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tramp version 2.1.8 User Manual

This file documents tramp version 2.1.8, a remote file editing package for GNU Emacs.

tramp stands for `Transparent Remote (file) Access, Multiple Protocol'. This package provides remote file editing, similar to Ange-FTP.

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

You can find the latest version of this document on the web at

The manual has been generated for GNU Emacs. If you're using the other Emacs flavor, you should read the XEmacs pages.

This manual is also available as a Japanese translation.

The latest release of tramp is available for download, or you may see Obtaining Tramp for more details, including the CVS server details.

tramp also has a Savannah Project Page.

There is a mailing list for tramp, available at, and archived at the tramp Mail Archive. Older archives are located at SourceForge Mail Archive and The Mail Archive.

Copyright © 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.

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.

For the end user:

For the developer:

--- The Detailed Node Listing ---

Installing tramp with your GNU Emacs

Configuring tramp for use

Using tramp

The inner workings of remote version control

Things related to Version Control that don't fit elsewhere

How file names, directories and localnames are mangled and managed

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1 An overview of tramp

After the installation of tramp into your GNU 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 dired are transparently enabled.

Your access to the remote machine can be with the rsh, rlogin, 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 ssh connections out of the box, one of the more common uses of the package. This allows relatively secure access to machines, especially if 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 (for large files) rely on a remote file transfer package such as rcp, scp or rsync.

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 mimencode or uuencode tools are available on the remote machine. These methods are generally faster for small files.

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. See Bug Reports.

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

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

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2 Obtaining Tramp.

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

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 the following URL and then clicking on the CVS link in the navigation bar at the top.

Or follow the example session below:

     ] cd ~/emacs
     ] export CVS_RSH="ssh"
     ] cvs -z3 co tramp

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

     ] cd ~/emacs/tramp
     ] export CVS_RSH="ssh"
     ] cvs update -d

Once you've got updated files from the CVS repository, you need to run autoconf in order to get an up-to-date configure script:

     ] cd ~/emacs/tramp
     ] autoconf

People who have no direct CVS access (maybe because sitting behind a blocking firewall), can try the Nightly CVS Tree Tarball instead of.

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3 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 ssh to log in to a remote host and using 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 major features were the multi-hop methods added in April 2000 and the unification of tramp and Ange-FTP filenames in July 2002. In July 2004, multi-hop methods have been replaced by proxy hosts. Running commands on remote hosts was introduced in December 2005.

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4 Installing tramp into GNU Emacs.

If you use the version that comes with your GNU Emacs, the following information is not necessary. Installing tramp into your GNU Emacs 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:

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4.1 Parameters in order to control installation.

There are some Lisp packages which are not contained in older GNU Emacsen by default yet. In order to make a link for them into Tramp's contrib directory, you must use the --with-contrib option:

     ./configure --with-contrib

By default, make install will install tramp's files in /usr/local/share/emacs/site-lisp and /usr/local/share/info. You can specify an installation prefix other than /usr/local by giving configure the option --prefix=PATH. On GNU/Linux systems, it has been reported useful to apply

     ./configure --prefix=/usr

If your installed copy of GNU Emacs is named something other than emacs, you will need to tell `make' where to find it so that it can correctly byte-compile the tramp sources.

For example, to force the use of XEmacs you might do this:

     ./configure --with-xemacs

You can even pass the GNU Emacs or XEmacs command to be called:

     ./configure --with-xemacs=xemacs21

The syntax of tramp file names is different for GNU Emacs and XEmacs. The Info manual will be generated for the Emacs flavor choosen in the configure phase. If you want the Info manual for the other version, you need to set the variable EMACS_INFO to make:

     ./configure --with-emacs
     make EMACS_INFO=xemacs

Also, the --prefix=PATH option to configure may not be general enough to set the paths you want. If not, you can declare the directories Lisp and Info files should be installed.

For example, to put the Lisp files in ~/elisp and the Info file in ~/info, you would type:

     ./configure --with-lispdir=$HOME/elisp --infodir=$HOME/info

On MS Windows, given Emacs is installed at C:/Program Files/Emacs, you should apply

     ./configure --with-lispdir='C:/Program Files/Emacs/site-lisp' \
                 --infodir='C:/Program Files/Emacs/info'

make supports the DESTDIR variable for staged installation; see Command Variables:

     make DESTDIR=/tmp install

Running configure might result in errors or warnings. The output explains in detail what's going wrong.

