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 Version values, for easy modification
@c NOTE: The 'UPDATED' value is updated by the 'time-stamp' function.
@c       If you change it by hand, the modifications will not stay.
@set VERSION $Revision: 1.2 $
@set UPDATED Monday, 17 June, 2002


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

@c Macro to make formatting of the tramp program name consistent.
@macro tramp
@sc{tramp}
@end macro

@c Copying permissions, et al
@ifinfo
This file documents @tramp{}, a remote file editing package for Emacs and
XEmacs.
     
Copyright @copyright{} 1999, 2000 Free Software Foundation, Inc.
     
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
     
@ignore 
Permission is granted to process this file through TeX and print the
results, provided the printed document carries a copying permission
notice identical to this one except for the removal of this paragraph
(this paragraph not being relevant to the printed manual).
   
@end ignore
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided also that the
sections entitled ``Copying'' and ``GNU General Public License'' are
included exactly as in the original, and provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.
     
Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be stated in a translation
approved by the Free Software Foundation.
@end ifinfo

@tex

@titlepage
@title @tramp{} User Manual
@subtitle Last updated @value{UPDATED}

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

@vskip 0pt plus 1filll
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
     
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided also that the
sections entitled ``Copying'' and ``GNU General Public License'' are
included exactly as in the original, and provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.
     
Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be stated in a translation
approved by the Free Software Foundation.

@end titlepage
@page

@end tex

@ifnottex
@node Top, Copying, (dir), (dir)
@top @tramp{} User Manual

@tramp{} stands for `Transparent Remote (file) Access, Multiple
Protocol'.  This package provides remote file editing, similar to
@cite{ange-ftp} and @cite{EFS}.

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

This is version @value{VERSION} of the @tramp{} manual, last updated on
@value{UPDATED}.

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

@ifhtml
This manual is also available as a @uref{tramp_ja.html, Japanese
translation}.

The latest release of @tramp{} is available for
@uref{http://savannah.gnu.org/download/tramp/,
download}, or you may see @ref{Obtaining @tramp{}} for more details,
including the CVS server details.

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

There is a mailing list for @tramp{}, available at
@email{tramp-devel@@mail.freesoftware.fsf.org}, and archived at
@uref{http://www.mail-archive.com/emacs-rcp@@ls6.cs.uni-dortmund.de/} as
well as the usual Savannah archives.

@end ifnottex

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

For the end user:
* Obtaining @tramp{}::          How to obtain @tramp{}.
* History::                     History of @tramp{}
* Installation::                Installing @tramp{} with your (X)Emacs.
* Configuration::               Configuring @tramp{} for use.
* Usage::                       An overview of the operation of @tramp{}.
* Bug Reports::                 Reporting Bugs and Problems
* Frequently Asked Questions::  Questions and answers from the mailing list.

For the developer:
* Version Control::             The inner workings of remote version control.
* Files directories and paths::  How file names, directories and paths are mangled and managed.
* Issues::                      

@detailmenu
 --- The Detailed Node Listing ---

Configuring @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.
* Remote Programs::             How @tramp{} finds and uses programs on the remote machine.
* Remote shell setup::          

Using @tramp

* Filename Syntax::             @tramp{} filename conventions.
* Multi-hop filename syntax::   Multi-hop filename conventions
* Dired::                       Dired and filename completion.

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 paths are mangled and managed.

* Path deconstruction::         Breaking a path into its components.

@end detailmenu
@end menu

@node Copying
@chapter @tramp{} Copying conditions

Copyright (C) 1998, 1999, 2000 Free Software Foundation, Inc.

tramp.el is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 2, or (at your option) any later
version.

tramp.el is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
more details.

You should have received a copy of the GNU General Public License along
with GNU Emacs; see the file COPYING. If not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
USA.


@node Overview
@chapter An overview of @tramp

After the installation of @tramp{} into your Emacs, 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
@command{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 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 @tramp{} requires only that the
remote login is possible and is carried out at the terminal. In order to
access remote files @tramp{} needs to transfer their content to the local
machine temporarily.

@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 rely on a remote file transfer package such
as @command{rcp}, @command{scp} or @command{rsync}. The use of these
methods is only possible if the file copy command does not ask for a
password for the remote machine.

