Cpu time limit

Each account is set up with a default limit for the maximum amount of processor time a task may use. If a task runs over the limit it is terminated with the message

Cputime limit exceeded

The purpose of the limit is to prevent background tasks which are left running after logout from inadvertently running "forever". Some tasks may legitimately require more cpu time than the default limit.

Ad Hoc CPU Limit Adjustments

A temporary limit change may be made by typing at the shell (%)

cpulimit 3600

Note that the "cpulimit" command is an alias defined either in your .cshrc file or in /public/cshrc.adjunct which is sourced by your .cshrc file. If you get "cpulimit: Command not found", you can add this alias to your .cshrc file and then re-login,

alias cpulimit 'setenv CPU \!*; limit cpu $CPU'

"cpulimit 3600" limits subsequent tasks, in the current session, making sure they do not individually exceed 3600 seconds of processor time.

The cpu limit can be turned off altogether (not a very good idea unless you are certain that you do not have a runaway job) by typing at the shell (%)

unlimit cpu

Changing the Default CPU Limit

You can change the default cpu limit for your account by adding a line like "cpulimit 3600" to the *end* of your .login and .cshrc files. [Actually only one or the other is necessary, but putting the command both places will save you the trouble of figuring out which one is appropriate for your system.]

Instructors or TAs can modify the cpu limit for all the students in a class. The technique depends on the system type and whether or not the course is set up using the OCE model. You may want to seek assistance from ACMS, but briefly, if the the course is using the OCE model, put the cpulimit command (e.g. "cpulimit 3600") in the prepfile for the course.

Avoiding Problems with CPU Limit when Editing

It is painful to have an editing session terminate due to the cputime limit, particularly if you are in visual mode. The terminal is left in a strange state where characters are not echoed, and the LINEFEED key must be used instead of RETURN. If you ever "bomb" out of visual, try (blindly) typing

LINEFEED reset LINEFEED.

To avoid the possibility of running out of cpu time while editing, most accounts have an alias specified for vi which temporarily unlimits cpu time during visual editing sessions. See /public/cshrc for an example of such an alias.

For more information regarding the command "limit" see "man csh".