab @value{prefixhop}toto@value{postfix}
@end ifset
@end multitable
@end example

@samp{@value{prefixhop}telnet@value{postfixhop}}
is a possible completion for the respective method,
@ifset emacs
@samp{tmp/} stands for the directory @file{/tmp} on your local host,
@end ifset
and @samp{@value{prefixhop}toto@value{postfix}}
might be a host @value{tramp} has detected in your @file{~/.ssh/known_hosts}
file (given you're using default method @option{ssh}).

If you go on to type @kbd{e @key{TAB}}, the minibuffer is completed to
@samp{@value{prefix}telnet@value{postfixhop}}.
Next @kbd{@key{TAB}} brings you all host names @value{tramp} detects in
your @file{/etc/hosts} file, let's say

@example
@multitable @columnfractions .5 .5
@c @multitable {@trampfn{telnet, , melancholia.danann.net,}} {@trampfn{telnet, , 192.168.0.1,}}
@item @trampfn{telnet, , 127.0.0.1,} @tab @trampfn{telnet, , 192.168.0.1,}
@item @trampfn{telnet, , @value{ipv6prefix}::1@value{ipv6postfix},} @tab @trampfn{telnet, , localhost,}
@item @trampfn{telnet, , melancholia.danann.net,} @tab @trampfn{telnet, , melancholia,}
@end multitable
@end example

Now you can choose the desired host, and you can continue to
complete file names on that host.

If the configuration files (@pxref{Customizing Completion}), which
@value{tramp} uses for analysis of completion, offer user names, those user
names will be taken into account as well.

Remote hosts which have been visited in the past and kept
persistently (@pxref{Connection caching}) will be offered too.

Once the remote host identification is completed, it comes to
file name completion on the remote host.  This works pretty much like
for files on the local host, with the exception that minibuffer
killing via a double-slash works only on the file name part, except
that file name part starts with @file{//}.
@ifset emacs
A triple-slash stands for the default behavior.
@end ifset
@ifinfo
@xref{Minibuffer File, , , @value{emacsdir}}.
@end ifinfo

@noindent
Example:

@example
@ifset emacs
@kbd{C-x C-f @trampfn{telnet, , melancholia, /usr/local/bin//etc} @key{TAB}}
     @print{} @trampfn{telnet, , melancholia, /etc}

@kbd{C-x C-f @trampfn{telnet, , melancholia, //etc} @key{TAB}}
     @print{} /etc

@kbd{C-x C-f @trampfn{telnet, , melancholia, /usr/local/bin///etc} @key{TAB}}
     @print{} /etc
@end ifset

@ifset xemacs
@kbd{C-x C-f @trampfn{telnet, , melancholia, /usr/local/bin//}}
     @print{} @trampfn{telnet, , melancholia, /}

@kbd{C-x C-f @trampfn{telnet, , melancholia, //}}
     @print{} /
@end ifset
@end example

A remote directory might have changed its contents out of
@value{emacsname} control, for example by creation or deletion of
files by other processes.  Therefore, during file name completion, the
remote directory contents are reread regularly in order to detect such
changes, which would be invisible otherwise (@pxref{Connection caching}).

@vindex tramp-completion-reread-directory-timeout
@defopt tramp-completion-reread-directory-timeout
This custom option defines the number of seconds since last remote
command before rereading a directory contents.  A value of 0 would
require an immediate reread during file name completion, @code{nil}
means to use always cached values for the directory contents.
@end defopt


@node Ad-hoc multi-hops
@section Declaring multiple hops in the file name
@cindex multi-hop, ad-hoc
@cindex proxy hosts, ad-hoc

Multiple hops are configured with the variable
@code{tramp-default-proxies-alist} (@pxref{Multi-hops}).  However,
sometimes it is desirable to reach a remote host immediately, without
configuration changes.  This can be reached by an ad-hoc specification
of the proxies.

A proxy looks like a remote file name specification without the local
file name part.  It is prepended to the target remote file name,
separated by @samp{|}.  As an example, a remote file on
@samp{you@@remotehost}, passing the proxy @samp{bird@@bastion}, could
be opened by

@example
@c @kbd{C-x C-f @trampfn{ssh@value{postfixhop}bird@@bastion|ssh, you,
@c remotehost, /path}}
@kbd{C-x C-f @value{prefix}ssh@value{postfixhop}bird@@bastion|ssh@value{postfixhop}you@@remotehost@value{postfix}/path}
@end example

Multiple hops can be cascaded, separating all proxies by @samp{|}.
The proxies can also contain the patterns @code{%h} or @code{%u}.

The ad-hoc definition is added on the fly to
@code{tramp-default-proxies-alist}.  Therefore, during the lifetime of
the @value{emacsname} session it is not necessary to enter this ad-hoc
specification, again.  The remote file name @samp{@trampfn{ssh, you,
remotehost, /path}} would be sufficient from now on.

@vindex tramp-save-ad-hoc-proxies
@defopt tramp-save-ad-hoc-proxies
This custom option controls whether ad-hoc definitions are kept
persistently in @option{tramp-default-proxies-alist}.  That means,
those definitions are available also for future @value{emacsname}
sessions.
@end defopt


@node Remote processes
@section Integration with other @value{emacsname} packages
@cindex compile
@cindex recompile

@value{tramp} supports running processes on a remote host.  This
allows to exploit @value{emacsname} packages without modification for
remote file names.  It does not work for the @option{ftp} method.
Association of a pty, as specified in @code{start-file-process}, is
not supported.

@code{process-file} and @code{start-file-process} work on the remote
host when the variable @code{default-directory} is remote:

@lisp
(let ((default-directory "/ssh:remote.host:"))
  (start-file-process "grep" (get-buffer-create "*grep*")
                      "/bin/sh" "-c" "grep -e tramp *"))
@end lisp

@ifset emacsgvfs
If the remote host is mounted via GVFS (see @ref{GVFS based methods}),
the remote filesystem is mounted locally.  Therefore, there are no
remote processes; all processes run still locally on your host with
an adapted @code{default-directory}.  This section does not apply for
such connection methods.
@end ifset

Remote processes are started when a corresponding command is executed
from a buffer belonging to a remote file or directory.  Up to now, the
packages @file{compile.el} (commands like @code{compile} and
@code{grep}) and @file{gud.el} (@code{gdb} or @code{perldb}) have been
integrated.  Integration of further packages is planned, any help for
this is welcome!

