Kill command


 
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# 1  
Old 03-24-2014
Kill command

what is the difference between kill 5 and kill %5? the first one is to kill a process with PID 5 but what does the % mean in the second one?
# 2  
Old 03-24-2014
It's a job id. It's only applicable when using the shell builtin version of kill. For detailed info, refer to your shell's man page -- specifically, the job control and kill builtin sections.

Regards,
Alister
# 3  
Old 03-24-2014
Quote:
Originally Posted by chinababy
what is the difference between kill 5 and kill %5? the first one is to kill a process with PID 5 but what does the % mean in the second one?

Kill %5 will kill the 5th background job, but kill 5 will kill the process with PID 5.Smilie
# 4  
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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