Exercise: Services and boot review

Services and boot review

• Write, override, enable and check a custom service.
• Mask and disable services according to policy.
• Set the default target.

Before you start: reset the servers and complete this chapter's lessons. You work on servera as root (sudo -i); lab start and lab grade run on workstation. The grader checks the state of the running system and the files; a reboot is not required (but it is a good way to test that your changes last).

On servera:

1. Write /usr/local/bin/reporter.sh (mode 755) that appends a line containing the time and reporter alive to /var/log/reporter.log every ${INTERVAL:-10} seconds.
2. Write /etc/systemd/system/reporter.service: it runs the script, restarts it on failure, and is wanted by multi-user.target.
3. Use a drop-in, /etc/systemd/system/reporter.service.d/10-interval.conf, to set Environment=INTERVAL=2.
4. Enable and start reporter, and make sure it has written to its log.
5. Mask bluetooth.service, and stop and disable mdmonitor.service.
6. Make multi-user.target the default target.

Start the exercise

[student@workstation ~]$ lab start sa-systemd-review
[student@workstation ~]$ ssh student@servera
[student@servera ~]$ sudo -i
[root@servera ~]#

Write the script and the unit

[root@servera ~]# cat > /usr/local/bin/reporter.sh <<'EOT'
#!/bin/bash
while true; do
  echo "$(date +%T) reporter alive" >> /var/log/reporter.log
  sleep "${INTERVAL:-10}"
done
EOT
[root@servera ~]# chmod 755 /usr/local/bin/reporter.sh
[root@servera ~]# cat > /etc/systemd/system/reporter.service <<'EOT'
[Unit]
Description=Write a heartbeat line to a report file
After=network.target

[Service]
ExecStart=/usr/local/bin/reporter.sh
Restart=on-failure
RestartSec=2

[Install]
WantedBy=multi-user.target
EOT

Add the drop-in and start it

[root@servera ~]# mkdir -p /etc/systemd/system/reporter.service.d
[root@servera ~]# printf '[Service]\nEnvironment=INTERVAL=2\n' > /etc/systemd/system/reporter.service.d/10-interval.conf
[root@servera ~]# systemctl daemon-reload
[root@servera ~]# systemctl enable --now reporter
[root@servera ~]# systemctl status reporter | head -4
[root@servera ~]# tail -2 /var/log/reporter.log

systemctl cat reporter should show the unit followed by the drop-in.

Apply the service policy and the target

[root@servera ~]# systemctl mask bluetooth
[root@servera ~]# systemctl disable --now mdmonitor
[root@servera ~]# systemctl set-default multi-user.target
[root@servera ~]# systemctl get-default
multi-user.target

Grade

Leave servera, then on workstation:

Check your work with lab grade sa-systemd-review, then put the exercise away with lab finish sa-systemd-review.