When your program is not found in the default search path
@value{tramp} sets on the remote host, you should either use an
absolute path, or extend @code{tramp-remote-path} (see @ref{Remote
programs}):

@lisp
(add-to-list 'tramp-remote-path "~/bin")
(add-to-list 'tramp-remote-path "/appli/pub/bin")
@end lisp

The environment for your program can be adapted by customizing
@code{tramp-remote-process-environment}.  This variable is a list of
strings.  It is structured like @code{process-environment}.  Each
element is a string of the form @samp{ENVVARNAME=VALUE}.  An entry
@samp{ENVVARNAME=} disables the corresponding environment variable,
which might have been set in your init file like @file{~/.profile}.

@noindent
Adding an entry can be performed via @code{add-to-list}:

@lisp
(add-to-list 'tramp-remote-process-environment "JAVA_HOME=/opt/java")
@end lisp

Changing or removing an existing entry is not encouraged.  The default
values are chosen for proper @value{tramp} work.  Nevertheless, if for
example a paranoid system administrator disallows changing the
@env{HISTORY} environment variable, you can customize
@code{tramp-remote-process-environment}, or you can apply the
following code in your @file{.emacs}:

@lisp
(let ((process-environment tramp-remote-process-environment))
  (setenv "HISTORY" nil)
  (setq tramp-remote-process-environment process-environment))
@end lisp

When running @code{process-file} or @code{start-file-process} on a
remote @code{default-directory}, the default settings in
@code{process-environment} are not used as it is the case for local
processes.  However, if you need environment variables other than set
in @code{tramp-remote-process-environment}, you can let-bind them to
@code{process-environment}. Only those variables will be set then:

@lisp
(let ((process-environment (cons "HGPLAIN=1" process-environment)))
  (process-file @dots{}))
@end lisp

This works only for environment variables which are not set already in
@code{process-environment}.

If you use other @value{emacsname} packages which do not run
out-of-the-box on a remote host, please let us know.  We will try to
integrate them as well.  @xref{Bug Reports}.


@subsection Running remote programs that create local X11 windows

If you want to run a remote program, which shall connect the X11
server you are using with your local host, you can set the
@env{DISPLAY} environment variable on the remote host:

@lisp
(add-to-list 'tramp-remote-process-environment
             (format "DISPLAY=%s" (getenv "DISPLAY")))
@end lisp

@noindent
@code{(getenv "DISPLAY")} shall return a string containing a host
name, which can be interpreted on the remote host; otherwise you might
use a fixed host name.  Strings like @code{:0} cannot be used properly
on the remote host.

Another trick might be that you put @code{ForwardX11 yes} or
@code{ForwardX11Trusted yes} to your @file{~/.ssh/config} file for
that host.


@subsection Running @code{shell} on a remote host
@cindex shell

Calling @kbd{M-x shell} in a buffer related to a remote host runs the
local shell as defined in @option{shell-file-name}.  This might be
also a valid file name for a shell to be applied on the remote host,
but it will fail at least when your local and remote hosts belong to
different system types, like @samp{windows-nt} and @samp{gnu/linux}.

You must set the variable @option{explicit-shell-file-name} to the
shell file name on the remote host, in order to start that shell on
the remote host.

@ifset emacs
Starting with Emacs 24 this won't be necessary, if you call
@code{shell} interactively.  You will be asked for the remote shell
file name, if you are on a remote buffer, and if
@option{explicit-shell-file-name} is equal to @code{nil}.
@end ifset


@subsection Running @code{shell-command} on a remote host
@cindex shell-command

@code{shell-command} allows to execute commands in a shell, either
synchronously, either asynchronously.  This works also on remote
hosts.  Example:

@example
@kbd{C-x C-f @trampfn{sudo, , , } @key{RET}}
@kbd{M-! tail -f /var/log/syslog.log & @key{RET}}
@end example

You will see the buffer @file{*Async Shell Command*}, containing the
continuous output of the @command{tail} command.

@ifset emacs
A similar behavior can be reached by @kbd{M-x auto-revert-tail-mode},
if available.
@end ifset


@subsection Running @code{eshell} on a remote host
@cindex eshell

@value{tramp} is integrated into @file{eshell.el}.  That is, you can
open an interactive shell on your remote host, and run commands there.
After you have started @kbd{M-x eshell}, you could perform commands
like this:

@example
@b{~ $} cd @trampfn{sudo, , , /etc} @key{RET}
@b{@trampfn{sudo, root, host, /etc} $} hostname @key{RET}
host
@b{@trampfn{sudo, root, host, /etc} $} id @key{RET}
uid=0(root) gid=0(root) groups=0(root)
@b{@trampfn{sudo, root, host, /etc} $} find-file shadow @key{RET}
#<buffer shadow>
@b{@trampfn{sudo, root, host, /etc} $}
@end example

@ifset emacs
Since @value{emacsname} 23.2, @code{eshell} has also an own
implementation of the @code{su} and @code{sudo} commands.  Both
commands change the default directory of the @file{*eshell*} buffer to
the value related to the user the command has switched to.  This works
even on remote hosts, adding silently a corresponding entry to the
variable @code{tramp-default-proxies-alist} (@pxref{Multi-hops}):

@example
@b{~ $} cd @trampfn{ssh, user, remotehost, /etc} @key{RET}
@b{@trampfn{ssh, user, remotehost, /etc} $} find-file shadow @key{RET}
File is not readable: @trampfn{ssh, user, remotehost, /etc/shadow}
@b{@trampfn{ssh, user, remotehost, /etc} $} sudo find-file shadow @key{RET}
#<buffer shadow>

