[tech] Process ulimits on Mussel and Martello

[David Adam]

So a certain genius who will remain nameless decided to see if a forkbomb 
would work on Mussel. Apparently this is no longer deserving of an account 
locking, but as it's not the first time in recent years I decided it was 
probably time we did something about it.

/etc/security/limits.conf on Mussel and Martello has been set with a soft 
limit of 4096 processes on all user accounts. getrlimit(2) informs me that 
on Linux this enforces a limit of 4096 threads per real UID. That's still 
enough to build Mozilla Firefox and run my screen session, and it's a soft 
limit anyway so if you're really struggling you can just bump it up with 
`ulimit -u onezillion` or whatever.

4096 was a number I pulled out of the air; there is little to no science 
behind it and is not intended to stand up to malicious attacks. There are 
still at least a thousand ways of exhausting resources on multiuser Linux 
systems anyway.

David Adam
UCC Wheel Member
zanchey at ucc.gu.uwa.edu.au