sshlatex: A collection of hacks to efficiently run LaTeX via ssh

Tired of long LaTeX compile times on your old, slow computer? Do you want a tool which monitors your source file for changes, copies it to a fast remote server, runs LaTeX there, and downloads the resulting PDF file?

Then look no further. Actually, you should; this repository is a collection of horrible hacks to make this possible. They work for me. Highlights are that sshlatex prestarts LaTeX on the server with the previous run's preamble to preload all those required LaTeX packages and that it starts streaming the PDF file before LaTeX finishes creating it.

Usage

1. Run sshlatex ssh.example.org foo.tex in the background. Just as with pdflatex, you may drop the extension .tex if you want to.
2. Work on your file foo.tex.
3. Enjoy an updated PDF each time you save your changes.

Optionally, put a program beepy in your $PATH (or change the corresponding line in the source code) to audibly inform you of a completed run. Useful for when you're switching virtual desktops and don't see the output of sshlatex.

• See below for when you don't have passphrase-less login to the remote end set up.

• Tip for when you're using a lightweight PDF viewer which doesn't auto-reload on changes: Put something like the following in your beepy program.

  # Send the "r" key to all running mupdf instances.
  for i in `xdotool search --class mupdf`; do
      xdotool key --window $i r
  done

• Use the draft option in your LaTeX \documentclass command to further speed up compilation. For instance, this option disables the microtype package.

Features

• No installation is necessary, neither on the remote host nor on the local side.

• Images, sources, bibliography lists, and local class and style files (for instance embedded using \includegraphics, \input, or \include) are automatically copied to the compile server. Using a crude heuristic, this even extends to files included by custom commands.

• Even before the source file is changed, LaTeX gets already started on the remote host with the preamble of the previous run. This way all the required packages are already loaded when the new version is ready to be compiled, shaving off a couple of hundreds of milliseconds.

  If you want more parts of your document to be precompiled, not only the preamble, then put a commented % \begin{document} declaration between the part which should be precompiled and the part which changes often. LaTeX will ignore this declaration, but sshlatex will use it to determine where to split the file.

• Downloading the resulting PDF file starts before each run of pdflatex has finished. Since pdflatex does not simply append to the output file, but seeks and overwrites earlier parts, sshlatex is prepared to transfer some blocks multiple times if necessary. This is still faster than waiting for pdflatex to finish and then doing a proper rsync.

• Temporary files on the server are properly cleaned up on ^C.

• Filenames with special characters in them are supported.

• Proper care is taken to ensure that shell commands directed at the remote host are interpreted by the bash, even if a different shell is the default.

Dependencies

Aside from standard Linux tools and Perl 5 (included in the base installation of practically any Linux distribution), sshlatex has no dependencies on the local host and only LaTeX on the remote host. If inotifywait from the inotify-tools package is installed on the local side, sshlatex will use it instead of resorting to polling for detecting changes in the source files.

You should use the multiplexing capabilities of ssh, so that new connections are piggybacked over an already established connection avoiding the time-consuming TCP and cryptography handshake. Add the following two lines to your local ~/.ssh/config and open a separate SSH connection before you start sshlatex.

ControlMaster auto
ControlPath ~/.ssh/control:%h:%p:%r

If you don't have passphrase-less login to the remote end set up, ssh multiplexing is not only nice to have, but absolutely crucial, as else you'd be forced to enter login credentials each time you change the LaTeX source.

Purely local usage

Because of the prestart feature, sshlatex can even make sense if you run it purely locally. Call sshlatex localhost foo.tex. Invoked with the special hostname localhost, sshlatex avoids actually calling ssh. Therefore this command will work even if you don't have an ssh server running on localhost.

Security considerations

Essentially, don't run sshlatex on untrusted files or with untrusted servers. Specifically:

• sshlatex places several files, including LaTeX source files, in a temporary directory on the server side. This might leak data or metadata (for instance on when you are working on your LaTeX documents) to the administrator or other users on the server. You can change the location of the temporary directory by arranging an appropriate value of $TMPDIR on the remote end.
• sshlatex happily uploads any included files to the server, even files outside the base directory (as for instance prompted by a command like \includegraphics{/etc/passwd} in the LaTeX source file).
• When downloading the resulting PDF file, sshlatex accepts any data from the server. This could be exploited by an attacker for a denial of service attack by filling the memory or disk.
• The usual problems with compiling untrusted LaTeX source files apply.

Shortcomings

• Written in haste, will contain bugs. Is a grave assortment of hacks, the least of which is using the LC_* environment variables to pass data to the remote host.
• Not customizable.
• Doesn't support fancy reruns of LaTeX for making sure that references are correct and so on. This tool is for rapidly iterating.

License

sshlatex is dual-licensed, meaning that you can (and are invited to) use, redistribute and modify it under the terms of either:

1. The GNU General Public License (GPL), version 3 or (at your option) any later version published by the Free Software Foundation.
2. The LaTeX Project Public License (LPPL), version 1.3c or (at your option) any later version published by the LaTeX3 project.