systemd Introduction

systemd manages everything that runs on modern Linux: services, mounts, timers, and more. systemctl is how you control it.

Basic Service Management

Terminal

$# Check service status

$systemctl status nginx

● nginx.service - A high performance web server Active: active (running) since Mon 2025-01-14 10:00:00 UTC Main PID: 1234 (nginx)

$# Start a service

$sudo systemctl start nginx

$# Stop a service

$sudo systemctl stop nginx

$# Restart a service

$sudo systemctl restart nginx

$# Reload config without restart

$sudo systemctl reload nginx

Enable/Disable on Boot

Terminal

$# Start on boot

$sudo systemctl enable nginx

Created symlink /etc/systemd/system/multi-user.target.wants/nginx.service

$# Don't start on boot

$sudo systemctl disable nginx

$# Enable AND start now

$sudo systemctl enable --now nginx

Check Status

Terminal

$# Is it running?

$systemctl is-active nginx

active

$# Will it start on boot?

$systemctl is-enabled nginx

enabled

$# Is it failed?

$systemctl is-failed nginx

active

List Services

Terminal

$# All loaded services

$systemctl list-units --type=service

UNIT LOAD ACTIVE SUB DESCRIPTION cron.service loaded active running Regular background program... nginx.service loaded active running A high performance web server sshd.service loaded active running OpenSSH server daemon

$# Failed services only

$systemctl --failed

View Logs

Terminal

$# Logs for a service

$journalctl -u nginx

(all nginx logs)

$# Follow logs (like tail -f)

$journalctl -u nginx -f

(live log output)

$# Last 50 lines

$journalctl -u nginx -n 50

$# Since last boot

$journalctl -u nginx -b

journalctl is Powerful

journalctl replaces reading log files manually. It can filter by time, service, priority, and more.

Create a Service

Create /etc/systemd/system/myapp.service:

hljs ini

[Unit]
Description=My Application
After=network.target

[Service]
Type=simple
User=deploy
WorkingDirectory=/opt/myapp
ExecStart=/opt/myapp/bin/server
Restart=always
RestartSec=10

[Install]
WantedBy=multi-user.target

Then:

Terminal

$sudo systemctl daemon-reload

(reload unit files)

$sudo systemctl enable --now myapp

(enable and start)

Service Types

Type	Behavior
`simple`	Process in ExecStart is the service
`forking`	Process forks, parent exits
`oneshot`	Run once, then exit
`notify`	Service signals when ready

Restart Policies

Restart	When
`no`	Never restart
`always`	Always restart
`on-failure`	Only if failed
`on-abnormal`	Abnormal exit

Reload After Changes

Terminal

$# After editing a unit file

$sudo systemctl daemon-reload

$sudo systemctl restart myapp

System State

Terminal

$# Reboot

$sudo systemctl reboot

$# Shutdown

$sudo systemctl poweroff

$# Suspend

$sudo systemctl suspend

Practical: Node.js Service

hljs ini

# /etc/systemd/system/nodeapp.service
[Unit]
Description=Node.js Application
After=network.target

[Service]
Type=simple
User=deploy
Group=deploy
WorkingDirectory=/var/www/app
Environment=NODE_ENV=production
Environment=PORT=3000
ExecStart=/usr/bin/node server.js
Restart=on-failure
RestartSec=10
StandardOutput=syslog
StandardError=syslog
SyslogIdentifier=nodeapp

[Install]
WantedBy=multi-user.target

Terminal

$sudo systemctl daemon-reload

$sudo systemctl enable --now nodeapp

$sudo systemctl status nodeapp

● nodeapp.service - Node.js Application Active: active (running)

Knowledge Check

What does 'systemctl enable nginx' do?

Quick Reference

Command	Purpose
`systemctl start svc`	Start service
`systemctl stop svc`	Stop service
`systemctl restart svc`	Restart service
`systemctl status svc`	Check status
`systemctl enable svc`	Start on boot
`systemctl disable svc`	Don't start on boot
`journalctl -u svc`	View service logs
`systemctl daemon-reload`	Reload unit files

Key Takeaways

systemctl controls services
start/stop/restart for immediate control
enable/disable for boot behavior
journalctl -u service for logs
Create custom services in /etc/systemd/system/
Always daemon-reload after editing unit files

Next: environment variables and shell configuration.

systemd Introduction

systemd manages everything that runs on modern Linux: services, mounts, timers, and more. systemctl is how you control it.