@b{@trampfn{ssh, user, remotehost, /etc} $} su - @key{RET}
@b{@trampfn{su, root, remotehost, /root} $} id @key{RET}
uid=0(root) gid=0(root) groups=0(root)
@b{@trampfn{su, root, remotehost, /root} $}
@end example
@end ifset


@anchor{Running a debugger on a remote host}
@subsection Running a debugger on a remote host
@cindex gud
@cindex gdb
@cindex perldb

@file{gud.el} offers a unified interface to several symbolic
debuggers
@ifset emacs
@ifinfo
(@ref{Debuggers, , , @value{emacsdir}}).
@end ifinfo
@end ifset
With @value{tramp}, it is possible to debug programs on
remote hosts.  You can call @code{gdb} with a remote file name:

@example
@kbd{M-x gdb @key{RET}}
@b{Run gdb (like this):} gdb --annotate=3 @trampfn{ssh, , host, ~/myprog} @key{RET}
@end example

The file name can also be relative to a remote default directory.
Given you are in a buffer that belongs to the remote directory
@trampfn{ssh, , host, /home/user}, you could call

@example
@kbd{M-x perldb @key{RET}}
@b{Run perldb (like this):} perl -d myprog.pl @key{RET}
@end example

It is not possible to use just the absolute local part of a remote
file name as program to debug, like @kbd{perl -d
/home/user/myprog.pl}, though.

Arguments of the program to be debugged are taken literally.  That
means, file names as arguments must be given as ordinary relative or
absolute file names, without any remote specification.


@subsection Running remote processes on Windows hosts
@cindex winexe
@cindex powershell

With the help of the @command{winexe} it is possible tu run processes
on a remote Windows host.  @value{tramp} has implemented this for
@code{process-file} and @code{start-file-process}.

The variable @code{tramp-smb-winexe-program} must contain the file
name of your local @command{winexe} command.  On the remote host,
Powershell V2.0 must be installed; it is used to run the remote
process.

In order to open a remote shell on the Windows host via @kbd{M-x
shell}, you must set the variables @option{explicit-shell-file-name}
and @option{explicit-*-args}.  If you want, for example, run
@command{cmd}, you must set:

@lisp
(setq explicit-shell-file-name "cmd"
      explicit-cmd-args '("/q"))
@end lisp

@noindent
In case of running @command{powershell} as remote shell, the settings are

@lisp
(setq explicit-shell-file-name "powershell"
      explicit-powershell-args '("-file" "-"))
@end lisp


@node Cleanup remote connections
@section Cleanup remote connections
@cindex cleanup

Sometimes it is useful to cleanup remote connections.  The following
commands support this.

@deffn Command tramp-cleanup-connection vec
This command flushes all connection related objects.  @option{vec} is
the internal representation of a remote connection.  Called
interactively, the command offers all active remote connections in the
minibuffer as remote file name prefix like @file{@trampfn{method,
user, host, }}.  The cleanup includes password cache (@pxref{Password
handling}), file cache, connection cache (@pxref{Connection caching}),
connection buffers.
@end deffn

@deffn Command tramp-cleanup-this-connection
This command flushes all objects of the current buffer's remote
connection.  The same objects are removed as in
@code{tramp-cleanup-connection}.
@end deffn

@deffn Command tramp-cleanup-all-connections
This command flushes objects for all active remote connections.  The
same objects are removed as in @code{tramp-cleanup-connection}.
@end deffn

@deffn Command tramp-cleanup-all-buffers
Like in @code{tramp-cleanup-all-connections}, all remote connections
are cleaned up.  Additionally all buffers, which are related to a
remote connection, are killed.
@end deffn


@node Bug Reports
@chapter Reporting Bugs and Problems
@cindex bug reports

Bugs and problems with @value{tramp} are actively worked on by the
development team.  Feature requests and suggestions are also more than
welcome.

The @value{tramp} mailing list is a great place to get information on
working with @value{tramp}, solving problems and general discussion
and advice on topics relating to the package.  It is moderated so
non-subscribers can post but messages will be delayed, possibly up to
48 hours (or longer in case of holidays), until the moderator approves
your message.

The mailing list is at @email{tramp-devel@@gnu.org}.  Messages sent to
this address go to all the subscribers.  This is @emph{not} the address
to send subscription requests to.

Subscribing to the list is performed via
@uref{http://lists.gnu.org/mailman/listinfo/tramp-devel/,
the @value{tramp} Mail Subscription Page}.

@ifset emacs
@ifset installchapter
Before sending a bug report, you could check whether @value{tramp}
works at all.  Run the test suite on your local host, @ref{Testing}.
@end ifset
@end ifset

@findex tramp-bug
To report a bug in @value{tramp}, you should execute @kbd{M-x
tramp-bug}.  This will automatically generate a buffer with the details
of your system and @value{tramp} version.

When submitting a bug report, please try to describe in excruciating
detail the steps required to reproduce the problem, the setup of the
remote host and any special conditions that exist.  You should also
check that your problem is not described already in @xref{Frequently
Asked Questions}.

If you can identify a minimal test case that reproduces the problem,
include that with your bug report.  This will make it much easier for
the development team to analyze and correct the problem.

Sometimes, there might be also problems due to Tramp caches.  Flush
all caches before running the test, @ref{Cleanup remote connections}.

Before reporting the bug, you should set the verbosity level to 6
(@pxref{Traces and Profiles, Traces}) in the @file{~/.emacs} file and
repeat the bug.  Then, include the contents of the @file{*tramp/foo*}
and @file{*debug tramp/foo*} buffers in your bug report.  A verbosity
level greater than 6 will produce a very huge debug buffer, which is
mostly not necessary for the analysis.

Please be aware that, with a verbosity level of 6 or greater, the
contents of files and directories will be included in the debug
buffer.  Passwords you've typed will never be included there.


@node Frequently Asked Questions
@chapter Frequently Asked Questions
@cindex frequently asked questions
@cindex FAQ

@itemize @bullet
@item
Where can I get the latest @value{tramp}?

@value{tramp} is available under the URL below.

@noindent
@uref{ftp://ftp.gnu.org/gnu/tramp/}

@noindent
There is also a Savannah project page.

