Recommended way of checking only one running service?

Question

I am writing a shell script to check if mongod server is running and if not, to start it. To acheive that I am using the below command:

systemctl is-active --quiet mongod

This does the job as expected. But it's possible my script will run on systems that do not have systemd, so I am interested in knowing whether there is a more portable way to do this.

Answer 1

This is not perfect, but will work on many systems. Note that the pgrep approach is suboptimal since the name might be slightly different, or you might pass a name that is a substring of another name, but it's a start.

#!/usr/bin/sh

if systemctl is-active --quiet "$1"  > /dev/null 2>&1; then
  echo "Running! (systemctl)"
elif service "$1" status  2>&1 | grep -Eq 'is running|: active (running)'; then
  echo "Running! (service)"
elif pgrep "$1" > /dev/null 2>&1 ; then
  echo "Running (pgrep)"
else
  echo "Not running"
fi

Save that as checkIfRunning and run it like this:

checkIfRunning mongod

Answer 2

There is no one, portable way of achieving that. But many current Linux distributions have old, legacy service command that behaves as a proxy to systemctl if run on systemd powered OS.

So you can run the command like this:

# service sshd status
Redirecting to /bin/systemctl status sshd.service
● sshd.service - OpenSSH server daemon
   Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled; vendor preset: enabled)
   Active: active (running) since Wed 2019-02-20 12:16:17 UTC; 1 weeks 2 days ago
     Docs: man:sshd(8)
           man:sshd_config(5)
 Main PID: 3388 (sshd)
   CGroup: /system.slice/sshd.service
           └─3388 /usr/sbin/sshd -D