emacs/man/tramp.texi

\input texinfo   @c -*-texinfo-*-
@c %**start of header
@setfilename ../info/tramp
@settitle TRAMP User Manual
@setchapternewpage odd
@c %**end of header

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

@c In the Tramp CVS, 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 Macros for formatting a filename.
@c trampfn is for a full filename, trampfnmhp means method, host, localname
@c were given, and so on.
@macro trampfn(method, user, host, localname)
@value{prefix}@value{method}@value{user}@@@value{host}@value{postfix}@value{localname}
@end macro

@copying
Copyright @copyright{} 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
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 1.2 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'' in the Emacs manual.

(a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
this GNU Manual, like GNU software.  Copies published by the Free
Software Foundation raise funds for GNU development.''

This document is part of a collection distributed under the GNU Free
Documentation License.  If you want to distribute this document
separately from the collection, you can do so by adding a copy of the
license to the document, as described in section 6 of the license.
@end quotation
@end copying

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

@tex

@titlepage
@title @value{tramp} version @value{trampver} User Manual

@author by Daniel Pittman
@author based on documentation by Kai Gro@ss{}johann

@page
@insertcopying

@end titlepage
@page

@end tex

@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
@ifset jamanual
This manual is also available as a @uref{@value{japanesemanual},
Japanese translation}.
@end ifset

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 CVS 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.
* Concept Index::               An item for each concept.

For the developer:

* Version Control::             The inner workings of remote version control.
* Files directories and localnames::  How file names, directories and localnames are mangled and managed.
* Issues::                      Debatable Issues and What Was Decided.

@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.
* Japanese manual::             Japanese manual.

@end ifset

Configuring @value{tramp} for use

* Connection types::            Types of connections made to remote machines.
* Inline methods::              Inline methods.
* External transfer methods::   External transfer methods.
* Multi-hop Methods::           Connecting to a remote host using multiple hops.
* Default Method::              Selecting a default method.
* Customizing Methods::         Using Non-Standard Methods.
* Customizing Completion::      Selecting config files for user/host name completion.
* Password caching::            Reusing passwords for several connections.
* Remote Programs::             How @value{tramp} finds and uses programs on the remote machine.
* Remote shell setup::          Remote shell setup hints.
* Windows setup hints::         Issues with Cygwin ssh.
* Auto-save and Backup::        Auto-save and Backup.

Using @value{tramp}

* Filename Syntax::             @value{tramp} filename conventions.
* Multi-hop filename syntax::   Multi-hop filename conventions.
* Filename completion::         Filename completion.
* Dired::                       Dired.
* Compilation::                 Compile remote files.

The inner workings of remote version control

* Version Controlled Files::    Determining if a file is under version control.
* Remote Commands::             Executing the version control commands on the remote machine.
* Changed workfiles::           Detecting if the working file has changed.
* Checking out files::          Bringing the workfile out of the repository.
* Miscellaneous Version Control::  Things related to Version Control that don't fit elsewhere.

Things related to Version Control that don't fit elsewhere

* Remote File Ownership::       How VC determines who owns a workfile.
* Back-end Versions::           How VC determines what release your RCS is.

How file names, directories and localnames are mangled and managed

* Localname deconstruction::    Breaking a localname into its components.

@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 machines 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 machine 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 machines, especially if @command{ftp}
access is disabled.

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 machine temporarily.

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

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

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 machine.  These methods are generally
faster for small files.

Within these limitations, @value{tramp} is quite powerful.  It is worth
noting that, as of the time of writing, it is far from a polished
end-user product.  For a while yet you should expect to run into rough
edges and problems with the code now and then.

It is finished enough that the developers use it for day to day work but
the installation and setup can be a little difficult to master, as can
the terminology.

@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 filename 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 filename 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 out-of-band 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 out-of-band.  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 GNU 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 CVS.  The CVS
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 CVS can be found by going to the Savannah project page at the
following URL and then clicking on the CVS 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{export CVS_RSH="ssh"}
] @strong{cvs -z3 -d:ext:anoncvs@@savannah.gnu.org:/cvsroot/tramp co tramp}
@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{export CVS_RSH="ssh"}
] @strong{cvs update -d}
@end example

@noindent
Once you've got updated files from the CVS 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.

The most recent addition of major features were the multi-hop methods
added in April 2000 and the unification of @value{tramp} and Ange-FTP
filenames in July 2002.

