How to limit a process to one CPU core in Linux?

Under Linux, execute the sched_setaffinity system call. The affinity of a process is the set of processors on which it can run. There's a standard shell wrapper: taskset. For example, to pin a process to CPU #0 (you need to choose a specific CPU):

taskset -c 0 mycommand --option  # start a command with the given affinity
taskset -c -pa 0 1234            # set the affinity of a running process

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There are third-party modules for both Perl (Sys::CpuAffinity) and Python (affinity) to set a process's affinity. Both of these work on both Linux and Windows (Windows may require other third-party modules with Sys::CpuAffinity); Sys::CpuAffinity also works on several other unix variants.

If you want to set a process's affinity from the time of its birth, set the current process's affinity immediately before calling execve. Here's a trivial wrapper that forces a process to execute on CPU 0.

#!/usr/bin/env perl
use POSIX;
use Sys::CPUAffinity;
Sys::CpuAffinity::setAffinity(getpid(), [0]);
exec $ARGV[0] @ARGV

You can build cpu-sets on the command line as well. man cpuset Later on you can assign (running) processes to these.