@noindent
@uref{http://savannah.gnu.org/projects/tramp/}


@item
Which systems does it work on?

The package has been used successfully on Emacs 22, Emacs 23, Emacs
24, XEmacs 21 (starting with 21.4), and SXEmacs 22.

The package was intended to work on Unix, and it really expects a
Unix-like system on the remote end (except the @option{smb} method),
but some people seemed to have some success getting it to work on MS
Windows XP/Vista/7 @value{emacsname}.


@item
How could I speed up @value{tramp}?

In the backstage, @value{tramp} needs a lot of operations on the
remote host.  The time for transferring data from and to the remote
host as well as the time needed to perform the operations there count.
In order to speed up @value{tramp}, one could either try to avoid some
of the operations, or one could try to improve their performance.

Use an external method, like @option{scp}.

Use caching.  This is already enabled by default.  Information about
the remote host as well as the remote files are cached for reuse.  The
information about remote hosts is kept in the file specified in
@code{tramp-persistency-file-name}.  Keep this file.  If you are
confident that files on remote hosts are not changed out of
@value{emacsname}' control, set @code{remote-file-name-inhibit-cache}
to @code{nil}.  Set also @code{tramp-completion-reread-directory-timeout}
to @code{nil}, @ref{File name completion}.

Disable version control.  If you access remote files which are not
under version control, a lot of check operations can be avoided by
disabling VC@.  This can be achieved by

@lisp
(setq vc-ignore-dir-regexp
      (format "\\(%s\\)\\|\\(%s\\)"
              vc-ignore-dir-regexp
              tramp-file-name-regexp))
@end lisp

Disable excessive traces.  The default trace level of @value{tramp},
defined in the variable @code{tramp-verbose}, is 3.  You should
increase this level only temporarily, hunting bugs.


@item
@value{tramp} does not connect to the remote host

When @value{tramp} does not connect to the remote host, there are three
reasons heading the bug mailing list:

@itemize @minus
@item
Unknown characters in the prompt

@value{tramp} needs to recognize the prompt on the remote host
after execution any command.  This is not possible when the prompt
contains unknown characters like escape sequences for coloring.  This
should be avoided on the remote side.  @xref{Remote shell setup}. for
setting the regular expression detecting the prompt.

You can check your settings after an unsuccessful connection by
switching to the @value{tramp} connection buffer @file{*tramp/foo*},
setting the cursor at the top of the buffer, and applying the expression

@example
@kbd{M-: (re-search-forward (concat tramp-shell-prompt-pattern "$"))}
@end example

If it fails, or the cursor is not moved at the end of the buffer, your
prompt is not recognized correctly.

A special problem is the zsh shell, which uses left-hand side and
right-hand side prompts in parallel.  Therefore, it is necessary to
disable the zsh line editor on the remote host.  You shall add to
@file{~/.zshrc} the following command:

@example
[ $TERM = "dumb" ] && unsetopt zle && PS1='$ '
@end example

Similar fancy prompt settings are known from the fish shell.  Here you
must add in @file{~/.config/fish/config.fish}:

@example
function fish_prompt
  if test $TERM = "dumb"
     echo "\$ "
  else
     @dots{}
  end
end
@end example

Furthermore it has been reported, that @value{tramp} (like sshfs,
incidentally) doesn't work with WinSSHD due to strange prompt settings.

@item
Echoed characters after login

When the remote host opens an echoing shell, there might be control
characters in the welcome message.  @value{tramp} tries to suppress
such echoes via the @command{stty -echo} command, but sometimes this
command is not reached, because the echoed output has confused
@value{tramp} already.  In such situations it might be helpful to use
the @option{sshx} or @option{scpx} methods, which allocate a pseudo tty.
@xref{Inline methods}.

@item
@value{tramp} doesn't transfer strings with more than 500 characters
correctly

On some few systems, the implementation of @code{process-send-string}
seems to be broken for longer strings.  It is reported for HP-UX,
FreeBSD and Tru64 Unix, for example.  This case, you should customize
the variable @code{tramp-chunksize} to 500.  For a description how to
determine whether this is necessary see the documentation of
@code{tramp-chunksize}.

Additionally, it will be useful to set @code{file-precious-flag} to
@code{t} for @value{tramp} files.  Then the file contents will be
written into a temporary file first, which is checked for correct
checksum.
@ifinfo
@pxref{Saving Buffers, , , elisp}
@end ifinfo

@lisp
(add-hook
 'find-file-hook
 (lambda ()
   (when (file-remote-p default-directory)
     (set (make-local-variable 'file-precious-flag) t))))
@end lisp
@end itemize


@item
@value{tramp} does not recognize hung @command{ssh} sessions

When your network connection is down, @command{ssh} sessions might
hang.  @value{tramp} cannot detect it safely, because it still sees a
running @command{ssh} process.  Timeouts cannot be used as well,
because it cannot be predicted how long a remote command will last,
for example when copying very large files.

Therefore, you must configure the @command{ssh} process to die
in such a case.  The following entry in @file{~/.ssh/config} would do
the job:

@example
Host *
     ServerAliveInterval 5
@end example


@item
@value{tramp} does not use my @command{ssh} @code{ControlPath}

Your @code{ControlPath} setting will be overwritten by @command{ssh}
sessions initiated by @value{tramp}.  This is because a master
session, initiated outside @value{emacsname}, could be closed, which
would stall all other @command{ssh} sessions for that host inside
@value{emacsname}.

Consequently, if you connect to a remote host via @value{tramp}, you
might be prompted for a password again, even if you have established
already an @command{ssh} connection to that host.  Further
@value{tramp} connections to that host, for example in order to run a
process on that host, will reuse that initial @command{ssh}
connection.

If your @command{ssh} version supports the @code{ControlPersist}
option, you could customize the variable
@code{tramp-ssh-controlmaster-options} to use your @code{ControlPath},
for example:

@lisp
(setq tramp-ssh-controlmaster-options
      (concat
        "-o ControlPath=/tmp/ssh-ControlPath-%%r@@%%h:%%p "
        "-o ControlMaster=auto -o ControlPersist=yes"))
@end lisp

Note, that "%r", "%h" and "%p" must be encoded as "%%r", "%%h" and
"%%p", respectively.

