Efficiently find PIDs of many processes started by services

Question

I have a file with many service names, some of them are running, some of them aren't.

foo.service
bar.service
baz.service

I would like to find an efficient way to get the PIDs of the running processes started by the services (for the not running ones a 0, -1 or empty results are valid).

Desired output example:

foo.service:8484
bar.server:
baz.service:9447

(bar.service isn't running).

So far I've managed to do the following: (1)

cat t.txt | xargs -I {} systemctl status {} | grep 'Main PID' \
                                                | awk '{print $3}'

With the following output:

8484
9447

But I can't tell which service every PID belongs to.

(I'm not bound to use xargs, grep or awk.. just looking for the most efficient way).

So far I've managed to do the following: (2)

for f in `cat t.txt`; do
    v=`systemctl status $f | grep 'Main PID:'`;
    echo "$f:`echo $v | awk '{print \$3}'`";
done;

-- this gives me my desired result. Is it efficient enough?

Answer 1

I ran into similar problem and fount leaner solution:

systemctl show --property MainPID --value $SERVICE

returns just the PID of the service, so your example can be simplified down to

for f in `cat t.txt`; do
    echo "$f:`systemctl show --property MainPID --value $f`";
done