Linux – Running a process with both low cpu and I/O priority on rhel4

You can tune the OOM killer, to prefer certain processes. Each process has a score that indicates the likelihood of the process being killed in case the system runs in OOM situation. You can see the score of a process in /proc/${PID}/oom_score. You can bias the decision of the OOM killer using /proc/${PID}/oom_adj: a high value increases the probability that OOM killer is going to kill ${PID}. The value of oom_adj is inherited by children so you just set it in the master apache process at startup (in this case you should hava a watchdog that restarts apache); an alternative is to leave the master process at its default level and tune up each child so that the master stays alive and re-spawns the children as needed (in this case you need an external daemon that checks for new children and tunes oom_adj). Of course this assumes that you are using the multi process worker ;-)

Please note that the normal range of oom_adj values (-16,15) is only a bias, the heuristic of the OOM killer may still choose another process if its score is high enough. The special value -17 makes the process unkillable by OOM killer, but it's dangerous, because if the unkillable process (e.g. you DB) goes berserk the kernel may be unable to recover from the memory shortage.

Have a look at reptyr, which does exactly that. The github page has all the information.

reptyr - A tool for "re-ptying" programs.

reptyr is a utility for taking an existing running program and attaching it to a new terminal. Started a long-running process over ssh, but have to leave and don't want to interrupt it? Just start a screen, use reptyr to grab it, and then kill the ssh session and head on home.

USAGE

reptyr PID

"reptyr PID" will grab the process with id PID and attach it to your current terminal.

After attaching, the process will take input from and write output to the new terminal, including ^C and ^Z. (Unfortunately, if you background it, you will still have to run "bg" or "fg" in the old terminal. This is likely impossible to fix in a reasonable way without patching your shell.)