These settings can be suppressed, if they are configured properly in
your @file{~/.ssh/config}:

@lisp
(setq tramp-use-ssh-controlmaster-options nil)
@end lisp


@item
File name completion does not work with @value{tramp}

When you log in to the remote host, do you see the output of
@command{ls} in color? If so, this may be the cause of your problems.

@command{ls} outputs @acronym{ANSI} escape sequences that your terminal
emulator interprets to set the colors.  These escape sequences will
confuse @value{tramp} however.

In your @file{.bashrc}, @file{.profile} or equivalent on the remote
host you probably have an alias configured that adds the option
@option{--color=yes} or @option{--color=auto}.

You should remove that alias and ensure that a new login @emph{does not}
display the output of @command{ls} in color.  If you still cannot use
file name completion, report a bug to the @value{tramp} developers.


@item
File name completion does not work in large directories

@value{tramp} uses globbing for some operations.  (Globbing means to use the
shell to expand wildcards such as @samp{*.c}.)  This might create long
command lines, especially in directories with many files.  Some shells
choke on long command lines, or don't cope well with the globbing
itself.

If you have a large directory on the remote end, you may wish to execute
a command like @samp{ls -d * ..?* > /dev/null} and see if it hangs.
Note that you must first start the right shell, which might be
@command{/bin/sh}, @command{ksh} or @command{bash}, depending on which
of those supports tilde expansion.


@item
How can I get notified when @value{tramp} file transfers are complete?

The following snippet can be put in your @file{~/.emacs} file.  It
makes @value{emacsname} beep after reading from or writing to the
remote host.

@lisp
(defadvice tramp-handle-write-region
  (after tramp-write-beep-advice activate)
  "Make tramp beep after writing a file."
  (interactive)
  (beep))

(defadvice tramp-handle-do-copy-or-rename-file
  (after tramp-copy-beep-advice activate)
  "Make tramp beep after copying a file."
  (interactive)
  (beep))

(defadvice tramp-handle-insert-file-contents
  (after tramp-insert-beep-advice activate)
  "Make tramp beep after inserting a file."
  (interactive)
  (beep))
@end lisp


@ifset emacs
@item
I'ld like to get a Visual Warning when working in a sudo:ed context

When you are working with @samp{root} privileges, it might be useful
to get an indication in the buffer's modeline.  The following code,
tested with @value{emacsname} 22.1, does the job.  You should put it
into your @file{~/.emacs}:

@lisp
(defun my-mode-line-function ()
  (when (string-match "^/su\\(do\\)?:" default-directory)
    (setq mode-line-format
          (format-mode-line mode-line-format 'font-lock-warning-face))))

(add-hook 'find-file-hook 'my-mode-line-function)
(add-hook 'dired-mode-hook 'my-mode-line-function)
@end lisp
@end ifset


@ifset emacs
@item
I'ld like to see a host indication in the mode line when I'm remote

The following code has been tested with @value{emacsname} 22.1.  You
should put it into your @file{~/.emacs}:

@lisp
(defconst my-mode-line-buffer-identification
  (list
   '(:eval
     (let ((host-name
            (if (file-remote-p default-directory)
                (tramp-file-name-host
                 (tramp-dissect-file-name default-directory))
              (system-name))))
       (if (string-match "^[^0-9][^.]*\\(\\..*\\)" host-name)
           (substring host-name 0 (match-beginning 1))
         host-name)))
   ": %12b"))

(setq-default
 mode-line-buffer-identification
 my-mode-line-buffer-identification)

(add-hook
 'dired-mode-hook
 (lambda ()
   (setq
    mode-line-buffer-identification
    my-mode-line-buffer-identification)))
@end lisp

Since @value{emacsname} 23.1, the mode line contains an indication if
@code{default-directory} for the current buffer is on a remote host.
The corresponding tooltip includes the name of that host.  If you
still want the host name as part of the mode line, you can use the
example above, but the @code{:eval} clause can be simplified:

@lisp
   '(:eval
     (let ((host-name
            (or (file-remote-p default-directory 'host)
                (system-name))))
       (if (string-match "^[^0-9][^.]*\\(\\..*\\)" host-name)
           (substring host-name 0 (match-beginning 1))
         host-name)))
@end lisp
@end ifset


@ifset emacs
@item
My remote host does not understand default directory listing options

@value{emacsname} computes the @command{dired} options depending on
the local host you are working.  If your @command{ls} command on the
remote host does not understand those options, you can change them
like this:

@lisp
(add-hook
 'dired-before-readin-hook
 (lambda ()
   (when (file-remote-p default-directory)
     (setq dired-actual-switches "-al"))))
@end lisp
@end ifset


@item
There's this @file{~/.sh_history} file on the remote host which keeps
growing and growing.  What's that?

Sometimes, @value{tramp} starts @command{ksh} on the remote host for
tilde expansion.  Maybe @command{ksh} saves the history by default.
@value{tramp} tries to turn off saving the history, but maybe you have
to help.  For example, you could put this in your @file{.kshrc}:

@example
if [ -f $HOME/.sh_history ] ; then
   /bin/rm $HOME/.sh_history
fi
if [ "$@{HISTFILE-unset@}" != "unset" ] ; then
   unset HISTFILE
fi
if [ "$@{HISTSIZE-unset@}" != "unset" ] ; then
   unset HISTSIZE
fi
@end example

Furthermore, if you use an @option{ssh}-based method, you could add
the following line to your @file{~/.ssh/environment} file:

@example
HISTFILE=/dev/null
@end example


@item There are longish file names to type.  How to shorten this?

Let's say you need regularly access to @file{@trampfn{ssh, news,
news.my.domain, /opt/news/etc}}, which is boring to type again and
again.  The following approaches can be mixed:

@enumerate

@item Use default values for method and user name:

You can define default methods and user names for hosts,
(@pxref{Default Method}, @pxref{Default User}):

@lisp
(setq tramp-default-method "ssh"
      tramp-default-user "news")
@end lisp

The file name left to type would be
@kbd{C-x C-f @trampfn{, , news.my.domain, /opt/news/etc}}.

