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I am compiling some programs here and I have 4 cores. Is there a way to tell make, cmake or gcc to compile using all cores or something to that affect.

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1 Answer 1

up vote 10 down vote accepted

If a package supports it you can use the -j flag to allow parallel jobs running, e.g.:

make -j8

More details on this flag can be found in the Stackoverflow question Why does make -j perform better when it is passed a number larger than the number of cores available?.

Distributed compilation

If you have multiple machines, give distcc a go. On the involved machines, sudo apt-get install distcc. Assuming that your build machine is 192.168.1.1:

  • on the helper machines, run:

    sudo distccd --log-file=/tmp/distccd.log --daemon -a 192.168.1.1
    
  • On the build machine, before running configure or cmake you have to specify hosts that you want to use for the build process. Optionally, specify the number of simultaneous jobs after a slash (defaulting to 4):

    export DISTCC_HOSTS='localhost/4 192.168.1.2/8 192.168.1.3/8'
    

    Make the compiler use distcc:

    export PATH="/usr/lib/distcc:$PATH"
    

    Now configure or cmake the application and build with:

    make -j$(distcc -j)
    

    Note that if you've put /usr/lib/distcc twice in your PATH, it'll fail. Be sure to set /usr/lib/distcc only once in your PATH.

For more details, see the manual pages for distcc(1) and distccd(1).

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OMG that J is good. I went from 15 minutes to less than 1. thanks L. –  Luis Alvarado Feb 23 '12 at 17:22
    
It can get faster with distcc, compilation of PHP was done in 2 minutes, the kernel was done in 3 minutes (three i5 machines) –  Lekensteyn Feb 23 '12 at 17:24
    
Will try with distcc when i get to work. Was asking a similar question about this yesterday. Maybe you can help with it here: askubuntu.com/questions/106810/… –  Luis Alvarado Feb 23 '12 at 17:39
    
Running distccd as root seems like a bad plan. I've not used it for a few reasons but when I did I can't have used root because I didn't have permission on those machines. –  ams Feb 24 '12 at 9:23
    
@ams You do not need to run it as root. If you run it as root and want to switch users, use distccd --user nobody. Otherwise, it'll run under the user who executed it. –  Lekensteyn Feb 24 '12 at 9:57

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