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kill

summary

    This subchapter looks at kill, a Unix (and Linux) command.

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kill

    This subchapter looks at kill, a Unix (and Linux) command.

    kill is used to send signals to a process, most often to stop processes.

    kill is a builtin command in csh. There is also an external utility with the same name and functionality.

which processes can be killed

    An ordinary user can only kill his or her own processes.

    A system administrator running as root (including using sudo) can use kill on any process on the entire system.

frozen process

    Sometimes a process (particularly web browsers) will freeze up. The kill command can be used to remove the frozen program from the system.

    If a user finds their display locked up because of a frozen program, he or she can login to another computer, then login to the original system using rlogin, and then use the kill command to stop the offending process using the specific process ID.

killall

    killall is a related command. killall program_name will stop all processes with the program name, so the more specific kill with a specific process ID is usually used first.

process isolation

    Unix does a very good job of keeping processes isolated from each other, so that no rogue process can attack or damage any other process.

    Unlike Windows, a frozen or crashed program on UNIX or Linux shouldn’t be able to bring the entire operating system to a halt.

    Most Unix vendors carefully test their own system software and most of the system software has been running and tested for decades, so those programs rarely cause problems.

    Most bugs occur in third party software and in custom software developed for a particular installation.

remove background process or job

    The most common use of kill is simply to remove a process or job. This is done by naming the PID of the process (whcih is usually obtained with ps).

    $ kill PID

    This works because the default signal is SIGTERM (terminate the process).

discover signals

    You will find a chart of signals with the common signals for Linux, Mac OS X, and Solaris.

    You can also discover the list for your system by running kill with the -l (lower case L) option.

    $ kill -l

    You can determine a specific signal with the -l option and a signal number.

    $ kill -l 3
    QUIT
    $

    Some operating systems give the entire signal name with the SIG prefix (such as SIGQUIT) and some give just the signal name (such as SIGQUIT).

testing

    You can test the capabilities of your programs and scripts under abnormal coonditions by using kill to send a specific signal.

    $ kill -s SIGNAME PID

    The signal name (SIGNAME) can be the signal number or the signal name. The signal name can be either the signal name with or without the SIG prefix.

    You may also simply enter the signal number or signal name (with or without the SIG prefix) as an option.

    $ kill -6 PID
    $ kill -SIGIOT PID
    $ kill -IOT PID

other

    On November 8, 2010, Ramesh Natarajan named this the number 26 most frequently used Unix/Linux command at this web page 50 Most Frequently Used UNIX / Linux Commands (With Examples).

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