Shared memory controls in Solaris 10

The new facilities in Solaris 10 makes such settings dynamic, but the controls to prevent overallocation are still there, albeit in a slightly modified form.

There are two approaches these days..

1. /etc/system (yawn, requires a reboot - why would you?)
2. Projects

The IPC settings are entirely controlled by projects these days.. the ability to set values in /etc/system is there solely for backwards compatibility, and simply sets the default values for the projects, and therefore should be considered deprecated.

Probably the best way to explain the use of projects to set default values is to run through a quick worked example of setting the shared memory max allocation (shmmax), with comments inline:

$ uname -a

SunOS deepthought 5.11 snv_69 i86pc i386 i86pc

$ id -a

uid=500(mike) gid=100(users) groups=100(users)

The user we're running as has no specific privs, such as would be the case with an Oracle application account (for example). There is no settings in /etc/system, so we're running with default values.

As an aside, this is running under VMware server on a Linux host with 256MB memory allocated to the VM. The default value of shmmax is calculated as physmem/4, so we ought to see maximum allocation around about 64MB

We can check what the max shm is going to be using Solaris 10 prctl command:

$ prctl -n project.max-shm-memory $$

process: 6905: ksh -o vi

NAME    PRIVILEGE       VALUE    FLAG   ACTION                       RECIPIENT

project.max-shm-memory

         privileged      61.9MB      -   deny                                 -

         system          16.0EB    max   deny                                 -

$

That's reporting 61.9MB, which is pretty close to the expected 64MB. I wonder where the other 3.1MB went?

And to prove the point, I've just written a wee program that tests this, by creating (and destroying) increasingly large segments of shared memory (incrememnting by 1MB at each iteration). It stops when it fails and reports the last created seg.

$ ./findmax

Shared seg created with 61.0 MB

shmget failed!

$

So, here's how we increase it.. We need root privs, or a friendly sysadmin for this, as we're adding a new project for this user only:

$ su

Password:

# projadd -U mike -K "project.max-shm-memory=(priv,80MB,deny)" user.mike

#

Back on as me now.. (notice I'm logging on again by su'ing back to myself, rather than just exiting the "su" shell - this is deliberate)

# su - mike

Sun Microsystems Inc.   SunOS 5.11      snv_69  October 2007

$ prctl -n project.max-shm-memory $$

process: 7044: ksh

NAME    PRIVILEGE       VALUE    FLAG   ACTION                       RECIPIENT

project.max-shm-memory

         privileged      80.0MB      -   deny                                 -

         system          16.0EB    max   deny                                 -

$

$ ./findmax

Shared seg created with 80.0 MB

shmget failed!

$