In case of errors, it is mandatory to fix them before continuation. This can be missing or wrong versions of emacs, GNU Emacs packages, make, or makeinfo.

Warnings let configure (and the whole installation process) continue, but parts of Tramp aren't installed. This can happen with missing or wrong versions of texi2dvi or install-info. Here you can decide yourself whether you want to renounce on the related feature (tramp.dvi file for printed output, Tramp entry in Info's dir file), or whether you want to adapt your $PATH environment variable, and rerun configure. An alternative is calling the missed parts manually later on.

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4.2 How to plug-in tramp into your environment.

If you don't install tramp into the intended directories, but prefer to use from the source directory, you need to add the following lines into your .emacs:

     (add-to-list 'load-path "~/emacs/tramp/lisp/")
     (require 'tramp)

If the environment variable INFOPATH is set, add the directory ~/emacs/tramp/info/ to it. Else, add the directory to Info-default-directory-list, as follows:

     (add-to-list 'Info-default-directory-list "~/emacs/tramp/info/")

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4.3 Japanese manual.

Thanks to Yoichi Nakayama, there exists a japanese translation of the tramp manual. You can generate it applying the --with-japanese-manual option:

     ./configure --with-japanese-manual

This will result in an Info manual see Top.

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5 Configuring tramp for use

tramp is (normally) fully functional when it is initially installed. It is initially configured to use the scp program to connect to the remote host. So in the easiest case, you just type C-x C-f and then enter the filename /user@machine:/path/to.file.

On some hosts, there are problems with opening a connection. These are related to the behavior of the remote shell. See See 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 (see Connection types).

If you don't know which method is right for you, see See Default Method.

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5.1 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 rsh, ssh or 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 rcp, scp or rsync. The former are called inline methods, the latter are called out-of-band methods or external transfer methods (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 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 ssh-agent, or such alike). Modern scp implementations offer options to reuse existing ssh connections, see method scpc. If it isn't possible, you should consider Password caching, otherwise you will be prompted for a password every copy action.

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5.2 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 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 GNU Emacs to decode and encode the files or it may require access to external commands to perform that task.

tramp checks the availability and usability of commands like mimencode (part of the metamail package) or uuencode on the remote host. The first reliable command will be used. The search path can be customized, see Remote Programs.

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

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

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

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

There are also two variants, ssh1 and ssh2, that call `ssh -1' and `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 ~/.ssh/config, the SSH configuration file, which protocol should be used, and use the regular ssh method.)

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

All the methods based on ssh have an additional kludgy feature: you can specify a host name which looks like 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 -p 42 as arguments to the ssh command.

Connect to the remote host with telnet. This is as unsecure as the rsh method.
This method does not connect to a remote host at all, rather it uses the su program to allow you to edit files as another user. With other words, a specified host name in the file name is silently ignored.
This is similar to the su method, but it uses sudo rather than su to become a different user.

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

As you would expect, this is similar to ssh, only a little different. Whereas ssh opens a normal interactive shell on the remote host, this option uses `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.

Note that this procedure does not eliminate questions asked by ssh itself. For example, ssh might ask “Are you sure you want to continue connecting?” if the host key of the remote host is not known. 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 ssh, when invoked from an GNU 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. For reasons unknown, some Windows ports for ssh require the doubled `-t' option.

This supports the `-p' kludge.

This method is also similar to ssh. It only uses the krlogin -x command to log in to the remote host.
This method is mostly interesting for Windows users using the PuTTY implementation of SSH. It uses `plink -ssh' to log in to the remote host.

This supports the `-P' kludge.

Additionally, the methods plink1 and plink2 are provided, which call `plink -1 -ssh' or `plink -2 -ssh' in order to use SSH protocol version 1 or 2 explicitly.

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: Say something about the first shell command failing. This might be due to a wrong setting of tramp-rsh-end-of-line.