Basic Service Management

Terminal

$# Check service status

$systemctl status nginx

● nginx.service - A high performance web server Active: active (running) since Mon 2025-01-14 10:00:00 UTC Main PID: 1234 (nginx)

$# Start a service

$sudo systemctl start nginx

$# Stop a service

$sudo systemctl stop nginx

$# Restart a service

$sudo systemctl restart nginx

$# Reload config without restart

$sudo systemctl reload nginx

Enable/Disable on Boot

Terminal

$# Start on boot

$sudo systemctl enable nginx

Created symlink /etc/systemd/system/multi-user.target.wants/nginx.service

$# Don't start on boot

$sudo systemctl disable nginx

$# Enable AND start now

$sudo systemctl enable --now nginx

Check Status

Terminal

$# Is it running?

$systemctl is-active nginx

active

$# Will it start on boot?

$systemctl is-enabled nginx

enabled

$# Is it failed?

$systemctl is-failed nginx

active

List Services

Terminal

$# All loaded services

$systemctl list-units --type=service

$# Failed services only

$systemctl --failed

View Logs

Terminal

$# Logs for a service

$journalctl -u nginx

(all nginx logs)

$# Follow logs (like tail -f)

$journalctl -u nginx -f

(live log output)

$# Last 50 lines

$journalctl -u nginx -n 50

$# Since last boot

$journalctl -u nginx -b

journalctl is Powerful

journalctl replaces reading log files manually. It can filter by time, service, priority, and more.

Create a Service

Create /etc/systemd/system/myapp.service:

hljs ini

[Unit]
Description=My Application
After=network.target

[Service]
Type=simple
User=deploy
WorkingDirectory=/opt/myapp
ExecStart=/opt/myapp/bin/server
Restart=always
RestartSec=10

[Install]
WantedBy=multi-user.target

Then:

Terminal

$sudo systemctl daemon-reload

(reload unit files)

$sudo systemctl enable --now myapp

(enable and start)

Service Types

Type	Behavior
`simple`	Process in ExecStart is the service
`forking`	Process forks, parent exits
`oneshot`	Run once, then exit
`notify`	Service signals when ready

Restart Policies

Restart	When
`no`	Never restart
`always`	Always restart
`on-failure`	Only if failed
`on-abnormal`	Abnormal exit

Reload After Changes

Terminal

$# After editing a unit file

$sudo systemctl daemon-reload

$sudo systemctl restart myapp

System State

Terminal

$# Reboot

$sudo systemctl reboot

$# Shutdown

$sudo systemctl poweroff

$# Suspend

$sudo systemctl suspend

Practical: Node.js Service

hljs ini

# /etc/systemd/system/nodeapp.service
[Unit]
Description=Node.js Application
After=network.target

[Service]
Type=simple
User=deploy
Group=deploy
WorkingDirectory=/var/www/app
Environment=NODE_ENV=production
Environment=PORT=3000
ExecStart=/usr/bin/node server.js
Restart=on-failure
RestartSec=10
StandardOutput=syslog
StandardError=syslog
SyslogIdentifier=nodeapp

[Install]
WantedBy=multi-user.target

Terminal

$sudo systemctl daemon-reload

$sudo systemctl enable --now nodeapp

$sudo systemctl status nodeapp

● nodeapp.service - Node.js Application Active: active (running)

Knowledge Check

What does 'systemctl enable nginx' do?

Quick Reference

Command	Purpose
`systemctl start svc`	Start service
`systemctl stop svc`	Stop service
`systemctl restart svc`	Restart service
`systemctl status svc`	Check status
`systemctl enable svc`	Start on boot
`systemctl disable svc`	Don't start on boot
`journalctl -u svc`	View service logs
`systemctl daemon-reload`	Reload unit files

Key Takeaways

systemctl controls services
start/stop/restart for immediate control
enable/disable for boot behavior
journalctl -u service for logs
Create custom services in /etc/systemd/system/
Always daemon-reload after editing unit files

Next: environment variables and shell configuration.