[RHEL7] systemd unit specifiers (e.g. %p) are not expanded for Exec* properties

Issue

• When creating a custom instantiated unit and specifying a specifier in the program in the Exec* properties, systemd fails to start the unit, as shown in the example below

  • Custom unit file /etc/systemd/system/myunit@.service

    [Unit]
    Description=My unit instance %I
    [Service]
    Type=oneshot
    ExecStart=/usr/local/bin/myunit_%I
    

  • Custom program /usr/local/bin/myunit_instance

    #!/bin/bash
    echo "This is $(basename $0)"
    

  • Execution is failing

    # systemctl daemon-reload
    # systemctl start myunit@instance
    Job for myunit@instance.service failed because the control process exited with error code. [...]
    # systemctl status myunit@instance
    ● myunit@instance.service - My unit instance instance
       Loaded: loaded (/etc/systemd/system/myunit@.service; static; vendor preset: disabled)
       Active: failed (Result: exit-code) since Fri 2019-01-11 09:35:24 CET; 5s ago
      Process: 6484 ExecStart=/usr/local/bin/myunit_%I (code=exited, status=203/EXEC)
     Main PID: 6484 (code=exited, status=203/EXEC)
    
    XXX systemd[1]: Starting My unit instance instance...
    XXX systemd[1]: myunit@instance.service: main process exited, code=exited, st...EXEC
    XXX systemd[1]: Failed to start My unit instance instance.
    [...]
    

    As we can see in the example above, systemd tried to execute /usr/local/bin/myunit_%I which doesn't exist.

• When creating a custom instantiated unit and specifying a specifier for other properties or other arguments of the Exec* properties, there is no issue, as shown in the example below

  • Custom unit file /etc/systemd/system/myunit_ok@.service

    [Unit]
    Description=My unit instance %I
    [Service]
    Type=oneshot
    ExecStart=/usr/local/bin/myunit %I
    

    In the example above, the %I specifier is not used as the executable name, but as an argument to the /usr/local/bin/myunit program.

  • Custom program /usr/local/bin/myunit

    #!/bin/bash
    echo "This is $(basename $0), called with argument '$1'"
    

  • Execution is a success

    # systemctl daemon-reload
    # systemctl start myunit_ok@instance
    # systemctl status myunit_ok@instance
    ● myunit_ok@instance.service - My unit instance instance
       Loaded: loaded (/etc/systemd/system/myunit_ok@.service; static; vendor preset: disabled)
       Active: inactive (dead)
    
    XXX systemd[1]: Starting My unit instance instance...
    XXX myunit[6871]: This is myunit, called with argument 'instance'
    XXX systemd[1]: Started My unit instance instance.