If the remote copy methods are not suitable for you, @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.

Within these limitations, @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.

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


@subsubheading Behind the scenes

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

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

@itemize
@item
@tramp{} discovers that it needs a connection to the host. So it invokes
@command{telnet HOST} or @command{rsh HOST -l USER} or a similar tool to
connect to the remote host. Communication with this process happens
through an Emacs 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 @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).
@tramp{} displays the prompt in the minibuffer, asking you for the
password or pass phrase.

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

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

If @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 @tramp{} sees a `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 @tramp{} sees the shell prompt
from the remote host.  Now @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 @command{exec /bin/sh} as a valid command.
Maybe you use the Scheme shell @command{scsh}@dots{}}

After the Bourne shell has come up, @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 @tramp{} tries to find out what files exist
on the remote host so that it can do filename completion.

So, @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 @tramp{} transfers the file contents.

For inline transfers, @tramp{} issues a command like @command{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, @tramp{} issues a command like @command{rcp
user@@host:/path/to/remote/file /tmp/tramp.4711} and 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, @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 @tramp{}.


@c For the end user
@node Obtaining @tramp{}
@chapter Obtaining @tramp{}.

@tramp{} is freely available on the Internet and the latest release may be
downloaded from
@uref{ftp://ls6-ftp.cs.uni-dortmund.de/pub/src/emacs/tramp.tar.gz}. This
release includes the full documentation and code for @tramp{}, suitable
for installation.

For the especially brave, @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 @tramp{}
from CVS can be found by going to the Savannah project page at
@uref{http://savannah.gnu.org/projects/tramp/} and then clicking on the
CVS link in the navigation bar at the top.  Or follow the example
session below:

@example
] @strong{cd ~/lisp}
] @strong{cvs -d:pserver:anoncvs@@subversions.gnu.org:/cvsroot/tramp login}

(Logging in to anoncvs@@subversions.gnu.org)
CVS password: @strong{(just hit RET here)}
@dots{}

] @strong{cvs -z3 -d:pserver:anoncvs@@subversions.gnu.org:/cvsroot/tramp co tramp}
@end example

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

@example
] @strong{cd ~/lisp/tramp}
] @strong{cvs update -d}
@end example


@node History
@chapter History of @tramp{}

Development was started end of November 1998.  The package was called
`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
`rcp.el', and now it's @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 a major feature was the multi-hop methods
added in April 2000.


@node Installation
@chapter Installing @tramp{} into Emacs or XEmacs

Installing @tramp{} into your Emacs or XEmacs is a relatively easy
process, at least compared to rebuilding your machine from scratch. ;)

Seriously though, the installation should be a fairly simple matter.

The easiest way to proceed is as follows:

@itemize
@item
Choose a directory, say @file{~/emacs/}.  Change into that directory and
unpack the tarball.  This will give you a directory
@file{~/emacs/tramp/} which contains subdirectories @file{lisp} for the
Lisp code and @file{texi} for the documentation.

@item
Optionally byte-compile all files in the Lisp directory,
@file{~/emacs/tramp/lisp/}, by issuing a command like the following from
the top level directory @file{~/emacs/tramp/}:
@example
make EMACS=emacs all            # for Emacs users
make EMACS=xemacs all           # for XEmacs users
@end example

@item
NOTE:
@example
If you run into problems running the example @command{make}
commands, don't dispare.  You can still byte compile the
@file{*.el} files by opening emacs in @command{dired}
(@command{C-x d}) mode, at @file{~/tramp/lisp}.  Mark the lisp
files with @command{m}, then press @command{B} to byte compile
your selections.

Something similar can be done to create the info manual.  
Just cd to @file{~/emacs/tramp/texi} and load the @file{tramp.texi}
file in emacs.  Then press @command{M-x makeinfo-buffer <RET>}
to generate @file{tramp.info}.
@end example     

@item
Tell Emacs about the new Lisp directory and the @tramp{} package 
with the following lines in @file{~/.emacs}:
@lisp
(add-to-list 'load-path "~/emacs/tramp/lisp/")
(require 'tramp)
@end lisp

@item
To be able to read the Info documentation, create a file
@file{~/emacs/tramp/texi/dir} using for example the
@command{install-info} command, and add the directory to the search 
path for Info.

