Ubuntu – core file size with ulimit

bashcommand lineulimit

My question is probably not related to Ubuntu in particular, but since my desktop running this OS, I came to this forum.

I am trying to change the core file size using ulimit -c command as follows:

$ ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 7959
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
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) 1024
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

Changing the limitation:

$ ulimit -c unlimited

Observing the result:

$ ulimit -a
core file size          (blocks, -c) unlimited
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 7959
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
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) 1024
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

Indeed the limit is changed.
However, when I open another terminal and check the value, I still see zero value in core file size.

Questions:

Are changes made using ulimit command affect only current process, i.e. in this case the bash?
I launch a program from shell as a fore- or-background process. Does the ulimit change apply for new process ?
How can I make that all user processes are affected with this configuration ?

Best Answer

ulimit is a shell builtin, and thus only affects the current shell, and processes started by that shell:

$ type ulimit
ulimit is a shell builtin

From man ulimit:

The  ulimit  utility  shall  set  or report the file-size writing limit
imposed on files written by the shell and its child processes (files of
any  size  may be read). Only a process with appropriate privileges can
increase the limit.

So, yes, child processes are affected.

To set limits permanently or for all processes, edit /etc/security/limits.conf and reboot. The examples in the manpage are fairly good. You just need to add something like:

username - core unlimited

Related Solutions

Ubuntu – ulimit -u gives illegal option error when running from a script but not when from a terminal

ulimit is a shell builtin, not a program:

$ type ulimit
ulimit is a shell builtin

What it means is that ulimit may not work the same way with every shell.

The default shell in Ubuntu is Bash, and it is the shell you use from the terminal.

However in your script you are using sh, which (by default) is provided by is Dash, a shell similar, but different from Bash. Compare:

$ bash
$ ulimit -u
29901
$ dash
$ ulimit -u
dash: 1: ulimit: Illegal option -u

There are at least two solutions for your problem:

change your shebang from #!/bin/sh to #!/bin/bash;
use -p instead of -u.

I would recommend the first solution, because Bash has many more features than Dash. The drawback is that Bash is slower, but it your script is not performance-critical, this won't be a problem.

For more information about the difference between Bash's ulimit and Dash's ulimit, you can see man bash and man dash, then perform a search typing /ulimit. Additionally, Bash provides a help builtin that you can use as an alternative to the man page.

Ubuntu – How to remove limit on core dump file size

Per @Peter Bašista's answer in his own question:

At first, I thought this is an error and that's why I started this question. But it turned out it's simply a perfectly correct behavior. It turns out that RTFM saying applies here as well.

As man bash reveals, the ulimit built-in command has additional parameters: -H for setting the so-called hard limits and -S for setting the so-called soft limits. Moreover, if none of these options are given, the default behavior is that ulimit tries to set both the soft and the hard limits to the same value at once. And that was the problem.

Now there is a quote from the bash man page:

A hard limit cannot be increased by a non-root user once it is set;

So, there we go. The correct usage of ulimit command should always have this in mind. Most importantly, it should never be used without -H or -S options unless you are sure to know what you are doing (which at the time I obviously wasn't).

What I should have done is something like this:

After login: ulimit -H -c unlimited

Each time I want to change maximum core dump size limit ulimit -S -c <new size>

So, that's about it. I hope it could help someone who might struggle with a similar problem.

Best Answer

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Ubuntu – ulimit -u gives illegal option error when running from a script but not when from a terminal

Ubuntu – How to remove limit on core dump file size

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