[systemd-devel] Starting one service when another one starts

[Nick Howitt]

Hi,
I apologise if this is not the right place for user help. If it is not, 
please point me to the best place.

I am trying to start a service (clearshare-scheduler) when another 
service (siad) starts. Clearshare-scheduler is an odd service. When you 
start it it may run for ages (days+) or it may terminate immediately so 
I have set it up as a oneshot:

[Unit]
Description=Clearshare Scheduler
PartOf=siad.service
After=siad.service

[Service]
Type=oneshot
Environment="TERM=dumb"
ExecStartPre=-/usr/bin/killall -15 -q /usr/sbin/clearshare-scheduler.sh
ExecStartPre=-/usr/bin/echo "$(/usr/bin/date) Starting scheduler from 
systemd" >> /var/log/scheduler.log
ExecStart=/usr/sbin/clearshare-scheduler.sh > /dev/null
ExecStop=-/usr/bin/killall -15 -q /usr/sbin/clearshare-scheduler.sh

[Install]
WantedBy=multi-user.target

The siad service looks like:

[Unit]
Description=Siad
After=syslog.target network.target clearsync.service

[Service]
Type=simple
OOMScoreAdjust=500
PIDFile=/var/run/siad.pid
EnvironmentFile=/etc/sysconfig/siad
Environment="SIA_DATA_DIR=/var/lib/siad-data"
ExecStartPre=-/usr/bin/killall -15 -q clearshare-scheduler.sh
ExecStartPre=-/usr/bin/rm -f /var/run/siad.pid
ExecStart=/usr/bin/siad $EXTRA_ARGS
ExecStop=/usr/bin/siac stop
WorkingDirectory=/var/lib/sia/
ExecStartPost=/usr/bin/sh -c 'umask 022; /usr/bin/pgrep siad > 
/var/run/siad.pid'

[Install]
WantedBy=multi-user.target

A "systemctl show clearshare-scheduler" lists the PartOf=siad.service as 
one of its properties but, in reverse, "systemctl show siad" does not 
list the corresponding ConsistsOf property.

When I start siad, nothing happens to the clearshare-scheduler service. 
It does not try to start but it runs when I run it on its own. Have I 
misunderstood something?

My version of systems is systemd-219-78.el7_9.5.

Thanks,

Nick