Working with Processes

Interacting with user-level and system-level processes is an important aspect of administering Linux. Table A.10 identifies many of the tools used for this purpose.

Table A.10. Commands for Working with Processes

COMMAND	GENERAL USAGE	DESCRIPTION
at	at TIME COMMAND	Executes a one-time command at the specified time.
bg	bg %JOB	Sends the specified job number to the background. Note: Pressing Ctrl+Z will suspend the current foreground process. After the process has been suspended, it can be moved to the background using bg. To start a process in the back- ground, append an ampersand (&) to the end of the command. For example: updatedb &
crontab	crontab [OPTIONS] USERNAME	Used to adjust or view a user's crontab. User crontabs contain commands scheduled for execution on a regular basis. Common options include -e Edit user's crontab -l List user's crontab
fg	fg %JOB	Brings the specified job number to the foreground.
jobs	jobs	Displays job numbers for all back- ground processes.
kill	kill [SIGNAL] PID	Sends a kill signal to the specified process. Common kill signals are
		SIGHUP (1)	Hang-up
		SIGINT (2)	Interrupt
		SIGTERM (15)	Terminate (default)
		SIGKILL (9)	Absolute kill
killall	killall [SIGNAL] PROCESS	Sends the specified kill signal to all processes using the designated process name.
nice	nice VALUE COMMAND	Executes the specified command using a manually designated nice value. Possible nice values range from -20 to +19. The lower the value, the higher the process priority.
nohup	nohup COMMAND	Executes the specified command in a no-hangup mode. This allows the process to continue execution after the initiating shell has been exited.
ps	ps [OPTIONS]	Displays information regarding running processes. Information displayed includes such things as the Process ID (PID), Parent Process ID (PPID), command line, and owner. Common options include -A All processes -f Full option listing
pstree	pstree	Displays running processes in a hierarchical formatincluding parent and child relationships.
renice	renice VALUE PID	Adjusts the nice value of a currently running process.
top	top	Displays statistical information regarding processes (memory allocation, priority, CPU utilization).