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Full Discussion: Monitor a long running process
Top Forums Shell Programming and Scripting Monitor a long running process Post 302419507 by alister on Friday 7th of May 2010 11:15:40 AM
Old 05-07-2010
Quote:
Originally Posted by sunpraveen
I usually use while loop to monitor any long running process as below:

Code:
while true
do
if [[ $(ps -ef | grep <long running process id> | wc -l) -eq 0 ]];
then
<do something>
break
else
<do something>
fi

In my opinion, this is a very poor approach, as it is very vulnerable to false positives. What if a different command with a different pid contains an argument that matches the pid being grepped for? This code will not detect that the monitored process has died/exited. What's much worse, however, is that depending on the kernel process scheduler and the shell implementation, the grep command's pid argument itself could trigger a false positive when groveling through the ps output (and given the way this code is structured, to test for equality to zero as failure, this could be happening often ... silently).

I would (perhaps melodramatically Smilie) characterize this as an indiscriminate grepping of ps output. When dealing with multicolumn output whose values can collide (the arguments field, for example, can conceivably contain a username/pid/ppid/...), it is safer and easier to constrain the match to a specific column using AWK. And, if applicable, use ps' output options to limit output only to the fields that are necessary. If you are grepping for a pid, why not use a ps output format that only prints pid?

Instead of ...
Code:
if [[ $(ps -ef | grep <long running process id> | wc -l) -eq 0 ]];

I would suggest ...
Code:
if ! [ $(ps -o pid= -p <long running process id>) ]

Or, you could grep|wc the output of "ps -o pid= -p <long running process id>", if that feels more familiar Smilie

Regards,
Alister
Last edited by alister; 05-07-2010 at 12:36 PM..
 

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LEARN ABOUT CENTOS

platform::shell

platform::shell(n)					       Tcl Bundled Packages						platform::shell(n)

__________________________________________________________________________________________________________________________________________________

NAME

       platform::shell - System identification support code and utilities

SYNOPSIS

       package require platform::shell ?1.1.4?

       platform::shell::generic shell
       platform::shell::identify shell
       platform::shell::platform shell
_________________________________________________________________

DESCRIPTION

       The platform::shell package provides several utility commands useful for the identification of the architecture of a specific Tcl shell.

       This  package  allows the identification of the architecture of a specific Tcl shell different from the shell running the package. The only
       requirement is that the other shell (identified by its path), is actually executable on the current machine.

       While for most platform this means that the architecture of the interrogated shell is identical to the architecture of  the  running  shell
       this  is  not generally true. A counter example are all platforms which have 32 and 64 bit variants and where a 64bit system is able to run
       32bit code. For these running and interrogated shell may have different 32/64 bit settings and thus different identifiers.

       For applications like a code repository it is important to identify the architecture of the shell which will  actually  run  the  installed
       packages, versus the architecture of the shell running the repository software.

COMMANDS

       platform::shell::identify shell
	      This command does the same identification as platform::identify, for the specified Tcl shell, in contrast to the running shell.

       platform::shell::generic shell
	      This command does the same identification as platform::generic, for the specified Tcl shell, in contrast to the running shell.

       platform::shell::platform shell
	      This command returns the contents of tcl_platform(platform) for the specified Tcl shell.

KEYWORDS

       operating system, cpu architecture, platform, architecture

platform::shell 						       1.1.4							platform::shell(n)
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