command not found when using sudo ulimit

I was using ubuntu 12.04 ,on which I run ulimit -n ,it is showing 1024, I want to increase my open file limit from 1024 to 65535,so I tried the following command:

sudo ulimit -n 65535

but i get the following error:

sudo: ulimit: command not found

How to increase the file limit from 1024 to 65535? Any help will be appreciated.

ulimit is a shell builtin like cd, not a separate program. sudo looks for a binary to run, but there is no ulimit binary, which is why you get the error message. You need to run it in a shell.

However, while you do need to be root to raise the limit to 65535, you probably don’t want to run your program as root. So after you raise the limit you should switch back to the current user.

To do this, run:

sudo sh -c "ulimit -n 65535 && exec su $LOGNAME"

and you will get a new shell, without root privileges, but with the raised limit. The exec causes the new shell to replace the process with sudo privileges, so after you exit that shell, you won’t accidentally end up as root again.

I've had to deal with issues like this in the past. Since there is no setuid mechanism for shell scripts (because it's insecure), I've found writing a simple C wrapper with a setuid is suffice and then using a system call to modify the ulimits of the running process before dropping privileges and executing your shell script.