| Tested on | RHEL 10.2 (Coughlan) — vm1.lab.example |
|---|---|
| Package | systemd 257-23.el10_2.2 |
| Applies to | Ubuntu, Debian, Kali Linux, Linux Mint, Pop!_OS, Raspberry Pi OS, elementary OS, Zorin OS, Parrot OS, MX Linux, RHEL, Rocky Linux, AlmaLinux, Oracle Linux, CentOS Stream, Fedora, Arch Linux |
| Privilege | sudo or root |
| Scope | Pair a oneshot service with a timer using OnBootSec for a boot delay, enable only the timer, inspect list-timers, and read the script output file. Does not cover calendar schedules or cron migration. |
| Related guides | systemd timers Run script at boot after network crontab command Create a systemd service systemctl command |
When you need a script to run several minutes after boot — not at the first second of multi-user.target — use two unit files: a timer that waits and a service that runs your script.
boot
↓
delayed-boot-task.timer (waits 5 minutes)
↓
delayed-boot-task.service
↓
your scriptThe .timer decides when to run. The .service decides what to run.
Create the script
Write a script that logs when the timer fires:
sudo tee /usr/local/sbin/delayed-boot-task.sh <<'EOF'
#!/bin/bash
echo "time=$(date -Is) delayed_boot_task ran" >> /var/log/delayed-boot-task.log
EOFMake it executable:
sudo chmod 755 /usr/local/sbin/delayed-boot-task.shCreate the service unit
Create /etc/systemd/system/delayed-boot-task.service:
[Unit]
Description=Run delayed boot task once
[Service]
Type=oneshot
ExecStart=/usr/local/sbin/delayed-boot-task.shYou do not enable this service directly. The timer starts it when the delay expires, so only the .timer file needs an [Install] section.
Do not put a [Timer] section here. A [Timer] section belongs only in a .timer unit; putting it in a .service file produces an Unknown section 'Timer' warning or error and the timer settings are ignored.
Create the timer unit
Create /etc/systemd/system/delayed-boot-task.timer:
[Unit]
Description=Run delayed boot task five minutes after boot
[Timer]
OnBootSec=5min
Unit=delayed-boot-task.service
[Install]
WantedBy=timers.targetOnBootSec=5min means five minutes after machine boot time. It is measured from boot, not from when you enable the timer. Change 5min to any supported span (90s, 10min, 1h 30min, and so on).
Reload and enable the timer
Reload unit definitions after creating both files:
sudo systemctl daemon-reloadEnable the timer — not the service:
sudo systemctl enable delayed-boot-task.timerSample output:
Created symlink '/etc/systemd/system/timers.target.wants/delayed-boot-task.timer' → '/etc/systemd/system/delayed-boot-task.timer'.Plain enable schedules the timer for future boots. It does not start the timer in the current boot unless you also run systemctl start delayed-boot-task.timer or systemctl enable --now delayed-boot-task.timer.
Verify the next trigger
Reboot, then check when the timer will fire:
systemctl list-timers delayed-boot-task.timer --no-pagerSample output shortly after boot:
NEXT LEFT LAST PASSED UNIT ACTIVATES
Fri 2026-08-21 11:19:43 IST 4min 48s left - - delayed-boot-task.timer delayed-boot-task.service
1 timers listed.The LEFT column is the countdown until your script runs.
After five minutes, the same command shows the timer as elapsed and lists a LAST time instead of NEXT.
Confirm the script ran
Read the log file the script writes:
sudo cat /var/log/delayed-boot-task.logSample output:
time=2026-08-21T11:19:43+05:30 delayed_boot_task ranUse the timestamp to confirm which run you are looking at.
Troubleshooting
| Symptom | Likely cause | Fix |
|---|---|---|
Unknown section 'Timer' |
[Timer] inside .service |
Move schedule to .timer file |
| Service runs immediately during testing | Timer started after OnBootSec= elapsed |
Expected for current boot; full delay applies when the timer starts during boot on the next cycle |
| Timer enabled but nothing on current boot | enable alone does not start the timer |
Use systemctl start or enable --now to activate in the running boot |
| Timer active but no script | Name mismatch | Set Unit= in timer or match basenames |
| No second run during the same boot | OnBootSec= fires once per boot |
Expected — use OnUnitActiveSec= in systemd timers guide for repeated runs |
References
Summary
A boot delay needs two files: the timer holds OnBootSec= and the [Install] section; the service holds ExecStart=. Enable only the timer.
Use systemctl list-timers to watch the countdown, then confirm the script log after the trigger fires. For repeating schedules or calendar times, see the full systemd timers guide.
