systemd env vars from an executable script - linux

Question

I have the following systemd service file:
[Unit]
Description=My description
[Service]
Type=simple
User=myuser
ExecStart=/path/to/my/start_script.sh
ExecStop=/path/to/my/stop_script.sh
ExecReload=/bin/kill -HUP $MAINPID
KillMode=process
Restart=on-failure
RestartSec=30s
[Install]
WantedBy=multi-user.target
My start_script.sh is used to start a java application BUT I need to get some variables from an executable ksh script custom_script.sh.
I tried the following systemd params with no success:
ExecStartPre
EnvironmentFile
Is there a way to make it work?
Thank you in advance heroes.

Answer 1

In order to have the variables from custom_script.sh accessible from your Java process, you'll have to insert them into the environment somehow, in a way that systemd will be pleased with. The docs for the EnvironmentFile= directive say that any line that is not a parameter assignment statement with an = sign will be ignored. So we need to take your script and cook it down so that all we have left are the variables after running it.
What you can do is create an auxiliary "distillery" service that sources your custom_script.sh file and prints every value in the environment to another file called custom_script.env. Then you can provide the "distilled" environment file to the Java process in the EnvironmentFile directive.
So if your original service adds After= and Requires= like this,
[Unit]
Description=My description
After=custom-script-distillery
Requires=custom-script-distillery
[Service]
Type=simple
User=myuser
EnvironmentFile=/path/to/my/custom_script.env
ExecStart=/path/to/my/start_script.sh
ExecStop=/path/to/my/stop_script.sh
ExecReload=/bin/kill -HUP $MAINPID
KillMode=process
Restart=on-failure
RestartSec=30s
[Install]
WantedBy=multi-user.target
Then the distillery could look like this:
[Unit]
Description=My service to distill custom_script.sh to an EnvironmentFile
[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/bin/bash -c 'set -o allexport; source /path/to/my/custom_script.sh; set +o allexport; unset IFS; set | grep -v "^BASH" > /path/to/my/custom_script.env'