Note that there are some useful settings already.  Accessing your
local host as @samp{root} user, is possible just by @kbd{C-x C-f
@trampfn{su, , ,}}.

@item Use configuration possibilities of your method:

Several connection methods (i.e., the programs used) offer powerful
configuration possibilities (@pxref{Customizing Completion}).  In the
given case, this could be @file{~/.ssh/config}:

@example
Host xy
     HostName news.my.domain
     User news
@end example

The file name left to type would be @kbd{C-x C-f @trampfn{ssh, , xy,
/opt/news/etc}}.  Depending on files in your directories, it is even
possible to complete the host name with @kbd{C-x C-f
@value{prefix}ssh@value{postfixhop}x @key{TAB}}.

@item Use environment variables:

File names typed in the minibuffer can be expanded by environment
variables.  You can set them outside @value{emacsname}, or even with
Lisp:

@lisp
(setenv "xy" "@trampfn{ssh, news, news.my.domain, /opt/news/etc/}")
@end lisp

Then you need simply to type @kbd{C-x C-f $xy @key{RET}}, and here you
are.  The disadvantage is that you cannot edit the file name, because
environment variables are not expanded during editing in the
minibuffer.

@item Define own keys:

You can define your own key sequences in @value{emacsname}, which can
be used instead of @kbd{C-x C-f}:

@lisp
(global-set-key
 [(control x) (control y)]
 (lambda ()
   (interactive)
   (find-file
    (read-file-name
     "Find Tramp file: "
     "@trampfn{ssh, news, news.my.domain, /opt/news/etc/}"))))
@end lisp

Simply typing @kbd{C-x C-y} would initialize the minibuffer for
editing with your beloved file name.

See also @uref{http://www.emacswiki.org/cgi-bin/wiki/TrampMode, the
Emacs Wiki} for a more comprehensive example.

@item Define own abbreviation (1):

It is possible to define an own abbreviation list for expanding file
names:

@lisp
(add-to-list
 'directory-abbrev-alist
 '("^/xy" . "@trampfn{ssh, news, news.my.domain, /opt/news/etc/}"))
@end lisp

This shortens the file opening command to @kbd{C-x C-f /xy
@key{RET}}.  The disadvantage is, again, that you cannot edit the file
name, because the expansion happens after entering the file name only.

@item Define own abbreviation (2):

The @code{abbrev-mode} gives more flexibility for editing the
minibuffer:

@lisp
(define-abbrev-table 'my-tramp-abbrev-table
  '(("xy" "@trampfn{ssh, news, news.my.domain, /opt/news/etc/}")))

(add-hook
 'minibuffer-setup-hook
 (lambda ()
   (abbrev-mode 1)
   (setq local-abbrev-table my-tramp-abbrev-table)))

(defadvice minibuffer-complete
  (before my-minibuffer-complete activate)
  (expand-abbrev))

;; If you use partial-completion-mode
(defadvice PC-do-completion
  (before my-PC-do-completion activate)
  (expand-abbrev))
@end lisp

After entering @kbd{C-x C-f xy @key{TAB}}, the minibuffer is
expanded, and you can continue editing.

@item Use bookmarks:

Bookmarks can be used to visit Tramp files or directories.
@ifinfo
@pxref{Bookmarks, , , @value{emacsdir}}
@end ifinfo

When you have opened @file{@trampfn{ssh, news, news.my.domain,
/opt/news/etc/}}, you should save the bookmark via
@ifset emacs
@kbd{@key{menu-bar} @key{edit} @key{bookmarks} @key{set}}.
@end ifset
@ifset xemacs
@kbd{@key{menu-bar} @key{view} @key{bookmarks} @key{set}}.
@end ifset

Later on, you can always navigate to that bookmark via
@ifset emacs
@kbd{@key{menu-bar} @key{edit} @key{bookmarks} @key{jump}}.
@end ifset
@ifset xemacs
@kbd{@key{menu-bar} @key{view} @key{bookmarks} @key{jump}}.
@end ifset

@item Use recent files:

@ifset emacs
@file{recentf}
@end ifset
@ifset xemacs
@file{recent-files}
@end ifset
remembers visited places.
@ifinfo
@ifset emacs
@pxref{File Conveniences, , , @value{emacsdir}}
@end ifset
@ifset xemacs
@pxref{recent-files, , , edit-utils}
@end ifset
@end ifinfo

You could keep remote file names in the recent list without checking
their readability through a remote access:

@lisp
@ifset emacs
(recentf-mode 1)
@end ifset
@ifset xemacs
(recent-files-initialize)
(add-hook
 'find-file-hook
 (lambda ()
   (when (file-remote-p (buffer-file-name))
     (recent-files-make-permanent)))
 'append)
@end ifset
@end lisp

The list of files opened recently is reachable via
@ifset emacs
@kbd{@key{menu-bar} @key{file} @key{Open Recent}}.
@end ifset
@ifset xemacs
@kbd{@key{menu-bar} @key{Recent Files}}.
@end ifset

@ifset emacs
@item Use filecache:

@file{filecache} remembers visited places.  Add the directory into
the cache:

@lisp
(eval-after-load "filecache"
  '(file-cache-add-directory
    "@trampfn{ssh, news, news.my.domain, /opt/news/etc/}"))
@end lisp

Whenever you want to load a file, you can enter @kbd{C-x C-f
C-@key{TAB}} in the minibuffer.  The completion is done for the given
directory.
@end ifset

@ifset emacs
@item Use bbdb:

@file{bbdb} has a built-in feature for @value{ftppackagename} files,
which works also for @value{tramp}.
@ifinfo
@pxref{bbdb-ftp, Storing FTP sites in the BBDB, , bbdb}
@end ifinfo

You need to load @file{bbdb}:

@lisp
(require 'bbdb)
(bbdb-initialize)
@end lisp

Then you can create a BBDB entry via @kbd{M-x bbdb-create-ftp-site}.
Because BBDB is not prepared for @value{tramp} syntax, you must
specify a method together with the user name when needed. Example:

@example
@kbd{M-x bbdb-create-ftp-site @key{RET}}
@b{Ftp Site:} news.my.domain @key{RET}
@b{Ftp Directory:} /opt/news/etc/ @key{RET}
@b{Ftp Username:} ssh@value{postfixhop}news @key{RET}
@b{Company:} @key{RET}
@b{Additional Comments:} @key{RET}
@end example

When you have opened your BBDB buffer, you can access such an entry by
pressing the key @key{F}.
@end ifset

@end enumerate

I would like to thank all @value{tramp} users who have contributed to
the different recipes!


