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Full Discussion: Process existence or/and permission
Top Forums Shell Programming and Scripting Process existence or/and permission Post 302999688 by chebarbudo on Monday 26th of June 2017 09:33:01 AM
Old 06-26-2017
Process existence or/and permission
Hi,

In a bash script, I'm using kill -0 to test if I have permission to kill a process. There are 3 cases:
- the process exists and I have permission: OK
- the process doesn't exist and it's OK (because I decided to ignore processes that are already dead).
- I don't have permission and I want to raise an error.

If I use ps $pid, I cannot tell the difference between a process that does not exist and a process I cannot "see":
Code:
santiago@alphard:~$ ps 1 > /dev/null && echo OK || echo ERR
ERR
santiago@alphard:~$ sudo ps 1 > /dev/null && echo OK || echo ERR
OK

If I use kill -0 $pid, I could tell the difference reading stderr but it would be language specific:
Code:
santiago@alphard:~$ for pid in 1 123; do for lc in C fr_FR.utf-8; do LC_ALL=$lc; kill -0 $pid; echo Status is $?; done; done
-su: kill: (1) - Operation not permitted
Status is 1
-su: kill: (1) - Opération non permise
Status is 1
-su: kill: (123) - No such process
Status is 1
-su: kill: (123) - Aucun processus de ce type
Status is 1

Question: How can I programmatically tell if a process exists and if I have permission on it?

Regards
Santiago
 

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LEARN ABOUT PHP

kill

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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