Locking shared memory

[Allen, Jack]

-----Original Message-----
From: Mike Kearey [mailto:mkearey at redhat.com] 
Sent: Wednesday, February 28, 2007 12:56 AM
To: General Red Hat Linux discussion list
Subject: Re: Locking shared memory

Allen, Jack wrote:

> I do not think the error is because of the first explanation of ENOMEM
> So my question is based on the second one. 
> 
> Is there a kernel or vm parameter that controls how much memory a
> process can utilize? 
> 
> I am running RH AS 4.4 32 bit with 2GB of physical memory. 
> 
> Thanks in advance: 
> Jack Allen 
> 

G'day Jack,

There is memlock limit in shell, changed using the ulimit command from
bash. See ulimit -l:

$ ulimit -l
32


The actual hard and soft limits are controlled on a Red Hat system using
the pam_limits pam module, using the config file
/etc/security/limits.conf

Check the doc's from RHEL4 for the pam module for details :

/usr/share/doc/pam-0.77/txts/README.pam_limits

This may well be where the ENOMEM came from, as the default limit that a
user may lock memory is 32kB.

Cheers,
Michael

=========================================
Michael:
	Thanks for the information. Since I do not want all users to
have the limit increased for them, I do not want to add and entry in
/etc/security/limits.conf. I know it can be done on a per user bases,
but any user can start the main database program that creates the shared
memory segments. And because the main program runs set UID and the owner
of the program is root, it runs as root no matter who starts. I know
there are those that think SUID programs to root are dangerous, but we
have to have it this way to make things work the way we want it to. It
is limited it what it does, in that it does not execute or create files,
etc.. arbitrarily, it has very specific things that is does.

	With that being said what I did was set the resource limit
within the program via setrlimit(RLIMIT_MEMLOCK,&rlimit). I set the
limit to 1GB and setrlimit returned a success value. But when I try to
lock the second 256MB shared memory segment address it still fails the
same way.

	The system has 2GB of memory and there is basically nothing else
running on the system other than all the standard/default processes for
various services.

	Do you or anyone else have anymore thoughts as to what may be
keeping me from locking the second shared memory segment address?

Thank:
Jack Allen