Start daemon process from cron job

Question

I have been trying for a few hours to do the following (on Centos 6):

1. cron starts process A
2. process A checks if process B is alive
3. if process B is not alive, process A starts process B

The problem is that after process A terminates, process B is terminated as well.

Process A and Process B are both bash running a script.

I have been trying to use bin/bash script.sh & and exec bin/bash script.sh both without success. If I start process A from the console, process B is not terminated.

Is what I am trying to do theoretically possible (e.g. have a process be started from a process launched from cron and have it survive). In which other ways could I start process B to have it survive the termination of process A?

Answer 1

use nohup scriptForB.sh inside scriptForA.sh... in that way, the child process will not be terminated when the parent process exits..

On termination, parent process will send SIGTERM signal to all child process. If you use nohup, the child process will ignore the SIGTERM signals.

Answer 2

I couldn't solve this problem but this is the workaround which worked for me:

1. I defined a new script run.sh which does something as the following:

   #!/bin/bash
   
   while true
   do
      run_process_a.sh
      sleep 60
   done
   

2. Then I defined a couple of other scripts

   • service.sh: A daemon script
   • start.sh: A wrapper to start an instance of run.sh and store its pid
   • stop.sh: A wrapper to stop an instance of run.sh through the stored pid

3. I registered service.sh with init.d and through chkconfig

As said, this is not a direct answer to my questions but it helped me solve my problem which is why I record it here. Also, this might be the cleaner approach to achieve what I intend.