@item I have saved @value{tramp} file names as indicated.  But it
doesn't work in a new @value{emacsname} session!

If you have saved an ad-hoc multi-hop @value{tramp} file name
(@pxref{Ad-hoc multi-hops}) via bookmarks, recent files,
@ifset emacs
filecache, bbdb,
@end ifset
or another package, you must use the full ad-hoc file name including
all hops, like @file{@trampfn{ssh, bird,
bastion|ssh@value{postfixhop}news.my.domain, /opt/news/etc}}.

Alternatively, if you save only the abbreviated multi-hop file name
@file{@trampfn{ssh, news, news.my.domain, /opt/news/etc}}, the custom
option @code{tramp-save-ad-hoc-proxies} must be set to a to a
non-@code{nil} value.


@ifset emacs
@item
How can I use @value{tramp} to connect to a remote @value{emacsname}
session?

You can configure Emacs Client doing this.
@ifinfo
@xref{Emacs Server, , , @value{emacsdir}}.
@end ifinfo

On the remote host, you start the Emacs Server:

@lisp
(require 'server)
(setq server-host (system-name)
      server-use-tcp t)
(server-start)
@end lisp

Make sure that the result of @code{(system-name)} can be resolved on
your local host; otherwise you might use a hard coded IP address.

The resulting file @file{~/.emacs.d/server/server} must be copied to
your local host, at the same location.  You can call then the Emacs
Client from the command line:

@example
emacsclient @trampfn{ssh, user, host, /file/to/edit}
@end example

@code{user} and @code{host} shall be related to your local host.

If you want to use Emacs Client also as editor for other programs, you
could write a script @file{emacsclient.sh}:

@example
#!/bin/sh
emacsclient @trampfn{ssh, $(whoami), $(hostname --fqdn), $1}
@end example

Then you must set the environment variable @env{EDITOR} pointing to
that script:

@example
export EDITOR=/path/to/emacsclient.sh
@end example
@end ifset


@item
There are packages which call @value{tramp} although I haven't entered
a remote file name ever.  I dislike it, how could I disable it?

In general, @value{tramp} functions are used only when
you apply remote file name syntax.  However, some packages enable
@value{tramp} on their own.

@itemize @minus
@item
@file{ido.el}

You could disable @value{tramp} file name completion:

@lisp
(custom-set-variables
 '(ido-enable-tramp-completion nil))
@end lisp

@item
@file{rlogin.el}

You could disable remote directory tracking mode:

@lisp
(rlogin-directory-tracking-mode -1)
@end lisp
@end itemize


@item
How can I disable @value{tramp} at all?

Shame on you, why did you read until now?

@itemize @minus
@ifset emacs
@item
If you just want to have @value{ftppackagename} as default remote
files access package, you should apply the following code:

@lisp
(setq tramp-default-method "ftp")
@end lisp
@end ifset

@item
In order to disable
@ifset emacs
@value{tramp} (and @value{ftppackagename}),
@end ifset
@ifset xemacs
@value{tramp},
@end ifset
you must set @code{tramp-mode} to @code{nil}:

@lisp
(setq tramp-mode nil)
@end lisp

@item
Unloading @value{tramp} can be achieved by applying @kbd{M-x
tramp-unload-tramp}.
@ifset emacs
This resets also the @value{ftppackagename} plugins.
@end ifset
@end itemize
@end itemize


@c For the developer
@node Files directories and localnames
@chapter How file names, directories and localnames are mangled and managed.

@menu
* Localname deconstruction::    Breaking a localname into its components.
@ifset emacs
* External packages::           Integration with external Lisp packages.
@end ifset
@end menu


@node Localname deconstruction
@section Breaking a localname into its components

@value{tramp} file names are somewhat different, obviously, to ordinary file
names.  As such, the lisp functions @code{file-name-directory} and
@code{file-name-nondirectory} are overridden within the @value{tramp}
package.

Their replacements are reasonably simplistic in their approach.  They
dissect the file name, call the original handler on the localname and
then rebuild the @value{tramp} file name with the result.

This allows the platform specific hacks in the original handlers to take
effect while preserving the @value{tramp} file name information.


@ifset emacs
@node External packages
@section Integration with external Lisp packages
@subsection File name completion.

While reading file names in the minibuffer, @value{tramp} must decide
whether it completes possible incomplete file names, or not.  Imagine
there is the following situation: You have typed @kbd{C-x C-f
@value{prefix}ssh@value{postfixhop} @key{TAB}}.  @value{tramp} cannot
know, whether @option{ssh} is a method or a host name.  It checks
therefore the last input character you have typed.  If this is
@key{TAB}, @key{SPACE} or @kbd{?}, @value{tramp} assumes that you are
still in file name completion, and it does not connect to the possible
remote host @option{ssh}.

External packages, which use other characters for completing file names
in the minibuffer, must signal this to @value{tramp}.  For this case,
the variable @code{non-essential} can be bound temporarily to
a non-@code{nil} value.

@lisp
(let ((non-essential t))
  @dots{})
@end lisp


@subsection File attributes cache.

When @value{tramp} runs remote processes, files on the remote host
could change their attributes.  Consequently, @value{tramp} must flush
its complete cache keeping attributes for all files of the remote host
it has seen so far.

This is a performance degradation, because the lost file attributes
must be recomputed when needed again.  In cases where the caller of
@code{process-file} knows that there are no file attribute changes, it
should let-bind the variable @code{process-file-side-effects} to
@code{nil}.  Then @value{tramp} won't flush the file attributes cache.

