mjhjmtu

Os: debian9.

touch /home/test/test.log

There is a simple function write-date in /etc/profile.

write-date()
 date >> /home/test/test.log
 

Create a service running at reboot or shutdown.

vim /etc/systemd/system/test.service 

[Unit]
Description=Run command at shutdown
Before=shutdown.target reboot.target

[Service]
Type=oneshot
RemainAfterExit=true
ExecStart=/bin/bash /home/test/test.sh

[Install]
WantedBy=multi-user.target

The simple function write-date in /home/test/test.sh.

vim /home/test/test.sh
write-date

Enable the test.service.

sudo systemctl enable test.service

Reboot my pc and check log of test.service

sudo journalctl -u test
-- Logs begin at Thu 2018-02-01 00:03:59 HKT, end at Thu 2018-02-01 00:15:54 HKT. --
Feb 01 00:04:04 test systemd[1]: Starting Run command at shutdown...
Feb 01 00:04:05 test bash[438]: /home/test/test.sh: line 3: write-date: command not found
Feb 01 00:04:11 test systemd[1]: test.service: Main process exited, code=exited, status=127/n/a
Feb 01 00:04:11 test systemd[1]: Failed to start Run command at shutdown.
Feb 01 00:04:11 test systemd[1]: test.service: Unit entered failed state.
Feb 01 00:04:11 test systemd[1]: test.service: Failed with result 'exit-code'.

How to make the command in /etc/profile be found ?

cat -vet /home/test/test.sh
$
$
 write-date$
 $
$

You probably need to explicitly tell your service that it needs to source /etc/profile.

[Unit]
Description=Run command at shutdown
Before=shutdown.target reboot.target

[Service]
EnvironmentFile=-/etc/profile
Type=oneshot
RemainAfterExit=true
ExecStart=/bin/bash /home/test/test.sh

[Install]
WantedBy=multi-user.target

Note the EnvironmentFile line.