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I am writing this simply script which conver to into a daemon and run in the background. The script job is simple. And it need to monitor a process type say ls command process. And write it into a file for records.

My approach to this to just have a while true loop to constantly check for a process type using ps command. And if it detect it, it will append it to a file.

I was wondering if this is a bad approach to write this

my code as follow

while true
do 
   if [[ $(ps -aux | grep -w "ls") ]]
   then 
       #append to file
   fi 
done &
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  • 2
    You may want to add a sleep x command lest your script go berserk. And, did you consider the pgrep command in lieu of the ps | grep pipe? Be aware you may get a multiline output. Commented Jun 1, 2022 at 14:37
  • yes. I have implement those. Also for the multi line output, i have implement a for loop to go through the ps output first and filter duplicate before append to a file. Commented Jun 1, 2022 at 14:41
  • Is that always the same process, or do PIDs change? Commented Jun 1, 2022 at 15:03
  • Yes Pid will change in this case. Since very ls command will have a start and end. And each time pid will change which reflect on each ls command process Commented Jun 1, 2022 at 15:07

2 Answers 2

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You could

grep commandname /proc/*/comm

which, on my linux system, is a factor 2 - 3 faster than ps | grep or pgrep.

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  • Ok but the whole while loop concept is correct right ? like i am just curious if there are any other way to monitor processes. Ihave tried watch command , but iti s not good in scripting. Commented Jun 1, 2022 at 15:54
  • @yolocoolflash what "process" are you talking about? It's beginning to sound like it should be a daemon instead. Commented Jun 1, 2022 at 16:07
  • It is a daemon which call this script and run it in the background Commented Jun 1, 2022 at 16:35
  • But the core function is in this while loop script which monitor a process type constantly Commented Jun 1, 2022 at 16:36
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You suggest,

My approach to this to just have a while true loop to constantly check for a process type using ps command. And if it detect it, it will append it to a file.

If you're going to do that just search for the process name and append any match. (If there's no match, nothing will get output.)

while sleep 5
do
    ps -ef | grep -w '[l]s' >> matched.txt
done

Without knowing what you really want to achieve it's difficult to critique your approach. If you simply want to restart a process if it goes away, then consider using a systemd unit. If you want to record that a process exists you might be better off using lastcomm or another audit tool to capture the start and end times of the named process. In both cases you can abolish your busy loop and you'll not lose any short-lived process executions.

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  • I am using systemd unit combine with this bash script to monitor a command process. So when a command process is being exited, then notify it . Commented Jun 1, 2022 at 18:34
  • yes I need to create this project that monitor a passwd command process has been trigger by someone who login as root. As that operation or event is not where to be logged in any log file location. Commented Jun 1, 2022 at 19:08
  • That is why i create this little daemon script to monitor in the background. so it will keep monitor that command process for me. Commented Jun 1, 2022 at 19:09
  • "I need to create this project that monitor a passwd command process has been trigger by someone who login as root." is that what you want to do? There are far far easier and more reliable ways of doing that Commented Jun 1, 2022 at 20:22
  • "systemd unit combine with this bash script to monitor a command process. So when a command process is being exited, then notify it" why not have systemd tell you? It is the authoritative source of this information, and again there is then no need for this busy loop Commented Jun 1, 2022 at 20:23

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