4.6. Processes, signals and job control

Everytime a new application, shell or daemon is started, it gets a PID or process id. The list of running processes on a UNIX system can be obtained with the command ps. For example, to get the list of all running processes on the system, one can use ps -ax or ps -e.

Each of these running processes can be controlled with signals:

• To get the list of available signals on a system, see signal(3).
• To send a signal to a command from the shell, use the kill(1) command.

Processes running on the user's terminal can be controlled:

• to suspend the process temporaroly, use the sequence CTRL-Z
• to stop a running process, use the sequence CTRL-C
• processes in the running in background can be brought to the "foreground" with the command fg.
• a suspended process can be told to continue in the background with the command bg.

Several processes can be running in the background at the same time. They can be stopped or brought forward individually. To get the list of currently running jobs on the present terminal, use the jobs command.

Usually, when a shell is terminated, all the jobs (children) that were started by it and are still running are also terminated.