Linux – ulimit -n not persisting, tried everything

Nevermind, it turns out the problem was a combination of ulimit -n and FD_SETSIZE. It seems like the application is using setrlimit to set ulimit -n to FD_SETSIZE. I fixed this by undefining and redifining __FD_SETSIZE to something larger.

So it seems MongoDB 1.6.5 doesn't work with the limit nofile line. You need to put ulimit -n X (where X is the file descriptors you want) just after the script keyword.

    script
        ulimit -n 60000
        PORT=27027
...

I guess the method using the pre-start block is for later versions of MongoDB.

Also for note, MongoDB has a hard limit of 20,000 connections, so it doesn't matter if you set file descriptors higher than that.

Another thing learned: starting and stopping using upstart scripts is not the same as REstarting. Starting and stopping threw errors on the limit nofile command, whereas restarting did not.