systemd doesn't run an application from bash script

Question

I have a service that should run set of applications in background on my Yocto embedded Linux system. I don't like an idea to create a systemd startup script for each app so I just run them from a bash script as following:

The service:

startup.service

[Unit]
Description=applications startup script
After=network.target

[Service]
Type=simple
ExecStart=/opt/somedir/startup.sh

[Install]
WantedBy=multi-user.target

and the script

startup.sh

#!/bin/bash

echo "application startup script"
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/opt/somedir
/opt/somedir/app1 &
/opt/somedir/app2 &
/opt/somedir/app3 &

But no application started. Checking the service status give me:

systemctl status startup

● startup.service - applications startup script
   Loaded: loaded (/lib/systemd/system/startup.service; enabled; vendor preset: enabled)
   Active: inactive (dead) since Thu 2021-03-25 10:33:16 UTC; 18min ago
  Process: 428 ExecStart=/opt/somedir/startup.sh (code=exited, status=0/SUCCESS)
 Main PID: 428 (code=exited, status=0/SUCCESS)

Mar 25 10:33:16 systemd[1]: Started application startup script.
Mar 25 10:33:16 startup.sh[428]: application startup script
Mar 25 10:33:16 systemd[1]: startup.service: Succeeded.

So the service executed on the system startup and executes the script. If I execute the script from the command line it starts the applications as expected. So what a reason that no application run?

Answer 1

Systemd will need to know how to run the script. Therefore either add:

#!/bin/bash

to the top line of the startup.sh script or change the ExecStart line in the systemd service file to:

ExecStart=/bin/bash -c /opt/somedir/startup.sh

Also, to ensure that the processes spawned remain persistent after being spawned, change:

Type=forking

Answer 2

systemd runs script startup.sh , and after that process ends, it assumes all is done so it kills off any remaining processes and the unit ends. The simplest solution is to add a wait at the end of startup.sh so that it only returns when the backgrounded processes have all ended.