User accounts in Cpanel servers with jailshell enabled seems to get this error sometimes (When trying to run some commands in console):

-jailshell: fork: Resource temporarily unavailable

I believe this is a bug in Cpanel's jailshell. It may let you use some commands, but usually any command (ls, cat etc.) returns this error. This can be corrected easily:

1) Login to WHM
2) Suspend the account with this issue
3) Unsuspend the account with this issue
4) Done. Suspend/Unsuspend seems to reset the jailshell for the account and remove the error.