This is an experimental implementation of the fish protocol, known from the GNU Midnight Commander or the KDE Konqueror. tramp expects the fish server implementation from the KDE kioslave. That means, the file ~/ is expected to reside on the remote host.

The implementation lacks good performance. The code is offered anyway, maybe somebody can improve the performance.

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5.3 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.

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

rcprsh and rcp
This method uses the rsh and rcp commands to connect to the remote machine and transfer files. This is probably the fastest connection method available.

The alternative method remcp uses the remsh and rcp commands. It should be applied on machines where remsh is used instead of rsh.

scpssh and scp
Using ssh to connect to the remote host and 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 scp session can begin to absorb the advantage that the lack of encoding and decoding presents.

There are also two variants, scp1 and scp2, that call `ssh -1' and `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 ~/.ssh/config, the SSH configuration file, which protocol should be used, and use the regular scp method.)

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

All the ssh based methods support the kludgy `-p' feature where you can specify a port number to connect to in the host name. For example, the host name host#42 tells tramp to specify `-p 42' in the argument list for ssh, and to specify `-P 42' in the argument list for scp.

sftpssh and sftp
That is mostly the same method as scp, but using sftp as transfer command. So the same remarks are valid.

This command does not work like Ange-FTP, where ftp is called interactively, and all commands are send from within this session. Instead of, ssh is used for login.

This method supports the `-p' hack.

rsyncssh and rsync
Using the ssh command to connect securely to the remote machine and the rsync command to transfer files is almost identical to the scp method.

While rsync performs much better than 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 rsync based method may be considerably faster than the 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 `-p' hack.

scpxssh and scp
As you would expect, this is similar to scp, only a little different. Whereas scp opens a normal interactive shell on the remote host, this option uses `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 ssh, when invoked from an GNU 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.

This method supports the `-p' hack.

scpcssh and scp
Newer versions of ssh (for example OpenSSH 4) offer an option ControlMaster. This allows scp to reuse an existing ssh channel, which increases performance.

Before you use this method, you shall check whether your ssh implementation does support this option. Try from the command line

          ssh localhost -o ControlMaster=yes

This method supports the `-p' hack.

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

This method supports the `-P' hack.

psftpplink and psftp
As you would expect, this method is similar to sftp, but it uses the plink command to connect to the remote host, and it uses psftp for transferring the files. These programs are part of PuTTY, an SSH implementation for Windows.

This method supports the `-P' hack.

fcpfsh and fcp
This method is similar to scp, but it uses the fsh command to connect to the remote host, and it uses fcp for transferring the files. fsh/fcp are a front-end for ssh which allow for reusing the same ssh session for submitting several commands. This avoids the startup overhead of 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 `fsh host -l user /bin/sh -i' to establish the connection, it does not work to just say fsh host -l user.

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

This is not a native tramp method. Instead of, it forwards all requests to Ange-FTP.
This is another not natural tramp method. It uses the 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 $ character in which default shares usually end, must be written $$ due to environment variable substitution in file names. If no share name is given (i.e. remote directory /), 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 Password caching.

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

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

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

The smb method supports the `-p' hack.

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

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5.4 Selecting a default method

When you select an appropriate transfer method for your typical usage you should set the variable 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 name. For example:

     (setq tramp-default-method "ssh")

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

     (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"))

See the documentation for the variable tramp-default-method-alist for more details.

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

See Inline methods. See External transfer 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 rsh and 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 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.

5.4.1 Which method is the right one for me?

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 ...

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 ssh. So I suggest that you use the ssh method. So, type C-x C-f /ssh:root@otherhost:/etc/motd <RET> to edit the /etc/motd file on the other host.

If you can't use 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 plink method which uses the PuTTY implementation of ssh. Or you use Kerberos and thus like krlogin.

For the special case of editing files on the local host as another user, see the su or sudo methods. They offer shortened syntax for the `root' account, like /su::/etc/motd.

People who edit large files may want to consider scpc instead of ssh, or pscp instead of 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.

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5.5 Selecting a default user

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

     (setq tramp-default-user "root")

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

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

See the documentation for the variable tramp-default-user-alist for more details.

