GNU Parallel


GNU parallel is a shell tool for executing jobs in parallel using one or more computers. A job can be a single command or a small script that has to be run for each of the lines in the input. The typical input is a list of files, a list of hosts, a list of users, a list of URLs, or a list of tables. A job can also be a command that reads from a pipe. GNU parallel can then split the input and pipe it into commands in parallel.

GNU Parallel

For people who live life in the parallel lane

If you use xargs and tee today you will find GNU parallel very easy to use as GNU parallel is written to have the same options as xargs. If you write loops in shell, you will find GNU parallel may be able to replace most of the loops and make them run faster by running several jobs in parallel.

GNU parallel makes sure output from the commands is the same output as you would get had you run the commands sequentially. This makes it possible to use output from GNU parallel as input for other programs.

For each line of input GNU parallel will execute command with the line as arguments. If no command is given, the line of input is executed. Several lines will be run in parallel. GNU parallel can often be used as a substitute for xargs or cat | bash.

Download

Stable source releases:

They are available on the main GNU server (HTTPSHTTPFTP) and its mirrors; please use a mirror if possible.

Latest release

Official packages, for:
Community maintained packages:
  • untested .deb/.rpm packages for Debian, CentOS, Arch, Fedora, Mandriva, RedHat, OpenSUSE, and xUbuntu at build.opensuse.org,
  • packages for Solaris at Sun OpenCSW,
  • .rpm packages for AIX at Perzl.org.

Documentation

A lot of work has been put into making documentation for GNU parallel. GNU parallel includes the 4 types of documentation: Tutorial, How-To, Reference and Design Discussion.

Tutorial

If you prefer reading a book buy GNU Parallel 2018 at https://www.lulu.com/shop/ole-tange/gnu-parallel-2018/paperback/product-23558902.html or download it at: https://doi.org/10.5281/zenodo.1146014 (source) Read at least chapter 1+2. It should take you less than 20 minutes.

Otherwise start by watching the intro videos for a quick introduction: http://www.youtube.com/playlist?list=PL284C9FF2488BC6D1

If you want to dive deeper: spend a couple of hours walking through the tutorial (man parallel_tutorial, HTML, PDF). Your command line will love you for it.

How-To

You can find a lot of EXAMPLEs of use after the list of OPTIONS in man parallel (Use LESS=+/EXAMPLE: man parallel) (HTML, PDF). That will give you an idea of what GNU parallel is capable of, and you may find a solution you can simply adapt to your situation.

Reference

If you need a one page printable cheat sheet you can find it on: https://www.gnu.org/software/parallel/parallel_cheat.pdf

parallel --help shows you the most commonly used options.

The man page is the reference for all options (man parallel, HTML, PDF). The options map is a map showing which options other options relate to (/usr/share/.../parallel_options_map.pdf, PDF).

There are separate man pages for:

  • env_parallel (man env_parallel, HTML, PDF),
  • sem (man sem, HTML, PDF),
  • parcat (man parcat, HTML, PDF),
  • parset (man parset, HTML, PDF),
  • parsort (man parsort, HTML, PDF),
  • GNU sql (man sql, HTML, PDF), and
  • GNU niceload (man niceload, HTML, PDF).

For alternatives to GNU parallel, see man parallel_alternatives (HTML, PDF).

Design discussion

If you want to know the design decisions behind GNU parallel, see: man parallel_design (HTML, PDF). This is also a good intro if you intend to change GNU parallel.

You may also want to learn about the history of GNU parallel.

Over the years GNU parallel has gotten more safety features (e.g. no silent data loss if the disk runs full in the middle of a job). These features cost performance. This graph shows the relative performance between each version.

Citation

When using GNU parallel for a publication please cite as per parallel --citation. Read the background for the citation in The GNU Parallel Citation FAQ.

10 year anniversary and 20th birthday

On 2020-04-22 GNU parallel has been an official GNU tool for 10 years. Read more about the anniversary.

GNU parallel's 20th birthday is on 2022-01-06. Read more about the birthday.

Mailing lists

GNU parallel has two mailing lists:

  • <parallel@gnu.org> for discussing uses of GNU parallel. Subscribe on the web interface.
  • <bug-parallel@gnu.org> (web interface) for discussing development and enhancement requests, as well as bug reports.

    Your bug report should always include:

    • The output of parallel --version. If you are not running the latest released version, you should specify why you believe the problem is not fixed in that version.
    • A complete example that others can run, which shows the problem. A combination of seq, cat, echo, and sleep can reproduce most errors. If your example requires large files, see if you can make them with something like seq 1000000 > file.

Announcements about GNU parallel and most other GNU software are made on <info-gnu@gnu.org> (web interface).

Getting involved

Development of GNU parallel, and GNU in general, is a volunteer effort, and you can contribute. For information, please read How to help GNU. If you'd like to get involved, it's a good idea to join the discussion mailing list (see above).

Test releases
Trying the latest test release (when available) is always appreciated. Test releases of GNU parallel can be found on the GNU "alpha" server  (HTTPSHTTPFTP) and its mirrors.
Development
For development sources, bug and patch trackers, and other information, please see the GNU parallel project page at savannah.gnu.org.
Maintainer
GNU parallel is currently maintained by Ole Tange. Please use the mailing lists for contact.

Merchandise

You can show your support for GNU parallel using our merchandise.

Licensing

GNU parallel 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 3 of the License, or (at your option) any later version.

When using GNU parallel for a publication please cite:

O. Tange (2018): GNU Parallel 2018, March 2018, https://doi.org/10.5281/zenodo.1146014.