Terminating Processes

Terminating Processes

From time to time a process may use so much memory, disk, or CPU time that your only alternative is to terminate it before it causes a system crash. Before you kill a process, make sure that the user who invoked the process will not try to invoke it again. You should, if at all possible, speak to the user before killing the process, and at a minimum you should notify the user that the process was prematurely terminated and give a reason for the termination. If you do this, the user can reinvoke the process at a lower priority or possibly use the system's job processing facilities (at, batch, and cron) to execute the process at another time.

To terminate a process, you use the kill command. Typically, for most terminations, you should use the kill -15 variation. The -15 flag indicates that the process is to be allowed time to exit gracefully, closing any open files and descriptors. The -9 flag to kill terminates the process immediately, with no provision for cleanup. If the process you are going to kill has any child processes executing, using the kill -9 command may cause those child processes to continue to exist on the process table, though they will not be responsive to input. The wait(1) command, given with the process number of the child process, removes them. For complete information about the syntax and usage of the kill command, see the kill(1) reference page. You must always know the PID of the process you intend to kill with the kill command.

Killing Processes by Name with the killall(1M) Command

The killall(1M) command allows you to kill processes by their command name. For example, if you wish to kill the program a.out that you invoked, use the syntax:

killall a.out

This command allows you to kill processes without the time-consuming task of looking up the process ID number with the ps(1M) command.

Note: This command kills all instances of the named program running under your shell and if invoked with no arguments, kills all processes on the system that are killable by the user who invoked the command. For ordinary users, these are simply the processes invoked and forked by that user, but if invoked by root, all processes on the system will be killed. For this reason, this command should be used carefully.

Chapter 8 describes the cadmin object system and the tasks used to administer this set of daemons and tools. Topics described in this chapter include:

A description of the cadmin object system
Starting and stopping the cadmin daemons
Troubleshooting the cadmin object system

Chapter 8