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

     Host here.somewhere.else
          User lily

than you must discard selecting a default user by tramp. This will be done by setting it to nil (or `lily', likewise):

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

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5.6 Selecting a default host

Finally, it is even possible to omit the host name part of a tramp file name. This case, the value of the variable tramp-default-host is used. Per default, it is initialized with the host name your local GNU Emacs is running.

If you, for example, use tramp mainly to contact the host `target' as user `john', you can specify:

     (setq tramp-default-user "john"
           tramp-default-host "target")

Then the simple file name `/ssh::' will connect you to John's home directory on target. Note, however, that the most simplification `/::' won't work, because `/:' is the prefix for quoted file names.

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5.7 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.

In order to specify such multiple hops, it is possible to define a proxy host to pass through, via the variable tramp-default-proxies-alist. This variable keeps a list of triples (host user proxy).

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

proxy must be a Tramp filename which localname part is ignored. Method and user name on proxy are optional, which is interpreted with the default values. The method must be an inline method (see Inline methods). If proxy is nil, no additional hop is required reaching user@host.

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

     (add-to-list 'tramp-default-proxies-alist
                  '("\\." nil "/ssh:bird@bastion.your.domain:"))
     (add-to-list 'tramp-default-proxies-alist
                  '("\\.your\\.domain\\'" nil nil))

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

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

     (add-to-list 'tramp-default-proxies-alist

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

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

     (add-to-list 'tramp-default-proxies-alist
                  '("\\.your\\.domain\\'" "\\`root\\'" "/ssh:%h:"))

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

This is the recommended configuration to work as `root' on remote Ubuntu hosts.

Next: , Previous: Multi-hops, Up: Configuration

5.8 Using Non-Standard Methods

There is a variable 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 C-h v tramp-methods <RET>.

Next: , Previous: Customizing Methods, Up: Configuration

5.9 Selecting config files for user/host name completion

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

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

— Function: tramp-get-completion-function method

This function returns the list of completion functions for method.


          (tramp-get-completion-function "rsh")
               => ((tramp-parse-rhosts "/etc/hosts.equiv")
                   (tramp-parse-rhosts "~/.rhosts"))
— Function: tramp-set-completion-function method function-list

This function sets function-list as list of completion functions for method.


          (tramp-set-completion-function "ssh"
           '((tramp-parse-sconfig "/etc/ssh_config")
             (tramp-parse-sconfig "~/.ssh/config")))
               => ((tramp-parse-sconfig "/etc/ssh_config")
                   (tramp-parse-sconfig "~/.ssh/config"))

The following predefined functions parsing configuration files exist:

This function parses files which are syntactical equivalent to ~/.rhosts. It returns both host names and user names, if specified.
This function parses files which are syntactical equivalent to ~/.ssh/known_hosts. Since there are no user names specified in such files, it can return host names only.
This function returns the host nicknames defined by Host entries in ~/.ssh/config style files.
SSH2 parsing of directories /etc/ssh2/hostkeys/* and ~/ssh2/hostkeys/*. Hosts are coded in file names User names are always nil.
Another SSH2 style parsing of directories like /etc/ssh2/knownhosts/* and ~/ssh2/knownhosts/*. This case, hosts names are coded in file names User names are always nil.
A function dedicated to /etc/hosts style files. It returns host names only.
A function which parses /etc/passwd like files. Obviously, it can return user names only.
Finally, a function which parses ~/.netrc like files.

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:

— Function: my-tramp-parse file

file must be either a file name on your host, or nil. The function must return a list of (user host), which are taken as candidates for user and host name completion.


          (my-tramp-parse "~/.my-tramp-hosts")
               => ((nil "toto") ("daniel" "melancholia"))

Next: , Previous: Customizing Completion, Up: Configuration

5.10 Reusing passwords for several connections.

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

By default, tramp caches the passwords entered by you. They will be reused next time if a connection needs them for the same user name and host name, independently of the connection method.

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

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 M-x tramp-clear-passwd in a buffer containing a related remote file or directory.

