Automatically setting jobs (-j) flag for a multicore machine?

Question

I have a Makefile on a machine that has a ton of cores in it, but I always seem to forget to write -jX when compiling my project and it takes way longer than it

Answer 1

You can add a line to your Makefile similar to the following:

NUMJOBS=${NUMJOBS:-" -j4 "}

Then add a ${NUMJOBS} line in your rules, or add it into another Makefile var (like MAKEFLAGS). This will use the NUMJOBS envvar, if it exists; if it doesn't, automatically use -j4. You can tune or rename it to your taste.

(N.B.: Personally, I'd prefer the default to be -j1 or "", especially if it's going to be distributed to others, because although I have multiple cores also, I compile on many different platforms, and often forget to dis-able the -jX setting.)