Check ulimit for non shell user

To check the ulimit of a running process if your unable to switch to the user.

Get the pid of the process and run the below.

 cat /proc/PIDHERE/limits

Issue starting mongodb

If you get the below error when starting mongodb

ERROR: child process failed, exited with error number 100

Try amending the mongod conf in /etc/mongo.conf by adding the below

smallfiles = true