Updated: 2026-05-19

systemd service checks

systemd manages services: Nginx, certbot timer, applications, workers, and background jobs.

When a service “does not work”, do not restart everything immediately. Check state, recent errors, and dependencies first.

Check service status

sudo systemctl status nginx --no-pager

Look for:

• Active: active (running) — service is running;
• Active: failed — service failed;
• Loaded: — unit file was found;
• recent log lines at the bottom.

Check all failed units

sudo systemctl --failed

Empty list is good.

If a failed unit appears, inspect it:

sudo systemctl status service-name --no-pager

Check whether service starts on boot

sudo systemctl is-enabled nginx

Possible answers:

Start, stop, restart

sudo systemctl start nginx
sudo systemctl stop nginx
sudo systemctl restart nginx

Be careful with restart in production: it stops and starts the service.

Reload instead of restart

If a service supports reload, prefer it for config reloads:

sudo systemctl reload nginx

For Nginx:

sudo nginx -t
sudo systemctl reload nginx

If nginx -t fails, do not reload.

Read service logs

sudo journalctl -u nginx --no-pager -n 100

Follow logs:

sudo journalctl -u nginx -f

Last hour:

sudo journalctl -u nginx --since "1 hour ago" --no-pager

Check timers

For scheduled jobs:

sudo systemctl list-timers

For certbot:

sudo systemctl list-timers | grep certbot
sudo systemctl status certbot.timer --no-pager

If service does not start

Use this order:

sudo systemctl status service-name --no-pager
sudo journalctl -u service-name --no-pager -n 100
sudo systemctl cat service-name

Look for:

• wrong binary path;
• missing file permissions;
• port already in use;
• config error;
• missing environment variable;
• service exits immediately after start.

Check which port a service listens on

sudo ss -lntp | grep -E ':(80|443|7443)\b'

If a service should listen on a port but does not appear in ss, it did not start or is listening elsewhere.

Show unit file

sudo systemctl cat nginx

For custom overrides:

sudo systemctl cat service-name
sudo systemctl edit service-name

After changing unit files:

sudo systemctl daemon-reload
sudo systemctl restart service-name

Safe diagnostic order

sudo systemctl status service-name --no-pager
sudo journalctl -u service-name --no-pager -n 100
sudo systemctl --failed
sudo ss -lntp

Only after that decide: reload, restart, rollback, or config fix.

Common mistakes

Restarting without config test

Bad for Nginx:

sudo systemctl restart nginx

Better:

sudo nginx -t
sudo systemctl reload nginx

Ignoring failed units

If a service failed, systemctl --failed shows it faster than searching logs manually.

Checking the wrong service name

Find units:

systemctl list-units --type=service | grep -i nginx

Forgetting daemon-reload

After unit changes:

sudo systemctl daemon-reload

Otherwise systemd may still use the old unit definition.