If you don't like this feature for security reasons, password caching can be disabled totally by customizing the variable password-cache (setting it to 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 load-path while loading tramp. If you don't use No Gnus, you can take password.el from the tramp contrib directory, see Installation parameters. It will be activated mandatory once No Gnus has found its way into GNU Emacs.

Next: , Previous: Password caching, Up: Configuration

5.11 Reusing connection related information.

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

tramp reads this file during startup, and writes it when exiting GNU Emacs. You can simply remove this file if tramp shall be urged to recompute these information next GNU Emacs startup time.

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

Next: , Previous: Connection caching, Up: Configuration

5.12 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 ls, test, find and cat.

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

Certain other tools, such as perl (or perl5) and 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 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. The symbol tramp-default-remote-path is a place holder, it is replaced by the list of directories received via the command getconf PATH on your remote machine. For example, on GNU Debian this is /bin:/usr/bin, whereas on Solaris this is /usr/xpg4/bin:/usr/ccs/bin:/usr/bin:/opt/SUNWspro/bin. It is recommended to apply this symbol on top of tramp-remote-path.

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

In this case, you can still use them with tramp. You simply need to add code to your .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:

     ;; We load tramp to define the variable.
     (require 'tramp)
     ;; We have perl in "/usr/local/perl/bin"
     (add-to-list 'tramp-remote-path "/usr/local/perl/bin")

Next: , Previous: Remote Programs, Up: Configuration

5.13 Remote shell setup hints

As explained in the 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 birth date 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 all situations. The other strategy is to require you to set up the remote host such that it behaves like tramp expects. 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 exists, and therefore it tries different possibilities. (On some hosts and shells, the command test -e does the trick, on some hosts the shell builtin doesn't work but the program /usr/bin/test -e or /bin/test -e works. And on still other hosts, 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.

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 shell-prompt-pattern has to be set correctly to recognize the shell prompt on the remote host.

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

This regular expression is used by tramp in the same way as 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 tramp is to log in to remote hosts as a different user. The default value of tramp-shell-prompt-pattern is the same as the default value of shell-prompt-pattern, which is reported to work well in many circumstances.
tset and other questions
Some people invoke the 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. 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 tramp. You can do this by checking the TERM environment variable, it will be set to dumb when connecting.

The variable tramp-terminal-type can be used to change this value to dumb.

The other approach is to teach tramp about these questions. See the variable tramp-actions-before-shell.

Environment variables named like users in .profile
If you have a user named frumple and set the variable FRUMPLE in your shell environment, then this might cause trouble. Maybe rename the variable to FRUMPLE_DIR or the like.

This weird effect was actually reported by a tramp user!

Non-Bourne commands in .profile
After logging in to the remote host, tramp issues the command exec /bin/sh. (Actually, the command is slightly different.) When /bin/sh is executed, it reads some init files, such as ~/.shrc or ~/.profile.

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

As an example, imagine somebody putting export FOO=bar into the 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 (~) character, say when adding ~/bin to $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 ~/.shrc and ~/.profile on all remote hosts is Bourne-compatible. In the above example, instead of export FOO=bar, you might use 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 ~/.bash_profile instead of ~/.profile, if the former exists. So bash aficionados just rename their ~/.profile to ~/.bash_profile on all remote hosts, and Bob's your uncle.

The 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 exec /bin/sh, 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 exec /bin/sh step. But how to find out if the shell is Bourne-ish?

Previous: Windows setup hints, Up: Configuration

5.14 Auto-save and Backup configuration

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

When backup-directory-alist is nil (the default), such problems do not occur.

Therefore, it is useful to set special values for tramp files. For example, the following statement effectively `turns off' the effect of backup-directory-alist for tramp files:

     (add-to-list 'backup-directory-alist
                  (cons tramp-file-name-regexp nil))

Another possibility is to use the tramp variable tramp-backup-directory-alist. This variable has the same meaning like backup-directory-alist. If a tramp file is backed up, and DIRECTORY is an absolute local file name, DIRECTORY is prepended with the tramp file name prefix of the file to be backed up.