@item
NOTE:
@example
On systems using `gnu' @command{install-info}, the
@command{install-info} syntax is very direct and simple.  One can 
cd to @file{~/emacs/tramp/texi} and type:
    @command{install-info tramp.info dir}
and a @file{dir} file will be created with the @tramp{}
entry.  The info reader will know how to interpret it, but must
be told where to find it (see below).  If you want anything fancier
you'll need to look through @command{man install-info}.

Debian gnu/linux doesn't default to `gnu' @command{install-info} and
uses its own version.  This version does not create a @file{dir} file
for you from scratch.  You must provide a skeleton dir file it
recognizes.  One can be found in a default install at
@file{/usr/info/dir}.  Copy the top of this file down to the first
occurrence of `* Menu' including that line plus one more blank line,
to your working directory @file{texi/dir}, or use the sample provided
in the @file{texi} directroy of this distribution.  See
@file{texi/dir_sample}

Once a @file{dir} file is in place, this command will make the entry.
     install-info --infodir=. tramp.info
If you want it in a specific category
   (see @command{man install-info} for further details)
@end example

If the environment variable @env{INFOPATH} is set, add the directory
@file{~/emacs/tramp/texi/} to it.  Else, add the directory to
@code{Info-default-directory-list}, as follows:
@lisp
(add-to-list 'Info-default-directory-list "~/emacs/tramp/texi/")
@end lisp
XEmacs 21 users should use @code{Info-directory-list} rather than
@code{Info-default-directory-list}.

@end itemize


For XEmacs users, the package @command{fsf-compat} must be installed.
For details on package installation, see @ref{Packages, , ,xemacs}.
@ifhtml
(If the previous link doesn't work, try the XEmacs documentation at
@uref{http://www.xemacs.org/Documentation/packageGuide.html,the XEmacs
site}.)
@end ifhtml

@node Configuration
@chapter Configuring @tramp{} for use

@tramp{} is (normally) fully functional when it is initially
installed. It is initially configured to use the @command{rsh} and
@command{rcp} programs to connect to the remote host.

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 @tramp
uses. There are several different methods that @tramp{} can use to
connect to remote machines and transfer files (@pxref{Connection types}).


@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.
* Customizing Methods::         Using Non-Standard Methods.
* Remote Programs::             How @tramp{} finds and uses programs on the remote machine.
* Remote shell setup::          Remote shell setup hints.
* Windows setup hints::         Issues with Cygwin ssh.
@end menu


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

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 @tramp
requires to make the remote file system transparently accessible from
the local machine. It is only when visiting files that the methods
differ.

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{external transfer methods}.

The performance of the external transfer methods is generally better
than that of the inline methods.  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 do require that the remote copy command is not
interactive --- that is, the command does not prompt you for a password.
If you cannot perform remote copies without a password, you will need to
use an inline transfer method to work with @tramp{}.

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

The inline methods in @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, @tramp{} may be able to use
features of Emacs to decode and encode the files or it may require
access to external commands to perform that task.

@tramp{} supports the use of @command{uuencode} to transfer files. This is
@emph{not} recommended. The @command{uuencode} and @command{uudecode}
commands are not well standardized and may not function correctly or at
all on some machines, notably AIX and IRIX. These systems do not work
with @command{uuencode} at all.  (But do see the note about AIX in the
documentation for @var{tramp-methods}.)

In summary, if possible use the @command{mimencode} methods to transfer
the data base64 encoded. This has the advantage of using a built-in
command in every modern Emacs, improving performance.

@itemize
@item @option{rm}  ---  @command{rsh} with @command{mimencode}

Connect to the remote host with @command{rsh} and use base64 encoding to
transfer files between the machines.

This requires the @command{mimencode} command that is part of the
@command{metamail} packages. This may not be installed on all remote
machines.


@item @option{sm}  ---  @command{ssh} with @command{mimencode}

Connect to the remote host with @command{ssh} and use base64 encoding to
transfer files between the machines.

