avoid killing SSH in out-of-memory

Question

When my server runs into out-of-memory, it usually kills several applications. How can i prevent from killing SSH? Because usually, when this out-of-memory error happens, my SSH is broken like this:

I connect to ssh server.
Enter username
Enter password

and then i wait

i wait

and wait...

and waaaaaaaaaait..

and then:

Connection timed out.

Is there any way to prevent this? How can i increase priority of process?

Answer 1

Run the following command as root. You probably want to add this into an init script somewhere.

echo -17 > /proc/`pidof sshd`/oom_adj

Update:

To ensure that the main daemon process is the one being adjusted, you can use this command. The above will probably fail if you have any SSH sessions open, so not such a great choice :(

echo -17 > /proc/`cat /var/run/sshd.pid`/oom_adj

-17 is the current value for OOM_DISABLE in /usr/include/linux/oom.h. You can read more about the Linux OOM killer here.