check if the process is running and report failure if it is not.

sysmicuser · 03-27-2023, 11:22 PM

I have a python script running like the one below; it runs with albert user.

Code:

ps -fu albert|grep "server.py"
albert     24744   24615  0 11:34 ?        00:00:01 python server.py 8443

I have created a small snippet to check if the process is running and report failure if it is not.

Code:

cat check_process.sh
#!/bin/bash
set -x
APP_RUNNING=$(ps -fu albert|grep "server.py")

if [ -z "${APP_RUNNING}" ] ; then
    echo "App is not running, reporting exit 1"
    exit 1
else
  echo "App is running."
fi
./check_process.sh
++ ps -fu albert
++ grep server.py
+ APP_RUNNING='albert     24744   24615  0 11:34 ?        00:00:02 python server.py 8443'
+ '[' -z 'albert     24744   24615  0 11:34 ?        00:00:02 python server.py 8443' ']'
+ echo 'App is running
App is running

I am not able to figure out if
1. This is the best way to check if the process is running.

I see a lot on the internet people checking processes with pgrep, but it does not work for me.

I am not really much in shell scripting stuff but if there is any more brilliant/nicer/clean and tidy way that I can incorporate, I am super keen to hear from you.

Any guidance will be highly appreciated.

chrism01 · 03-28-2023, 12:27 AM

I'd be interested to know why pgrep 'doesn't work' for you.
It was created relatively recently (in Unix history) because so many people were writing potentially complex piped statements like yours .
For instance, you should also be adding ' |grep -v grep' to avoid a false match (think about it...).

sysmicuser · 03-28-2023, 01:05 AM

@chrism01
I will never require grep -v grep when I run ps -fu command? Maybe I would or rather I should if I was running "ps -ef". I am just telling based on my experience but kindly correct me if I am wrong.

When I do pgrep I don't get anything. Please check below

Code:

pgrep server.py
echo $?
1

Kindly assist.

scasey · 03-28-2023, 01:22 AM

The return code of 1 indicates that one or more processes matched the criteria. In other words, the program is running.
See man pgrep

pan64 · 03-28-2023, 02:31 AM

Quote:

Originally Posted by scasey

The return code of 1 indicates that one or more processes matched the criteria. In other words, the program is running.
See man pgrep

actually no, 1 means no process found.

Code:

EXIT STATUS
       0      One or more processes matched the criteria.
       1      No processes matched.
       2      Syntax error in the command line.
       3      Fatal error: out of memory etc.

but pgrep without -f will check the process name, which is python, so you ought to use pgrep -f server.py.
Even better would be to use a pid file.

MadeInGermany · 03-28-2023, 04:04 AM

Your sample

Code:

ps -fu albert | grep server.py

filters for user albert, so only if you run this as user albert you need a | grep -vw grep

Yes, pgrep is better.
pgrep by default takes the short ps name, in the case of "python server.py" it might be just "python" that is of course too unprecise.
pgrep -f
takes the full ps name.
pgrep -u albert
filters for user albert

Code:

pgrep -fu albert "server.py"

works like your sample but prints the pid(s), and can safely be run as user albert.

Consult the man page for further options

Code:

man pgrep

History:

pgrep and pkill were developed by Sun Microsystems for their Solaris, and re-engineered in Linux and some Unixes.
It takes many options that are known from ps and grep, so it is easy to use.

Another Linux command is pidof. pidof comes with some magic that might detect script names as well. But magic is hard to guess - I often need extensive test so generally prefer pgrep.