@lisp
(let (process-file-side-effects)
  @dots{})
@end lisp

For asynchronous processes, @value{tramp} flushes the file attributes
cache via a process sentinel.  If the caller of
@code{start-file-process} knows that there are no file attribute
changes, it should set the process sentinel to the default.  In cases
where the caller defines its own process sentinel, @value{tramp}'s process
sentinel is overwritten.  The caller can still flush the file
attributes cache in its process sentinel with this code:

@lisp
(unless (memq (process-status proc) '(run open))
  (dired-uncache remote-directory))
@end lisp

@code{remote-directory} shall be the root directory, where file
attribute changes can happen during the process lifetime.
@value{tramp} traverses all subdirectories, starting at this
directory.  Often, it is sufficient to use @code{default-directory} of
the process buffer as root directory.
@end ifset


@node Traces and Profiles
@chapter How to Customize Traces

All @value{tramp} messages are raised with a verbosity level.  The
verbosity level can be any number between 0 and 10.  Only messages with
a verbosity level less than or equal to @code{tramp-verbose} are
displayed.

The verbosity levels are

          @w{ 0}  silent (no @value{tramp} messages at all)
@*@indent @w{ 1}  errors
@*@indent @w{ 2}  warnings
@*@indent @w{ 3}  connection to remote hosts (default verbosity)
@*@indent @w{ 4}  activities
@*@indent @w{ 5}  internal
@*@indent @w{ 6}  sent and received strings
@*@indent @w{ 7}  file caching
@*@indent @w{ 8}  connection properties
@*@indent @w{ 9}  test commands
@*@indent @w{10}  traces (huge)

When @code{tramp-verbose} is greater than or equal to 4, the messages
are also written into a @value{tramp} debug buffer.  This debug buffer
is useful for analyzing problems; sending a @value{tramp} bug report
should be done with @code{tramp-verbose} set to a verbosity level of at
least 6 (@pxref{Bug Reports}).

The debug buffer is in
@ifinfo
@ref{Outline Mode, , , @value{emacsdir}}.
@end ifinfo
@ifnotinfo
Outline Mode.
@end ifnotinfo
That means, you can change the level of messages to be viewed.  If you
want, for example, see only messages up to verbosity level 5, you must
enter @kbd{C-u 6 C-c C-q}.
@ifinfo
Other keys for navigating are described in
@ref{Outline Visibility, , , @value{emacsdir}}.
@end ifinfo

@value{tramp} errors are handled internally in order to raise the
verbosity level 1 messages.  When you want to get a Lisp backtrace in
case of an error, you need to set both

@lisp
(setq debug-on-error t
      debug-on-signal t)
@end lisp

Sometimes, it might be even necessary to step through @value{tramp}
function call traces.  Such traces are enabled by the following code:

@lisp
(require 'trace)
(dolist (elt (all-completions "tramp-" obarray 'functionp))
  (trace-function-background (intern elt)))
(untrace-function 'tramp-read-passwd)
(untrace-function 'tramp-gw-basic-authentication)
@end lisp

The function call traces are inserted in the buffer
@file{*trace-output*}.  @code{tramp-read-passwd} and
@code{tramp-gw-basic-authentication} shall be disabled when the
function call traces are added to @value{tramp}, because both
functions return password strings, which should not be distributed.


@node Issues
@chapter Debatable Issues and What Was Decided

@itemize @bullet
@item The uuencode method does not always work.

Due to the design of @value{tramp}, the encoding and decoding programs
need to read from stdin and write to stdout.  On some systems,
@command{uudecode -o -} will read stdin and write the decoded file to
stdout, on other systems @command{uudecode -p} does the same thing.
But some systems have uudecode implementations which cannot do this at
all---it is not possible to call these uudecode implementations with
suitable parameters so that they write to stdout.

Of course, this could be circumvented: the @code{begin foo 644} line
could be rewritten to put in some temporary file name, then
@command{uudecode} could be called, then the temp file could be
printed and deleted.

But I have decided that this is too fragile to reliably work, so on some
systems you'll have to do without the uuencode methods.

@item The @value{tramp} file name syntax differs between Emacs and XEmacs.

The Emacs maintainers wish to use a unified file name syntax for
Ange-FTP and @value{tramp} so that users don't have to learn a new
syntax.  It is sufficient to learn some extensions to the old syntax.

For the XEmacs maintainers, the problems caused from using a unified
file name syntax are greater than the gains.  The XEmacs package system
uses EFS for downloading new packages.  So, obviously, EFS has to be
installed from the start.  If the file names were unified, @value{tramp}
would have to be installed from the start, too.

@ifset xemacs
@strong{Note:} If you'd like to use a similar syntax like
@value{ftppackagename}, you need the following settings in your init
file:

@lisp
(setq tramp-unified-filenames t)
(require 'tramp)
@end lisp

The autoload of the @value{emacsname} @value{tramp} package must be
disabled.  This can be achieved by setting file permissions @code{000}
to the files @file{@dots{}/xemacs-packages/lisp/tramp/auto-autoloads.el*}.

In case of unified file names, all @value{emacsname} download sites are
added to @code{tramp-default-method-alist} with default method
@option{ftp} @xref{Default Method}.  These settings shouldn't be
touched for proper working of the @value{emacsname} package system.

The syntax for unified file names is described in the @value{tramp} manual
for @value{emacsothername}.
@end ifset
@end itemize


@node GNU Free Documentation License
@appendix GNU Free Documentation License
@include doclicense.texi


@node Function Index
@unnumbered Function Index
@printindex fn


@node Variable Index
@unnumbered Variable Index
@printindex vr


@node Concept Index
@unnumbered Concept Index
@printindex cp

@bye

@c TODO
@c
@c * Say something about the .login and .profile files of the remote
@c   shells.
@c * Explain how tramp.el works in principle: open a shell on a remote
@c   host and then send commands to it.
@c * Consistent small or capitalized words especially in menus.
@c * Make a unique declaration of @trampfn.