Exercise: Scripts and scheduling review

Scripts and scheduling review

• Write a script that validates arguments and sets exit statuses.
• Schedule it with cron.d, a personal crontab and a systemd timer.

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 runs your script as an ordinary user with several arguments and checks its output and exit status.

On servera:

1. Write /usr/local/bin/sa-report.sh (mode 755): for a directory argument it prints Directory: NAME, Files: N (regular files directly inside) and Bytes: N (their total size) and exits 0; without exactly one argument it prints Usage: … to standard error and exits 2; for a non-directory it prints … is not a directory to standard error and exits 1.
2. Create /etc/cron.d/sa-report to run it on /etc/ssh as root at 06:15 on weekdays.
3. Give student a crontab entry that runs /usr/bin/logger -t sa-heartbeat alive every 10 minutes.
4. Create sa-report.service (oneshot, runs the script on /etc) and sa-report.timer (daily at 02:30, Persistent=true), and enable the timer.

Start the exercise

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

The script

[root@servera ~]# cat > /usr/local/bin/sa-report.sh <<'EOT'
#!/bin/bash
# Report the number and size of the files directly inside a directory
if [ $# -ne 1 ]; then
  echo "Usage: $0 DIRECTORY" >&2
  exit 2
fi
dir=$1
if [ ! -d "$dir" ]; then
  echo "$dir is not a directory" >&2
  exit 1
fi
files=0
bytes=0
for f in "$dir"/*; do
  if [ -f "$f" ]; then
    files=$((files + 1))
    bytes=$((bytes + $(stat -c %s "$f")))
  fi
done
echo "Directory: $dir"
echo "Files: $files"
echo "Bytes: $bytes"
EOT
[root@servera ~]# chmod 755 /usr/local/bin/sa-report.sh
[root@servera ~]# sa-report.sh /etc/ssh
Directory: /etc/ssh
Files: 9
Bytes: 551646
[root@servera ~]# sa-report.sh; echo "rc=$?"
Usage: /usr/local/bin/sa-report.sh DIRECTORY
rc=2
[root@servera ~]# sa-report.sh /etc/hostname; echo "rc=$?"
/etc/hostname is not a directory
rc=1

The numbers depend on your system. Test as an ordinary user too: su - student -c '/usr/local/bin/sa-report.sh /etc/ssh'.

The cron jobs

[root@servera ~]# cat > /etc/cron.d/sa-report <<'EOT'
PATH=/usr/local/bin:/usr/bin:/bin
15 6 * * 1-5 root /usr/local/bin/sa-report.sh /etc/ssh >> /var/log/sa-report.log 2>&1
EOT
[root@servera ~]# echo '*/10 * * * * /usr/bin/logger -t sa-heartbeat alive' > /tmp/ct
[root@servera ~]# crontab -u student /tmp/ct
[root@servera ~]# crontab -u student -l
*/10 * * * * /usr/bin/logger -t sa-heartbeat alive

The timer

[root@servera ~]# cat > /etc/systemd/system/sa-report.service <<'EOT'
[Unit]
Description=Report on /etc

[Service]
Type=oneshot
ExecStart=/usr/local/bin/sa-report.sh /etc
EOT
[root@servera ~]# cat > /etc/systemd/system/sa-report.timer <<'EOT'
[Unit]
Description=Run the report daily

[Timer]
OnCalendar=*-*-* 02:30:00
Persistent=true

[Install]
WantedBy=timers.target
EOT
[root@servera ~]# systemctl daemon-reload
[root@servera ~]# systemctl enable --now sa-report.timer
[root@servera ~]# systemctl list-timers sa-report.timer --no-pager
[root@servera ~]# systemctl start sa-report.service && journalctl -u sa-report.service -n 3 --no-pager

Grade

Leave servera, then on workstation:

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