@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{ssh} program to connect
to the remote host and to use base64 or uu encoding to transfer the
files through that shell connection.  So in the easiest case, you just
type @kbd{C-x C-f} and then enter the filename
@file{@value{prefix}@var{user}@@@var{machine}@value{postfix}@var{/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 machines and transfer files
(@pxref{Connection types}).

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


@menu
* Connection types::            Types of connections made to remote machines.
* Inline methods::              Inline methods.
* External transfer methods::   External transfer methods.
* Multi-hop Methods::           Connecting to a remote host using multiple hops.
* 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.
* Customizing Methods::         Using Non-Standard Methods.
* Customizing Completion::      Selecting config files for user/host name completion.
* Password caching::            Reusing passwords for several connections.
* Remote Programs::             How @value{tramp} finds and uses programs on the remote machine.
* Remote shell setup::          Remote shell setup hints.
* Windows setup hints::         Issues with Cygwin ssh.
* Auto-save and Backup::        Auto-save and Backup.
@end menu


@node Connection types
@section Types of connections made to remote machines.
@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 machine.

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 machine. It is only when visiting files that the methods
differ.

@cindex inline methods
@cindex external transfer methods
@cindex external methods
@cindex out-of-band methods
@cindex methods, inline
@cindex methods, external transfer
@cindex methods, out-of-band
Loading or saving a remote file requires that the content of the file
be transfered between the two machines. The content of the file can be
transfered over the same connection used to log in to the remote
machine or the file can be transfered through another connection using
a remote copy program such as @command{rcp}, @command{scp} or
@command{rsync}.  The former are called @dfn{inline methods}, the
latter are called @dfn{out-of-band methods} or @dfn{external transfer
methods} (@dfn{external methods} for short).

The performance of the external transfer 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 transfer methods should be configured such a way that they
don't require a password (with @command{ssh-agent}, or such alike).
If it isn't possible, you should consider @ref{Password caching},
otherwise you will be prompted for a password every copy action.

@cindex multi-hop methods
@cindex methods, multi-hop
A variant of the inline methods are the @dfn{multi-hop methods}.
These methods allow you to connect a remote host using a number `hops',
each of which connects to a different host.  This is useful if you are
in a secured network where you need to go through a bastion host to
connect to the outside world.


@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.
Inline methods are the only methods that work when connecting to the
remote machine via telnet.  (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 machine.  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.


@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.

There are also two variants, @option{ssh1} and @option{ssh2}, that
call @samp{ssh -1} and @samp{ssh -2}, respectively.  This way, you can
explicitly select whether you want to use the SSH protocol version 1
or 2 to connect to the remote host.  (You can also specify in
@file{~/.ssh/config}, the SSH configuration file, which protocol
should be used, and use the regular @option{ssh} method.)

Two other variants, @option{ssh1_old} and @option{ssh2_old}, use the
@command{ssh1} and @command{ssh2} commands explicitly.  If you don't
know what these are, you do not need these options.

All the methods based on @command{ssh} have an additional kludgy
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.


@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.
For reasons unknown, some Windows ports for @command{ssh} require the
doubled @samp{-t} option.

This supports the @samp{-p} kludge.


@item @option{krlogin}
@cindex method krlogin
@cindex km krlogin
@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{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.

Additionally, the method @option{plink1} is provided, which calls
@samp{plink -1 -ssh} in order to use SSH protocol version 1
explicitely.

CCC: Do we have to connect to the remote host once from the command
line to accept the SSH key?  Maybe this can be made automatic?

CCC: Does @command{plink} support the @samp{-p} option?  @value{tramp} will
support that, anyway.

@end table



@node External transfer methods
@section External transfer methods
@cindex methods, external transfer
@cindex methods, out-of-band
@cindex external transfer methods
@cindex out-of-band methods

The external transfer 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.

If you want to use an external transfer method you should be able to
execute the transfer utility to copy files to and from the remote
machine without any interaction.

@cindex ssh-agent
This means that you will need to use @command{ssh-agent} if you use the
@command{scp} program for transfers, or maybe your version of
@command{scp} accepts a password on the command line.@footnote{PuTTY's
@command{pscp} allows you to specify the password on the command line.}
If you use @command{rsync} via @command{ssh} then the same rule must
apply to that connection.