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{sm1} and @option{sm2} that use the
@command{ssh1} and @command{ssh2} commands explicitly. If you don't know
what these are, you do not need these options.


@item @option{tm}  ---  @command{telnet} with @command{mimencode}

Connect to the remote host with @command{telnet} and use base64 encoding
to transfer files between the machines.

This requires the @command{mimencode} command that is part of the
@command{metamail} packages.


@item @option{ru}  ---  @command{rsh} with @command{uuencode}

Connect to the remote host with @command{rsh} and use the
@command{uuencode} and @command{uudecode} commands to transfer files
between the machines.


@item @option{su}  ---  @command{ssh} with @command{uuencode}

Connect to the remote host with @command{ssh} and use the
@command{uuencode} and @command{uudecode} commands to transfer files
between the machines.

As with the @command{ssh} and base64 option above, this provides the
@option{su1} and @option{su2} methods to explicitly select an ssh
version.

Note that this method does not invoke the @command{su} program, see
below for methods which use that.


@item @option{tu}  ---  @command{telnet} with @command{uuencode}

Connect to the remote host with @command{telnet} and use the
@command{uuencode} and @command{uudecode} commands to transfer files
between the machines.


@item @option{sum} --- @command{su} with @command{mimencode}

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.  Uses
base64 encoding to transfer the file contents.


@item @option{suu} --- @command{su} with @command{uuencode}

Like @option{sum}, this uses the @command{su} program to allow you to
edit files on the local host as another user.  Uses @command{uuencode}
and @command{uudecode} to transfer the file contents.


@item @option{sudm} --- @command{sudo} with @command{mimencode}

This is similar to the @option{sum} 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{sudu} --- @command{sudo} with @command{uuencode}

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


@item @option{smx} --- @command{ssh} with @command{mimencode}

As you expect, this is similar to @option{sm}, only a little
different.  Whereas @option{sm} opens a normal interactive shell on
the remote host, this option uses @command{ssh -t -t HOST -l USER
/bin/sh} tp 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
@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 Emacs 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 @tramp{} mightily.


@item @option{km} --- @command{krlogin} with @command{mimencode}

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


@item @option{plinku} --- @command{plink} with @command{uuencode}

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

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?

@item @option{plinkm} --- @command{plink} with @command{mimencode}

Like @option{plinku}, but uses base64 encoding instead of uu encoding.

@end itemize



@node External transfer methods
@section External transfer 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 @emph{must} be able
to execute the transfer utility to copy files to and from the remote
machine without any interaction.

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 @command{scp} to run without asking for a password but
would still like to use @command{ssh} to secure your connection, have a
look at the @command{ssh} based inline methods.


@itemize
@item @option{rcp}  ---  @command{rsh} and @command{rcp}

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.


@item @option{scp}  ---  @command{ssh} and @command{scp}

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.


@item @option{rsync}  ---  @command{ssh} and @command{rsync}

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. 


@item @option{scpx} --- @command{ssh} and @command{scp}

As you 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 @command{ssh -t -t HOST -l 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 @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 Emacs 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 @tramp{} mightily.


@item @option{pscp} --- @command{plink} and @command{pscp}

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.


@item @option{fcp} --- @command{fsh} and @command{fcp}

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 @command{fsh HOST -l USER /bin/sh -i} to
establish the connection, it does not work to just say @command{fsh
HOST -l USER}.

@end itemize

@node Multi-hop Methods
@section Connecting to a remote host using multiple hops

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
@tramp{} methods.

A multi-hop file name specifies a method, a number of hops, and a path
name on the remote system.  The method specifies how the file is
transferred through the inline connection.  The following two multi-hop
methods are available:

@itemize
@item @option{multi} --- base64 encoding with @command{mimencode}

The file is transferred through the connection in base64 encoding.  Uses
the @command{mimencode} program for doing encoding and decoding, but
uses an Emacs internal implementation on the local host if available.

@item @option{multiu} --- use commands @command{uuencode} and @command{uudecode}

The file is transferred through the connection in `uu' encoding.  Uses
the @command{uuencode} and @command{uudecode} programs for encoding and
decoding, but uses a Lisp implementation for decoding on the local host
if available.

