bash: ulimit: core file size: cannot modify limit: Operation not permitted
Solution 1:
Grep for a hard limit setting in your bash initialization files. From the bash man page.
A hard limit cannot be increased once it is set; a soft limit may be increased up to the value of the hard limit.
The hard limit is set via the ulimit -H flag. It may be set in /etc/bash* or /etc/profile* files. Look for a ulimit -Hc setting.
Solution 2:
I had this happen to me when I used dropbear as an SSH server. Apparently, dropbear sets some hard limits before spawning your shell.
Switching to OpenSSH solved the problem.