If you cannot get an external method to run without asking for a
password you should consider @ref{Password caching}.


@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 machine 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 machines 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 machines is the best method for securely
connecting to a remote machine 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.

There are also two variants, @option{scp1} and @option{scp2}, that
call @samp{ssh -1} and @samp{ssh -2}, respectively.  This way, you can
explicitly select whether you want to use the SSH protocol version 1
or 2 to connect to the remote host.  (You can also specify in
@file{~/.ssh/config}, the SSH configuration file, which protocol
should be used, and use the regular @option{scp} method.)

Two other variants, @option{scp1_old} and @option{scp2_old}, use the
@command{ssh1} and @command{ssh2} commands explicitly.  If you don't
know what these are, you do not need these options.

All the @command{ssh} based methods support the kludgy @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}.


@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
machine 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.

The @command{rsync} based method may be considerably faster than the
@command{rcp} based methods when writing to the remote system. Reading
files to the local machine is no faster than with a direct copy.

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


@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} hack.


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

This method is similar to @option{scp}, but it uses the
@command{plink} command to connect to the remote host, and it uses
@command{pscp} for transferring the files.  These programs are part
of PuTTY, an SSH implementation for Windows.

CCC: Does @command{plink} support the @samp{-p} hack?


@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{ftp}
@cindex method ftp
@cindex ftp method

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


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

This is another not natural @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 towards MS Windows NT, MS Windows 2000, and MS
Windows XP.

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 be prompted
always for a password if you access another share on the same host.
This can be suppressed by @ref{Password caching}.

MS Windows uses for authorization 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 machine @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 filename
@file{@value{prefix}smb@value{postfixsinglehop}daniel%BIZARRE@@melancholia@value{postfix}/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} hack.

@strong{Please note:} If @value{emacsname} runs locally under MS
Windows, this method isn't available.  Instead of, 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.

@end table

@node Multi-hop Methods
@section Connecting to a remote host using multiple hops
@cindex multi-hop methods
@cindex methods, multi-hop

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.  The format
of multi-hop filenames is slightly different than the format of normal
@value{tramp} methods.

@cindex method multi
@cindex multi method
A multi-hop file name specifies a method, a number of hops, and a
localname (path name on the remote system).  The method name is always
@option{multi}.

Each hop consists of a @dfn{hop method} specification, a user name and
a host name.  The hop method can be an inline method only.  The
following hop methods are (currently) available:

@table @option
@item telnet
@cindex hop method telnet
@cindex telnet hop method

Uses the well-known @command{telnet} program to connect to the host.
Whereas user name and host name are supplied in the file name, the
user is queried for the password.

@item rsh
@cindex hop method rsh
@cindex rsh hop method

This uses @command{rsh} to connect to the host.  You do not need to
enter a password unless @command{rsh} explicitly asks for it.

The variant @option{remsh} uses the @command{remsh} command.  It
should be applied on machines where @command{remsh} is used instead of
@command{rsh}.

@item ssh
@cindex hop method ssh
@cindex ssh hop method

This uses @command{ssh} to connect to the host.  You might have to enter
a password or a pass phrase.

@item su
@cindex hop method su
@cindex su hop method

This method does not actually contact a different host, but it allows
you to become a different user on the host you're currently on.  This
might be useful if you want to edit files as root, but the remote host
does not allow remote root logins.  In this case you can use
@option{telnet}, @option{rsh} or @option{ssh} to connect to the
remote host as a non-root user, then use an @option{su} hop to become
root.  But @option{su} need not be the last hop in a sequence, you could
also use it somewhere in the middle, if the need arises.

Even though you @emph{must} specify both user and host with an
@option{su} hop, the host name is ignored and only the user name is
used.

@item sudo
@cindex hop method sudo
@cindex sudo hop method

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

@end table

Some people might wish to use port forwarding with @command{ssh} or
maybe they have to use a nonstandard port.  This can be accomplished
by putting a stanza in @file{~/.ssh/config} for the account which
specifies a different port number for a certain host name.  But it can
also be accomplished within @value{tramp}, by adding a multi-hop method.
For example:

@lisp
(add-to-list
 'tramp-multi-connection-function-alist
 '("sshf" tramp-multi-connect-rlogin "ssh %h -l %u -p 4400%n"))
@end lisp

Now you can use an @option{sshf} hop which connects to port 4400 instead of
the standard port.