@end itemize

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

@itemize
@item @option{telnet}

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 @option{rsh}

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

@item @option{ssh}

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

@item @option{su}

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 a
@option{su} hop, the host name is ignored and only the user name is
used.

@item @option{sudo}

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

@end itemize

Some people might wish to use port forwarding with @code{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 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 a @code{sshf} hop which connects to port 4400 instead of
the standard port.


@node Default Method
@section Selecting a default method

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

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

External transfer methods are normally preferable to inline transfer
methods, giving better performance. They may not be useful if you use
many remote machines where you cannot log in without a password.

@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 @command{rsh} and @command{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 @command{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.

@node Customizing Methods
@section Using Non-Standard 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 Remote Programs
@section How @tramp{} finds and uses programs on the remote machine.

@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.

When @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 @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 @tramp{} when you connect and the software
found.

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

@example
(require 'tramp)                @i{; @tramp{} must be loaded before this}
                                @i{; happens.}

@i{; We have @command{perl} in "/usr/local/perl"}
(add-to-list 'tramp-remote-path "/usr/local/perl")
@end example

@node Remote shell setup
@comment  node-name,  next,  previous,  up
@section Remote shell setup hints

As explained in the @ref{Overview} section, @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 birthdate of your mother; clearly @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 @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 @tramp{} expect.  This might
be inconvenient because you have to invest a lot of effort into shell
setup before you can begin to use @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 exist, and
therefore it tries different possibilities.  (On some hosts and shells,
the command @code{test -e} does the trick, on some hosts the shell
builtin doesn't work but the program @code{/usr/bin/test -e} or
@code{/bin/test -e} works.  And on still other hosts, @code{ls -d} is
the right way to do this.)

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

@itemize
@item @code{shell-prompt-pattern}

@vindex shell-prompt-pattern
After logging in to the remote host, @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.

@item @code{tset} and other questions

Some people invoke the @code{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.  @tramp{} does
not know how to answer these questions.  (A facility for enabling
@tramp{} to answer these questions is planned for some future version,
but don't hold your breath.)

Therefore, you should take care that the shell does not ask any
questions when invoked from @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
@code{dumb}.

@end itemize


@node Windows setup hints
@section Issues with Cygwin ssh

This section needs a lot of work!  Please help.

If you use the Cygwin installation of ssh (you have to explicitly select
it in the installer), then it should work out of the box to just select
@code{smx} as the connection method.  You can find information about
setting up Cygwin in their FAQ at @uref{http://cygwin.com/faq/}.


@node Usage
@chapter Using @tramp

Once you have installed @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 @tramp{} using a formalized syntax specifying the
details of the system to connect to. This is similar to the syntax used
by the @command{EFS} and @command{ange-ftp} packages.


@menu
* Filename Syntax::             @tramp{} filename conventions.
* Multi-hop filename syntax::   Multi-hop filename conventions
* Dired::                       Dired and filename completion.
@end menu


@node Filename Syntax
@section @tramp{} filename conventions

To access the file <path> on the remote machine <machine> you would
specify the filename @file{/[<machine>]<path>}.  (The square brackets
are part of the file name.)  This will connect to <machine> and transfer
the file using the default method.  @xref{Default Method}.

Some examples of @tramp{} filenames are:

@table @file
@item /[melancholia].emacs
Edit the file @file{.emacs} in your home directory on the machine
@code{melancholia}.

@item /[melancholia.danann.net].emacs
This edits the same file, using the fully qualified domain name of
the machine.

@item /[melancholia]~/.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 /[melancholia]~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 /[melancholia]/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, @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{/[<user>@@<machine>]/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{/[daniel@@melancholia].emacs}.


It is also possible to specify other file transfer methods
(@pxref{Default Method}) as part of the filename.  This is done by
replacing the initial @file{/[} with @file{/[<method>/}.  (Note the
trailing slash!)  The user, machine and file specification remain the
same.

So, to connect to the machine @code{melancholia} as @code{daniel}, using
the @option{su} method to transfer files, and edit @file{.emacs} in my
home directory I would specify the filename
@file{/[su/daniel@@melancholia].emacs}.


