All,

I run a compute cluster with only a few users. Occasionally a user will accidently run a job on the master node that runs out RAM/swaps then hanges up for a while.

In /etc/security/limits.conf I have set memlock to 7.5GB (master has 8GB RAM) and maybe that is what lets the machine come back rather than hanging completely?

Is this the right setting to physocally limit a single user from asking for more RAM than the system has and bringing down the system? Should I set this to 2GB or so or is there something else I can do??

Any help much appreciated.

What OS? (Fedora?) What version?

If you don't want users chewing up more than 2GB RAM, then setting memlock to 7.5GB seems like a bad idea. Maybe you should post your limits.conf.

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Thanks for the reply

System is running 64-bit Fedora core 6. (Quite old now but I leave the OS alone until the hardware is replaced)

The 7.5 GB was there for another reason but I was asking whether it helped prevent total melt down of the system?

My secondary question was whether using the same method, but reducing the 7.5GB to say 2GB would prevent a user starting an application then reading in massive data files way beyong the memory on the system? (either not understanding what they are doing, or accidently starting a local job that was intented to run on many cluster nodes.

Here are my current entries in limits.conf

* soft memlock 7500000
* hard memlock 7500000

Thanks again

Greg.

Probably. Thing is: if there are enough processes eating up memory that are not affected by pam_limits(8) - i.e. daemons and other processes that don't have PAM support baked in or aren't configured correctly - you could still technically bring down your system. It sounds like your main concern is rogue/errant users, though.

Sure, assuming we're still talking about your system with 8GB RAM. 2GB would be a more sane restriction, IMO, depending on what the users are legitimately supposed to be doing. (As with all things: test this out to be sure pam_limits(8) is behaving the way you'd expect after making any changes.)

1 members found this post helpful.

Thanks again

My main concern was whether the memlock setting was doing what I thought from what you say it seems that it is. The setting of an appropriate value is the trick.

Too low could be overly restrictive of legitimate usage and too high still allows the system to lock up with accumulated other memory usage adding to the trouble maker process.

I think I might go with 4GB next time I can squeeze in a reboot and do some testing to check that it stops me using more than that.

Cheers,

Greg.