@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 "scp")
@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 machine @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 transfer methods are normally preferable to inline transfer
methods, giving better performance.

@xref{Inline methods}.
@xref{External transfer methods}.
@xref{Multi-hop 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 machine, as well as
transferring the files in such a way that the content can easily be
read from other machines.

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, out-of-band
methods might be more efficient, but I guess that most people will want
to edit mostly small files.

I guess that these days, most people can access a remote machine by
using @command{ssh}.  So I suggest that you use the @option{ssh}
method.  So, type @kbd{C-x C-f
@value{prefix}ssh@value{postfixsinglehop}root@@otherhost@value{postfix}/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{@value{prefix}su@value{postfixsinglehop}@value{postfix}/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
out-of-band methods are faster than inline methods for large files.
Note, however, that out-of-band methods suffer from some limitations.
Please try first whether you really get a noticeable speed advantage
from using an out-of-band method!  Maybe even for large files, inline
methods are fast enough.


@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{Filename 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} ...).

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.
@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 caching
@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 choosen method does not support access without password prompt
throught own configuration.

By default, @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, independant 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.

@findex tramp-clear-passwd
A password is removed from the cache if a connection isn't established
successfully.  You can remove a password from the cache also by
executing @kbd{M-x tramp-clear-passwd} in a buffer containing a
related remote file or directory.

@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
password.el in No Gnus.  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 password.el from the @value{tramp}
@file{contrib} directory, see @ref{Installation parameters}.
@end ifset
It will be activated mandatory once No Gnus has found its way into
@value{emacsname}.


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

@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 transfer 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
When @value{tramp} connects to the remote machine, it searches for the
programs that it can use. The variable @var{tramp-remote-path} controls
the directories searched on the remote machine.

By default, this is set to a reasonable set of defaults for most
machines. 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
@i{;; We load @value{tramp} to define the variable.}
(require 'tramp)
@i{;; We have @command{perl} in "/usr/local/perl/bin"}
(add-to-list 'tramp-remote-path "/usr/local/perl/bin")
@end lisp


@node Remote shell setup
@comment  node-name,  next,  previous,  up
@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: @code{"^[^>$][>$] *"}.  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 @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 @code{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}.

The other approach is to teach @value{tramp} about these questions.  See
the variables @code{tramp-actions-before-shell} and
@code{tramp-multi-actions} (for multi-hop connections).


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

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

@end table


@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{@value{prefix}su@value{postfixsinglehop}root@@localhost@value{postfix}/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 usefull 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

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{@value{prefix}su@value{postfixsinglehop}root@@localhost@value{postfix}/etc/secretfile}
would be
@ifset emacs
@file{@value{prefix}su@value{postfixsinglehop}root@@localhost@value{postfix}~/.emacs.d/backups/!su:root@@localhost:!etc!secretfile~}
@end ifset
@ifset xemacs
@file{@value{prefix}su@value{postfixsinglehop}root@@localhost@value{postfix}~/.emacs.d/backups/![su!root@@localhost]!etc!secretfile~}
@end ifset

The same problem can happen with auto-saving files.
@ifset emacs
Since @value{emacsname} 21, 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.machine}.  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 filename such as @code{c:/foo}.  The Cygwin version of
@command{scp} does not know about Windows filenames and interprets this
as a remote filename on the host @code{c}.

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

@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 @code{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 machine 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
* Filename Syntax::             @value{tramp} filename conventions.
* Multi-hop filename syntax::   Multi-hop filename conventions.
* Filename completion::         Filename completion.
* Dired::                       Dired.
* Compilation::                 Compile remote files.
@end menu


@node Filename Syntax
@section @value{tramp} filename conventions
@cindex filename syntax
@cindex filename examples

To access the file @var{localname} on the remote machine @var{machine} you
would specify the filename
@file{@value{prefix}@var{machine}@value{postfix}@var{localname}}.
This will connect to @var{machine} and transfer the file using the
default method.  @xref{Default Method}.

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

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

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

@item @value{prefix}melancholia@value{postfix}~/.emacs
This also edits the same file --- the @file{~} is expanded to your
home directory on the remote machine, 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 machine @code{melancholia}. The @file{~<user>}
construct is expanded to the home directory of that user on the remote
machine.

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

@end table

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 filename.