@node Multi-hop filename syntax
@section Multi-hop filename conventions

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

@file{/[multi/rsh:out@@gate/telnet:kai@@real.host]/path/to.file}

This is quite a mouthful.  So let's go through it step by step.  The
file name consists of three parts, separated by slashes and square
brackets.  The first part is @file{/[multi}, the method specification.
The second part is @file{rsh:out@@gate/telnet:kai@@real.host} and
specifies the hops.  (Yes, the second part may contain even more
slashes, so that's why this file name has more than two colons in it.)
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.  @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:out@@gate} and
@file{telnet: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: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: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 @var{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 Dired
@section Dired and filename completion

@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.

Filename completion also works with @tramp{} for files on remote machines
although there is no completion for user names or machine names at this
stage.

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

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 Bug Reports
@chapter Reporting Bugs and Problems

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

The @tramp{} mailing list is a great place to get information on working
with @tramp{}, solving problems and general discussion and advice on topics
relating to the package.

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

For help on subscribing to the list, send mail to the administrative
address, @email{tramp-devel-request@@mail.freesoftware.fsf.org}, with the
subject @samp{help}.

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

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

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

@tramp{} is available at
@uref{ftp://ls6-ftp.cs.uni-dortmund.de/pub/src/emacs/tramp.tar.gz}.
There is also a Savannah project page, at
@uref{https://savannah.gnu.org/projects/tramp/}.


@item Which systems does it work on?

The package has been used successfully on Emacs 20 and Emacs 21, 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 Emacs 19.

The package was intended to work on Unix, and it really expects a
Unix-like system on the remote end, but some people seemed to have some
success getting it to work on NT Emacs.

There are some informations on 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/}

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}

??? 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 I can't stop EFS starting with XEmacs

Not all the older versions of @tramp{} supported XEmacs correctly. The
first thing to do is to make sure that you have the latest version of
@tramp{} installed.

If you do, please try and find out exactly the conditions required for
the @code{EFS} handlers to fire. If you can, putting a breakpoint on
@code{efs-ftp-path} and sending in the stack trace along with your bug
report would make it easier for the developers to work out what is going
wrong.


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


@item File name completion does not work in large directories

@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 shell
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 @command{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 What kinds of systems does @tramp{} work on

@tramp{} really expects the remote system to be a Unix-like system.  The
local system should preferably be Unix-like, as well, but @tramp{} might
work on NT with some tweaking.


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

The following snippet can be put in your @file{~/.emacs} file.  It makes
Emacs 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, @tramp{} starts @code{ksh} on the remote host for tilde
expansion.  Maybe @code{ksh} saves the history by default.  @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

@end itemize


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

Unlike EFS and ange-ftp, @tramp{} has full shell access to the remote
machine. This makes it possible to provide version control for files
accessed under @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 @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 @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 @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 @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 @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

Emacs 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, @tramp{} currently takes the sledgehammer
approach of making the release values of the revision control tools
local to each @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 @tramp{} on a system by
system basis and the results cached to improve performance.


@node Files directories and paths
@chapter How file names, directories and paths are mangled and managed.

@menu
* Path deconstruction::         Breaking a path into its components.
@end menu


@node Path deconstruction
@section Breaking a path into its components.

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

Their replacements are reasonably simplistic in their approach. They
dissect the filename, call the original handler on the remote path and
then rebuild the @tramp{} path with the result.

This allows the platform specific hacks in the original handlers to take
effect while preserving the @tramp{} path 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 @tramp{}, the encoding and decoding programs need to
read from stdin and write to stdout.  On some systems, @code{uudecode -o
-} will read stdin and write the decoded file to stdout, on other
systems @code{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
@code{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 @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 @tramp{}, but if somebody who uses XEmacs 20 steps
forward and wishes to implement and test it, please contact me or the
mailing list.

@end itemize


@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 Local Variables:
@c eval: (add-hook 'write-file-functions 'time-stamp)
@c time-stamp-start: "@set UPDATED "
@c time-stamp-format: "%:a, %:d %:b, %:y"
@c time-stamp-end: "$"
@c time-stamp-line-limit: 50
@c End: