topic Re: current limits of a process in Operating System - Linux

current limits of a process

Jdamian — Thu, 18 Nov 2010 08:57:46 GMT

Hi

The configuration file /etc/security/limits.conf contains the limits per user.

Once a process is created (for instance, PID 333) its limits can be displayed using
cat /proc/333/limits
BUT only in some of my nodes... not in others

How can I select/unselect that feature?
Does it depend on kernel version or on a specific kernel module?

Thanx in advance

Re: current limits of a process

Matti_Kurkela — Thu, 18 Nov 2010 09:33:05 GMT

The virtual file /proc//limits does exist in RHEL 4 and later, but not in RHEL 3. It might be a feature of the Linux 2.6.xx kernel series.

...Yes, seems like it: it does not exist in even the latest 2.4.xx kernel.

It is defined in /fs/proc/base.c, so it's part of the base feature set of the /proc filesystem. It cannot be disabled without changing the kernel source code or disabling the entire /proc filesystem.

But because only the owner of the process (or root, of course) can view the limits, I don't see how this feature could cause any harm.

The owner of each /proc//limits file is equal to the owner of the respective process, and the permissions of the file are 400 (-r--------).

MK

Re: current limits of a process

Jdamian — Thu, 18 Nov 2010 10:54:46 GMT

I agree that kernels before 2.6 hadn't this feature but all my nodes are 2.6 and some of them have it and other haven't.

For instance:
# uname -a
Linux mynode 2.6.18-8.el5 #1 SMP Fri Jan 26 14:15:21 EST 2007 i686 i686 i386 GNU/Linux

# cat /etc/redhat-release
Red Hat Enterprise Linux Server release 5 (Tikanga)

# cat /proc/$$/limits
cat: /proc/13905/limits: No such file or directory

Re: current limits of a process

Goran Koruga — Thu, 18 Nov 2010 11:24:23 GMT

Hello.

'man 5 proc' says:

/proc/[number]/limits (since kernel 2.6.24)

Does this help?

Regards,
Goran

Re: current limits of a process

Matti_Kurkela — Thu, 18 Nov 2010 11:31:00 GMT

Interesting... apparently it's something RedHat has backported to both RHEL 4 and RHEL 5 kernels in later kernel RPMs.

This is a RHEL 4 system. Notice it has been updated since the initial release of RHEL 4:

$ cat /etc/redhat-release
Red Hat Enterprise Linux ES release 4 (Nahant Update 7)
$ uname -a
Linux myhost 2.6.9-78.0.17.ELsmp #1 SMP Thu Mar 5 04:58:34 EST 2009 x86_64 x86_64 x86_64 GNU/Linux
$ cat /proc/$$/limits
Limit Soft Limit Hard Limit Units
Max cpu time unlimited unlimited seconds
Max file size unlimited unlimited bytes
Max data size unlimited unlimited bytes
[...]

According to kernel.org Gitweb, the /proc//limits feature was committed to Linus's main kernel source tree on 2007-10-19. I guess RedHat has backported it and included it to their RHEL 4 and RHEL 5 kernel updates at some date after that.

...Yes, looking at RHEL release notes, this feature was added in RHEL 5.2 and in RHEL 4.7.

(Wikipedia's RHEL page includes the release dates of each update release and links to the release notes, so it's easy to check the appropriate sets of release notes.)

MK

Re: current limits of a process

Jdamian — Fri, 19 Nov 2010 07:03:42 GMT

thanx everyone