To log in to the remote machine as a specific user, you use the syntax
@file{@value{prefix}@var{user}@@@var{machine}@value{postfix}/@var{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{@value{prefix}daniel@@melancholia@value{postfix}.emacs}.

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

So, to connect to the machine @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 filename
@file{@value{prefix}ssh@value{postfixsinglehop}daniel@@melancholia@value{postfix}.emacs}.


@node Multi-hop filename syntax
@section Multi-hop filename conventions
@cindex filename syntax for multi-hop files
@cindex multi-hop filename syntax

The syntax of multi-hop file names is necessarily slightly different
than the syntax of other @value{tramp} file names.  Here's an example
multi-hop file name:

@example
@value{prefix}multi@value{postfixsinglehop}rsh@value{postfixmultihop}out@@gate@value{postfixsinglehop}telnet@value{postfixmultihop}kai@@real.host@value{postfix}/path/to.file
@end example

This is quite a mouthful.  So let's go through it step by step.  The
file name consists of three parts.
@ifset emacs
The parts are separated by colons
@end ifset
@ifset xemacs
The parts are separated by slashes and square brackets.
@end ifset
The first part is @file{@value{prefix}multi}, the method
specification.  The second part is
@file{rsh@value{postfixmultihop}out@@gate@value{postfixsinglehop}telnet@value{postfixmultihop}kai@@real.host}
and specifies the hops.  The final part is @file{/path/to.file} and
specifies the file name on the remote host.

The first part and the final part should be clear.  See @ref{Multi-hop
Methods}, for a list of alternatives for the method specification.

The second part can be subdivided again into components, so-called
hops.  In the above file name, there are two hops,
@file{rsh@value{postfixmultihop}out@@gate} and
@file{telnet@value{postfixmultihop}kai@@real.host}.

Each hop can @emph{again} be subdivided into (three) components, the
@dfn{hop method}, the @dfn{user name} and the @dfn{host name}.  The
meaning of the second and third component should be clear, and the hop
method says what program to use to perform that hop.

The first hop, @file{rsh@value{postfixmultihop}out@@gate},
says to use @command{rsh} to log in as user @code{out} to the host
@code{gate}.  Starting at that host, the second hop,
@file{telnet@value{postfixmultihop}kai@@real.host}, says to
use @command{telnet} to log in as user @code{kai} to host
@code{real.host}.

@xref{Multi-hop Methods}, for a list of possible hop method values.
The variable @code{tramp-multi-connection-function-alist} contains the
list of possible hop methods and information on how to execute them,
should you want to add your own.


@node Filename completion
@section Filename completion
@cindex filename completion

Filename completion works with @value{tramp} for both completing methods,
user names and machine names (except multi hop methods) as well as for
files on remote machines.

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
@ifset emacs
@value{prefixsinglehop}telnet@value{postfixsinglehop}				   tmp/
@value{prefixsinglehop}toto@value{postfix}
@end ifset
@ifset xemacs
@value{prefixsinglehop}telnet@value{postfixsinglehop}				   @value{prefixsinglehop}toto@value{postfix}
@end ifset
@end example

@samp{@value{prefixsinglehop}telnet@value{postfixsinglehop}}
is a possible completion for the respective method,
@ifset emacs
@samp{tmp/} stands for the directory @file{/tmp} on your local
machine,
@end ifset
and @samp{@value{prefixsinglehop}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{postfixsinglehop}}.
Next @kbd{@key{TAB}} brings you all machine names @value{tramp} detects in
your @file{/etc/hosts} file, let's say

@example
@value{prefixsinglehop}telnet@value{postfixsinglehop}127.0.0.1@value{postfix}		   @value{prefixsinglehop}telnet@value{postfixsinglehop}192.168.0.1@value{postfix}
@value{prefixsinglehop}telnet@value{postfixsinglehop}localhost@value{postfix}		   @value{prefixsinglehop}telnet@value{postfixsinglehop}melancholia.danann.net@value{postfix}
@value{prefixsinglehop}telnet@value{postfixsinglehop}melancholia@value{postfix}
@end example

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

As filename completion needs to fetch the listing of files from the
remote machine, this feature is sometimes fairly slow.  As @value{tramp}
does not yet cache the results of directory listing, there is no gain
in performance the second time you complete filenames.

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.


@node Dired
@section Dired
@cindex dired

@value{tramp} works transparently with dired, enabling you to use this powerful
file management tool to manage files on any machine you have access to
over the Internet.

