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Full Discussion: Kill command
Top Forums UNIX for Dummies Questions & Answers Kill command Post 302894199 by rbatte1 on Monday 24th of March 2014 10:39:29 AM
Old 03-24-2014
A very harsh way to learn is the difference between kill %1 and kill 1

This should be fine:-
Code:
# sleep 100 &
[1]     5638
# jobs
[1] +  Running                 sleep 100 &
# ps -f
     UID   PID    PPID  C    STIME TTY       TIME COMMAND
    root 17654   17653  0 13:33:49 pts/tv    0:00 -ksh
    root 5638    17654  0 14:28:48 pts/tv    0:00 sleep 100
    root 5840    17654  1 14:29:27 pts/tv    0:00 ps -f
    root 17653   986    0 13:33:49 pts/tv    0:00 telnetd -b /etc/herald
# kill %1
[1] + Terminated               sleep 100 &
#

I need to make this next bit clear:-
Do not run this!
Code:
# sleep 100 &
[1]     5638
# jobs
[1] +  Running                 sleep 100 &
# ps -f
     UID   PID    PPID  C    STIME TTY       TIME COMMAND
    root 17654   17653  0 13:33:49 pts/tv    0:00 -ksh
    root 5638    17654  0 14:28:48 pts/tv    0:00 sleep 100
    root 5840    17654  1 14:29:27 pts/tv    0:00 ps -f
    root 17653   986    0 13:33:49 pts/tv    0:00 telnetd -b /etc/herald
# kill 1
.
.
.

.... or your server with fail in the instant. Not even a crash in most cases, it just fails.

Even process 5 may be very early and a very critical process. You may be lucky and process 5 may have already terminated, but it's very risky stuff all the same. If you are the root user, you can terminate any process, so single digit errors on a kill command can be catastrophic. Imagine terminating an application serving process, a database query or worse a critical database service sudo as pmon for Oracle or oinit for Informix etc.


With great power comes great responsibility and errors can cause irrevocable damage.


Robin
 

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KILL(1)                                                            User Commands                                                           KILL(1)

NAME
kill - send a signal to a process SYNOPSIS
kill [options] <pid> [...] DESCRIPTION
The default signal for kill is TERM. Use -l or -L to list available signals. Particularly useful signals include HUP, INT, KILL, STOP, CONT, and 0. Alternate signals may be specified in three ways: -9, -SIGKILL or -KILL. Negative PID values may be used to choose whole process groups; see the PGID column in ps command output. A PID of -1 is special; it indicates all processes except the kill process itself and init. OPTIONS
<pid> [...] Send signal to every <pid> listed. -<signal> -s <signal> --signal <signal> Specify the signal to be sent. The signal can be specified by using name or number. The behavior of signals is explained in sig- nal(7) manual page. -l, --list [signal] List signal names. This option has optional argument, which will convert signal number to signal name, or other way round. -L, --table List signal names in a nice table. NOTES Your shell (command line interpreter) may have a built-in kill command. You may need to run the command described here as /bin/kill to solve the conflict. EXAMPLES
kill -9 -1 Kill all processes you can kill. kill -l 11 Translate number 11 into a signal name. kill -L List the available signal choices in a nice table. kill 123 543 2341 3453 Send the default signal, SIGTERM, to all those processes. SEE ALSO
kill(2), killall(1), nice(1), pkill(1), renice(1), signal(7), skill(1) STANDARDS
This command meets appropriate standards. The -L flag is Linux-specific. AUTHOR
Albert Cahalan <albert@users.sf.net> wrote kill in 1999 to replace a bsdutils one that was not standards compliant. The util-linux one might also work correctly. REPORTING BUGS
Please send bug reports to <procps@freelists.org> procps-ng October 2011 KILL(1)
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