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When writing program, there are times when a runaway program slurps half of my RAM (generally due to practically infinite loops while creating large data structures), and bringing the system to become really slow that I can't even kill the offending program. So I want to use ulimit to automatically kill my program automatically when my program is using an abnormal amount of memory:

$ ulimit -a
core file size          (blocks, -c) 1000
data seg size           (kbytes, -d) 10000
scheduling priority             (-e) 0
file size               (blocks, -f) 1000
pending signals                 (-i) 6985
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) 10000
open files                      (-n) 1024
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 6985
virtual memory          (kbytes, -v) 100000
file locks                      (-x) unlimited
$ ./run_program

but why is my program still using more RAM than the given limit (yes, I'm starting the program in the same bash shell)?

Have I misunderstood something about ulimit?

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As you can see, there are limits on several different kinds of memory. Figuring out towards which limits a particular allocation count is sometimes tricky. Try to get a “runaway” process and post the contents of /proc/12345/status where 12345 is the process ID (just the lines beginning with Vm are enough). –  Gilles Nov 2 '10 at 23:43
    
@Gilles: I've tried putting additional constrains on "max memory size", "virtual memory", "core file size", "data seg size", basically everything I can see in ulimit that is related to memory (I don't use much files). The problem with collecting from /proc/ is that my computer locks up in 2-3 seconds after the runaway started, and I have to struggle really hard to be able to kill the offending process (many times, I'd just use the power button). I'll try acquire one though. –  Lie Ryan Nov 3 '10 at 1:28

2 Answers 2

up vote 2 down vote accepted

Your example should work like you think (program gets killed after consuming too much RAM). I just did a small test on my shell server:

First I restricted my limits to be REALLY low:

ulimit -m 10
ulimit -v 10

That lead to about everything getting killed. ls, date and other small commands will be shot before they even begin.

What Linux distribution you use? Does your program use only a single process or does it spawn tons of child processes? In the latter case ulimit might not always be effective.

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I'm using gentoo and my program didn't spawn any subprocesses, but it uses SDL and OpenGL, could that be the cause? Setting ulimit to an extremely low value do cause ls, etc and my program to get killed. The program requires between 4000-8000 on normal use (at 4000 the SDL library doesn't get loaded, and at 8000 the program doesn't get killed even though top showed that it ate more than half a gigabytes of RAM) –  Lie Ryan Nov 2 '10 at 14:53

This only works in a single bash session unless you put it into your .bash_profile and won't apply for the already running processes.

What I find strange is that the:

 max memory size         (kbytes, -m) unlimited

is not present in /etc/security/limits.conf even tho it's only limits memory consumption per process not overall for 1 user account. Instead of them adding Cgroup, they should have just modify the existing unix commands to accomodate those new features.

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I knew that ulimit only work within the same bash shell for programs started after the limit is set (see how I started the program from my sample shell session), my question was that the limit still didn't work even after taking that into account. –  Lie Ryan Aug 22 at 11:10

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