If you need to browse a directory tree, Dired is a better choice, at
present, than filename completion.  Dired has its own cache mechanism
and will only fetch the directory listing once.


@node Compilation
@section Compile remote files
@cindex compile
@cindex recompile

@value{tramp} provides commands for compilation of files on remote
machines.  In order to get them loaded, you need to require
@file{tramp-util.el}:

@lisp
(require 'tramp-util)
@end lisp

Afterwards, you can use the commands @code{tramp-compile} and
@code{tramp-recompile} instead of @code{compile} and @code{recompile},
respectively; @inforef{Compilation, ,@value{emacsdir}}.  This does not
work for the @option{ftp} and @option{smb} methods.

The corresponding key bindings and menu entries calling these commands
are redefined automatically for buffers associated with remote files.

After finishing the compilation, you can use the usual commands like
@code{previous-error}, @code{next-error} and @code{first-error} for
navigation in the @file{*Compilation*} buffer.


@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.

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}.

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 machine 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.

@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 GNU Emacs 20, GNU Emacs 21
and GNU Emacs 22, as well as XEmacs 21.  XEmacs 20 is more
problematic, see the notes in @file{tramp.el}.  I don't think anybody
has really tried it on GNU Emacs 19.

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 NT/2000/XP @value{emacsname}.

There is some informations on @value{tramp} on NT at the following URL;
many thanks to Joe Stoy for providing the information:
@uref{ftp://ftp.comlab.ox.ac.uk/tmp/Joe.Stoy/}

@c The link is broken. I've contacted Tom for clarification. Michael.
@ignore
The above mostly contains patches to old ssh versions; Tom Roche has a
Web page with instructions:
@uref{http://www4.ncsu.edu/~tlroche/plinkTramp.html}
@end ignore

??? Is the XEmacs info correct?

??? Can somebody provide some information for getting it to work on NT
Emacs?  I think there was some issue with @command{ssh}?


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

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

@itemize @minus

@item
Unknown characters in the prompt

@value{tramp} needs to recognize the prompt on the remote machine
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.

@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.  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}.
@end itemize


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

When you log in to the remote machine, 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
machine 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
filename 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 `*.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-copy-beep-advice activate)
 " make tramp beep after copying a file."
 (interactive)
 (beep))
@end lisp


@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


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

Shame on you, why did you read until now?

@ifset emacs
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

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


@c For the developer
@node Version Control
@chapter The inner workings of remote version control
@cindex Version Control

Unlike @value{ftppackagename}, @value{tramp} has full shell access to the
remote machine. This makes it possible to provide version control for
files accessed under @value{tramp}.

The actual version control binaries must be installed on the remote
machine, accessible in the directories specified in
@var{tramp-remote-path}.

This transparent integration with the version control systems is one of
the most valuable features provided by @value{tramp}, but it is far from perfect.
Work is ongoing to improve the transparency of the system.

@menu
* Version Controlled Files::    Determining if a file is under version control.
* Remote Commands::             Executing the version control commands on the remote machine.
* Changed workfiles::           Detecting if the working file has changed.
* Checking out files::          Bringing the workfile out of the repository.
* Miscellaneous Version Control::  Things related to Version Control that don't fit elsewhere.
@end menu


@node Version Controlled Files
@section Determining if a file is under version control

The VC package uses the existence of on-disk revision control master
files to determine if a given file is under revision control. These file
tests happen on the remote machine through the standard @value{tramp} mechanisms.


@node Remote Commands
@section Executing the version control commands on the remote machine

There are no hooks provided by VC to allow intercepting of the version
control command execution. The calls occur through the
@code{call-process} mechanism, a function that is somewhat more
efficient than the @code{shell-command} function but that does not
provide hooks for remote execution of commands.

To work around this, the functions @code{vc-do-command} and
@code{vc-simple-command} have been advised to intercept requests for
operations on files accessed via @value{tramp}.

In the case of a remote file, the @code{shell-command} interface is
used, with some wrapper code, to provide the same functionality on the
remote machine as would be seen on the local machine.


@node Changed workfiles
@section Detecting if the working file has changed

As there is currently no way to get access to the mtime of a file on a
remote machine in a portable way, the @code{vc-workfile-unchanged-p}
function is advised to call an @value{tramp} specific function for remote files.