     (add-to-list 'backup-directory-alist
                  (cons "." "~/.emacs.d/backups/"))
     (setq tramp-backup-directory-alist backup-directory-alist)

The backup file name of /su:root@localhost:/etc/secretfile would be /su:root@localhost:~/.emacs.d/backups/!su:root@localhost:!etc!secretfile~

The same problem can happen with auto-saving files. Since GNU Emacs 21, the variable auto-save-file-name-transforms keeps information, on which directory an auto-saved file should go. By default, it is initialized for tramp files to the local temporary directory.

On some versions of GNU Emacs, namely the version built for Debian GNU/Linux, the variable auto-save-file-name-transforms contains the directory where GNU Emacs 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, auto-save-file-name-transforms should be set to nil.

Another possibility is to set the variable tramp-auto-save-directory to a proper value.

Next: , Previous: Remote shell setup, Up: Configuration

5.15 Issues with Cygwin ssh

This section needs a lot of work! Please help.

The recent Cygwin installation of ssh works only with a Cygwinized GNU Emacs. You can check it by typing M-x eshell, and starting ssh test.machine. The problem is evident if you see a message like this:

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

Older ssh versions of Cygwin are told to cooperate with tramp selecting sshx as the connection method. You can find information about setting up Cygwin in their FAQ at

If you wish to use the scpx connection method, then you might have the problem that GNU Emacs calls scp with a Windows filename such as c:/foo. The Cygwin version of scp does not know about Windows filenames and interprets this as a remote filename on the host c.

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

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

If anyone knows how to start 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...

Next: , Previous: Configuration, Up: Top

6 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 Ange-FTP package.

Something that might happen which surprises you is that GNU Emacs remembers all your keystrokes, so if you see a password prompt from GNU Emacs, say, and hit <RET> twice instead of once, then the second keystroke will be processed by GNU Emacs after 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!

Next: , Up: Usage

6.1 tramp filename conventions

To access the file localname on the remote machine machine you would specify the filename /machine:localname. This will connect to machine and transfer the file using the default method. See Default Method.

Some examples of tramp filenames are shown below.

Edit the file .emacs in your home directory on the machine melancholia.
This edits the same file, using the fully qualified domain name of the machine.
This also edits the same file — the ~ is expanded to your home directory on the remote machine, just like it is locally.
This edits the file .emacs in the home directory of the user daniel on the machine melancholia. The ~<user> construct is expanded to the home directory of that user on the remote machine.
This edits the file /etc/squid.conf on the machine melancholia.

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 /user@machine:/path/to.file. That means that connecting to melancholia as daniel and editing .emacs in your home directory you would specify /daniel@melancholia:.emacs.

It is also possible to specify other file transfer methods (see Default Method) as part of the filename. This is done by putting the method before the user and host name, as in /method: (Note the trailing colon). The user, machine and file specification remain the same.

So, to connect to the machine melancholia as daniel, using the ssh method to transfer files, and edit .emacs in my home directory I would specify the filename /ssh:daniel@melancholia:.emacs.

Next: , Previous: Filename Syntax, Up: Usage

6.2 URL-like filename syntax

Additionally to the syntax described in the previous chapter, it is possible to use a URL-like syntax for tramp. This can be switched on by customizing the variable tramp-syntax. Please note that this feature is experimental for the time being.

The variable tramp-syntax must be set before requiring tramp:

     (setq tramp-syntax 'url)
     (require 'tramp)

Then, a tramp filename would look like this: /method://user@machine:port/path/to.file. /method:// is mandatory, all other parts are optional. :port is useful for methods only who support this.

The last example from the previous section would look like this: /ssh://daniel@melancholia/.emacs.

For the time being, tramp-syntax can have the following values:

Next: , Previous: Alternative Syntax, Up: Usage

6.3 Filename completion

Filename completion works with tramp for completion of method names, of user names and of machine names as well as for completion of file names on remote machines. In order to enable this, Partial Completion mode must be set on2.

If you, for example, type C-x C-f /t <TAB>, tramp might give you as result the choice for

     telnet:				   tmp/

`telnet:' is a possible completion for the respective method, `tmp/' stands for the directory /tmp on your local machine, and `toto:' might be a host tramp has detected in your ~/.ssh/known_hosts file (given you're using default method ssh).

