Determining how specific services were started?

Question

I have a Raspberry Pi which is running well, and am looking at creating a status app for it. I have some services that are run on startup, and I want my app to check that they are running, and if not then start them (or offer the option for me to attempt to start them).

But from what I can tell there are multiple ways to start/stop/check status of services, eg systemctl, service, possibly others that I don't recall right now.

How can I determine how any specified service was started, or to put it another way, what commands I should use if I wanted to start/stop/check my services?

Running Raspbian Stretch on a Pi 3b+

Answer 1

To check the status of services you can use the power of systemctl. For example you can query for all active systemd units with:

rpi ~$ systemctl --state=active --no-legend list-units systemd-*
systemd-ask-password-console.path  loaded active waiting   Dispatch Password Requests to Console Directory Watch
systemd-ask-password-wall.path     loaded active waiting   Forward Password Requests to Wall Directory Watch
[email protected] loaded active exited    File System Check on /dev/mmcblk0p1
systemd-journal-flush.service      loaded active exited    Flush Journal to Persistent Storage
systemd-journald.service           loaded active running   Journal Service
systemd-logind.service             loaded active running   Login Service
systemd-modules-load.service       loaded active exited    Load Kernel Modules
systemd-random-seed.service        loaded active exited    Load/Save Random Seed
systemd-remount-fs.service         loaded active exited    Remount Root and Kernel File Systems
systemd-sysctl.service             loaded active exited    Apply Kernel Variables
systemd-sysusers.service           loaded active exited    Create System Users
systemd-timesyncd.service          loaded active running   Network Time Synchronization
systemd-tmpfiles-setup-dev.service loaded active exited    Create Static Device Nodes in /dev
systemd-tmpfiles-setup.service     loaded active exited    Create Volatile Files and Directories
systemd-udev-trigger.service       loaded active exited    udev Coldplug all Devices
systemd-udevd.service              loaded active running   udev Kernel Device Manager
systemd-update-utmp.service        loaded active exited    Update UTMP about System Boot/Shutdown
systemd-user-sessions.service      loaded active exited    Permit User Sessions
systemd-fsckd.socket               loaded active listening fsck to fsckd communication Socket
systemd-initctl.socket             loaded active listening initctl Compatibility Named Pipe
systemd-journald-dev-log.socket    loaded active running   Journal Socket (/dev/log)
systemd-journald.socket            loaded active running   Journal Socket
systemd-rfkill.socket              loaded active listening Load/Save RF Kill Switch Status /dev/rfkill Watch
systemd-udevd-control.socket       loaded active running   udev Control Socket
systemd-udevd-kernel.socket        loaded active running   udev Kernel Socket
systemd-tmpfiles-clean.timer       loaded active waiting   Daily Cleanup of Temporary Directories

You can query for --all units instead of --state=active. Then you will see what states are available that you can ask with --state=, for example inactive. Or just restrict it to one service with:

rpi ~$ systemctl --no-legend list-units systemd-timesyncd.service
systemd-timesyncd.service loaded active running Network Time Synchronization

Have a look at systemctl --help or man systemctl for many other query options.

If you decide to use systemctl from the command line, maybe in a system call from your application, then you also can use all its other options, e.g. to start/stop services with:

rpi ~$ sudo systemctl start/stop my.service

But because you want to make an application I strongly recommend to use the programming API of systemd. It uses the dbus as interface. You can look at The D-Bus API of systemd/PID 1 how to use it with your program.

Answer 2

You can use this bash code and call this script with sudo:

#!/bin/bash

SERVICE_PID_NAME="apache2";
if [ -z "$(pidof ${SERVICE_PID_NAME})" ];then
  echo "[!] service ${SERVICE_PID_NAME} is not running...";
  echo "I'm starting the service ${SERVICE_PID_NAME}";
  systemctl start ${SERVICE_PID_NAME}
else
  echo "[+] service ${SERVICE_PID_NAME} is already running...";
fi;

Adjust the SERVICE_PID_NAME variable with your own process name.