The @code{tramp-vc-workfile-unchanged-p} function uses the functioning VC
diff functionality to determine if any changes have occurred between the
workfile and the version control master.

This requires that a shell command be executed remotely, a process that
is notably heavier-weight than the mtime comparison used for local
files. Unfortunately, unless a portable solution to the issue is found,
this will remain the cost of remote version control.


@node Checking out files
@section Bringing the workfile out of the repository

VC will, by default, check for remote files and refuse to act on them
when checking out files from the repository. To work around this
problem, the function @code{vc-checkout} knows about @value{tramp} files and
allows version control to occur.


@node Miscellaneous Version Control
@section Things related to Version Control that don't fit elsewhere

Minor implementation details, &c.

@menu
* Remote File Ownership::       How VC determines who owns a workfile.
* Back-end Versions::           How VC determines what release your RCS is.
@end menu


@node Remote File Ownership
@subsection How VC determines who owns a workfile

@value{emacsname} provides the @code{user-full-name} function to
return the login name of the current user as well as mapping from
arbitrary user id values back to login names. The VC code uses this
functionality to map from the uid of the owner of a workfile to the
login name in some circumstances.

This will not, for obvious reasons, work if the remote system has a
different set of logins. As such, it is necessary to delegate to the
remote machine the job of determining the login name associated with a
uid.

Unfortunately, with the profusion of distributed management systems such
as @code{NIS}, @code{NIS+} and @code{NetInfo}, there is no simple,
reliable and portable method for performing this mapping.

Thankfully, the only place in the VC code that depends on the mapping of
a uid to a login name is the @code{vc-file-owner} function. This returns
the login of the owner of the file as a string.

This function has been advised to use the output of @command{ls} on the
remote machine to determine the login name, delegating the problem of
mapping the uid to the login to the remote system which should know more
about it than I do.


@node Back-end Versions
@subsection How VC determines what release your RCS is

VC needs to know what release your revision control binaries you are
running as not all features VC supports are available with older
versions of @command{rcs(1)}, @command{cvs(1)} or @command{sccs(1)}.

The default implementation of VC determines this value the first time it
is needed and then stores the value globally to avoid the overhead of
executing a process and parsing its output each time the information is
needed.

Unfortunately, life is not quite so easy when remote version control
comes into the picture. Each remote machine may have a different version
of the version control tools and, while this is painful, we need to
ensure that unavailable features are not used remotely.

To resolve this issue, @value{tramp} currently takes the sledgehammer
approach of making the release values of the revision control tools
local to each @value{tramp} buffer, forcing VC to determine these values
again each time a new file is visited.

This has, quite obviously, some performance implications. Thankfully,
most of the common operations performed by VC do not actually require
that the remote version be known. This makes the problem far less
apparent.

Eventually these values will be captured by @value{tramp} on a system by
system basis and the results cached to improve performance.


@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.
@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 filename, 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.


@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 @value{tramp} does not work on XEmacs 20.

This is because it requires the macro @code{with-timeout} which does not
appear to exist in XEmacs 20.  I'm somewhat reluctant to add an
emulation macro to @value{tramp}, but if somebody who uses XEmacs 20 steps
forward and wishes to implement and test it, please contact me or the
mailing list.

@item The @value{tramp} filename syntax differs between GNU Emacs and XEmacs.

The GNU Emacs maintainers wish to use a unified filename 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
filename 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 filenames were unified, @value{tramp}
would have to be installed from the start, too.

@ifset xemacs
@strong{Note:} If you'ld 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{.../xemacs-packages/lisp/tramp/auto-autoloads.el*}.

In case of unified filenames, 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 filenames is described in the @value{tramp} manual
for @value{emacsothername}.
@end ifset
@end itemize

@node Concept Index
@comment node-name,    next,  previous,      up
@unnumbered Concept Index
@printindex cp
@contents
@c End of tramp.texi - the TRAMP User Manual
@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 * Mention that bookmarks are a cool feature to go along with Tramp.
@c * Make terminology "inline" vs "out-of-band" consistent.
@c   It seems that "external" is also used instead of "out-of-band".

@c * M. Albinus
@c ** Use `filename' resp. `file name' consistently.
@c ** Use `host' resp. `machine' consistently.
@c ** Consistent small or capitalized words especially in menues.

@ignore
   arch-tag: f96dd66e-6dd3-4c92-8d77-9c56205ba808
@end ignore