If you go on to type e <TAB>, the minibuffer is completed to `/telnet:'. Next <TAB> brings you all machine names tramp detects in your /etc/hosts file, let's say

     telnet:		   telnet:

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

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

Remote machines, which have been visited in the past and kept persistently (see Connection caching), will be offered too.

Previous: Filename completion, Up: Usage

6.4 Integration with other GNU Emacs packages (experimental).

tramp has an experimental implementation for running processes on a remote host. This allows to exploit GNU Emacs packages without modification for remote file names. It does not work for the ftp and smb methods.

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

When your program is not found in the default search path tramp sets on the remote machine, you should either use an absolute path, or extend tramp-remote-path (see Remote Programs):

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

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

Adding an entry can be performed via add-to-list:

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

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

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

If you use other GNU Emacs packages which do not run out-of-the-box on a remote host, please let us know. We will try to integrate them as well. See Bug Reports.

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7 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. It is moderated so non-subscribers can post but messages will be delayed, possibly up to 48 hours (or longer in case of holidays), until the moderator approves your message.

The mailing list is at Messages sent to this address go to all the subscribers. This is not the address to send subscription requests to.

Subscribing to the list is performed via the tramp Mail Subscription Page.

To report a bug in tramp, you should execute 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. You should also check that your problem is not described already in See 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.

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

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

Sometimes, it might be even necessary to provide tramp function call traces. Such traces are enabled by the following code:

     (mapcar 'trace-function-background
             (mapcar 'intern
                     (all-completions "tramp-" obarray 'functionp)))

The function call traces are inserted in the buffer *trace-output*.

Next: , Previous: Bug Reports, Up: Top

8 Frequently Asked Questions

Next: , Previous: Concept Index, Up: Top

9 The inner workings of remote version control

Unlike 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 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.

Next: , Up: Version Control

9.1 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.

Next: , Previous: Version Controlled Files, Up: Version Control

9.2 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 call-process mechanism, a function that is somewhat more efficient than the shell-command function but that does not provide hooks for remote execution of commands.

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

In the case of a remote file, the 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.

Next: , Previous: Remote Commands, Up: Version Control

9.3 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 vc-workfile-unchanged-p function is advised to call an tramp specific function for remote files.

The 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.

Next: , Previous: Changed workfiles, Up: Version Control

9.4 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 vc-checkout knows about tramp files and allows version control to occur.

Previous: Checking out files, Up: Version Control

9.5 Things related to Version Control that don't fit elsewhere

Minor implementation details, &c.

Next: , Up: Miscellaneous Version Control

9.5.1 How VC determines who owns a workfile

GNU Emacs provides the user-login-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 NIS, NIS+ and 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 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 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.

Previous: Remote File Ownership, Up: Miscellaneous Version Control

9.5.2 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 rcs(1), cvs(1) or 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.

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10 How file names, directories and localnames are mangled and managed.

Up: Files directories and localnames

10.1 Breaking a localname into its components.

tramp file names are somewhat different, obviously, to ordinary file names. As such, the lisp functions file-name-directory and 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 localname and then rebuild the tramp file name with the result.

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

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11 How to Customize Traces

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

The verbosity levels are

 0 silent (no tramp messages at all)
 1 errors
 2 warnings
 3 connection to remote hosts (default verbosity)
 4 activities
 5 internal
 6 sent and received strings
 7 file caching
 8 connection properties
10 traces (huge)

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

The debug buffer is in Outline Mode. That means, you can change the level of messages to be viewed. If you want, for example, see only messages up to verbosity level 5, you must enter C-u 6 C-c C-q.

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

     (setq debug-on-error t
           debug-on-signal t)

Previous: Traces and Profiles, Up: Top

12 Debatable Issues and What Was Decided

Next: , Previous: Frequently Asked Questions, Up: Top

Concept Index

Table of Contents


[1] Invoking /bin/sh will fail if your login shell doesn't recognize `exec /bin/sh' as a valid command. Maybe you use the Scheme shell scsh...

[2] If you don't use Partial Completion mode, but want to keep full completion, load tramp like this in your .emacs:

     ;; Preserve Tramp's completion features.
     (let ((partial-completion-mode t))
       (require 'tramp))