Hide

What's this?

commandlinefu.com is the place to record those command-line gems that you return to again and again.

Delete that bloated snippets file you've been using and share your personal repository with the world. That way others can gain from your CLI wisdom and you from theirs too. All commands can be commented on, discussed and voted up or down.


If you have a new feature suggestion or find a bug, please get in touch via http://commandlinefu.uservoice.com/

Get involved!

You can sign-in using OpenID credentials, or register a traditional username and password.

First-time OpenID users will be automatically assigned a username which can be changed after signing in.

Hide

Stay in the loop…

Follow the Tweets.

Every new command is wrapped in a tweet and posted to Twitter. Following the stream is a great way of staying abreast of the latest commands. For the more discerning, there are Twitter accounts for commands that get a minimum of 3 and 10 votes - that way only the great commands get tweeted.

» http://twitter.com/commandlinefu
» http://twitter.com/commandlinefu3
» http://twitter.com/commandlinefu10

Subscribe to the feeds.

Use your favourite RSS aggregator to stay in touch with the latest commands. There are feeds mirroring the 3 Twitter streams as well as for virtually every other subset (users, tags, functions,…):

Subscribe to the feed for:

Hide

News

2011-03-12 - Confoo 2011 presentation
Slides are available from the commandlinefu presentation at Confoo 2011: http://presentations.codeinthehole.com/confoo2011/
2011-01-04 - Moderation now required for new commands
To try and put and end to the spamming, new commands require moderation before they will appear on the site.
2010-12-27 - Apologies for not banning the trolls sooner
Have been away from the interwebs over Christmas. Will be more vigilant henceforth.
2010-09-24 - OAuth and pagination problems fixed
Apologies for the delay in getting Twitter's OAuth supported. Annoying pagination gremlin also fixed.
Hide

Tags

Hide

Functions

Use all the cores or CPUs when compiling

Terminal - Use all the cores or CPUs when compiling
make -j 4
2009-08-05 22:50:57
User: kovan
Functions: make
16
Use all the cores or CPUs when compiling

Force make command to create as many compile processes as specified (4 in the example), so that each one goes into one core or CPU and compilation happens in parallel. This reduces the time required to compile a program by up to a half in the case of CPUs with 2 cores, one fourth in the case of quad cores... and so on.

Alternatives

There are 4 alternatives - vote for the best!

Terminal - Alternatives

Know a better way?

If you can do better, submit your command here.

What others think

Is there an easy way to know how many CPUs you have?

Then the command could be:

make -j $(cat /proc/cpus)
Comment by matthewbauer 273 weeks and 2 days ago

Your compilation only experience a n-fold linear speedup (with n being the number of CPU/cores) if your code has only parallel components and no serial components (dependencies in your code).

In the case of even a slight amount of serial components (i.e. 1-2%), speedup is greatly affected. This is the essence of Amdahl's Law.

Comment by DeusExMachina 273 weeks and 2 days ago

@mattthewbauer in Linux you could do somethink like make -j $(grep -c ^processor /proc/cpuinfo). It doesn't do any bad to use a higher number than the actual number of cores thought.

@DeusExMachina: true but usually the speed increase is linear or nearly linear, because AFAIK in Makefiles interdependencies only exist between targets, so all the source files of each target can be compiled in parallel.

Comment by kovan 273 weeks and 1 day ago

From my make manpage, "If the -j option is given without an argument, make will not limit the number of jobs that can run simultaneously." That suggests this command shouldn't help at all. Am I wrong?

Comment by tremby 270 weeks and 4 days ago

Oh, facepalm. I read it (more than once) as "If the -j option is not given". Never mind.

Comment by tremby 270 weeks and 4 days ago

Your point of view

You must be signed in to comment.

Related sites and podcasts