systemctl Command

The systemctl command is the primary interface for controlling the systemd system and service manager. It replaces older SysV init commands like service and chkconfig, providing unified management of system services, targets, and system state.

Syntax

systemctl [OPTIONS] COMMAND [UNIT...]

Core Service Management

Command	Description	Old Equivalent
systemctl start service	Start a service	service service start
systemctl stop service	Stop a service	service service stop
systemctl restart service	Restart a service	service service restart
systemctl reload service	Reload configuration	service service reload
systemctl status service	Show service status	service service status
systemctl enable service	Enable at boot	chkconfig service on
systemctl disable service	Disable at boot	chkconfig service off

Service Management Commands

Basic Operations

Start a service:

systemctl start nginx.service

Stop a service:

systemctl stop nginx.service

Restart a service:

systemctl restart nginx.service

Reload service configuration:

systemctl reload nginx.service

Check service status:

systemctl status nginx.service

Check if service is active:

systemctl is-active nginx.service

Enable/Disable Services

Enable service to start at boot:

systemctl enable nginx.service

Enable and start immediately:

systemctl enable --now nginx.service

Disable service from starting at boot:

systemctl disable nginx.service

Disable and stop immediately:

systemctl disable --now nginx.service

Service Information

List all services:

systemctl list-units --type=service

List all services including inactive:

systemctl list-units --type=service --all

List enabled services:

systemctl list-unit-files --type=service --state=enabled

List failed services:

systemctl --failed --type=service

Show service configuration:

systemctl cat nginx.service

System State Management

Power Management

Reboot the system:

systemctl reboot

Shutdown the system:

systemctl poweroff

Halt the system:

systemctl halt

Suspend the system:

systemctl suspend

Hibernate the system:

systemctl hibernate

Target Management

List current targets:

systemctl list-units --type=target

Change to specific target:

systemctl isolate graphical.target

Set default target:

systemctl set-default graphical.target

Get default target:

systemctl get-default

Unit Management

Common Target Levels

Target	Description	Equivalent
poweroff.target	System shutdown	Runlevel 0
rescue.target	Rescue mode	Runlevel 1
multi-user.target	Multi-user, no GUI	Runlevel 3
graphical.target	Multi-user with GUI	Runlevel 5
reboot.target	System reboot	Runlevel 6

Unit File Management

Create a new service:

sudo systemctl edit --full --force myservice.service

Edit service file:

sudo systemctl edit nginx.service

Reload systemd configuration:

systemctl daemon-reload

Reset service to defaults:

sudo systemctl edit nginx.service --remove

Job Management

Control System Jobs

List active jobs:

systemctl list-jobs

Cancel a job:

systemctl cancel job-id

Check system boot performance:

systemd-analyze

Analyze boot time:

systemd-analyze blame

Analyze critical chain:

systemd-analyze critical-chain

Advanced Usage

Service Dependencies

Show dependencies:

systemctl list-dependencies nginx.service

Show reverse dependencies:

systemctl list-dependencies --reverse nginx.service

Show unit requirements:

systemctl show --property=Requires nginx.service

Service Properties

Show all service properties:

systemctl show nginx.service

Show specific properties:

systemctl show -p CPUQuota,MemoryLimit nginx.service

Get main PID:

systemctl show --property=MainPID --value nginx.service

Masking Services

Mask a service (prevent manual start):

systemctl mask nginx.service

Unmask a service:

systemctl unmask nginx.service

Check if masked:

systemctl is-enabled nginx.service

Real-World Examples

Web Server Management

# Enable and start Apache
systemctl enable --now httpd

# Check Apache status
systemctl status httpd

# Reload Apache configuration
systemctl reload httpd

# Restart Apache with verbose output
systemctl restart --verbose httpd

Database Service Management

# Start MariaDB
systemctl start mariadb

# Enable MariaDB at boot
systemctl enable mariadb

# Check MariaDB status
systemctl status mariadb

# Check MariaDB logs
journalctl -u mariadb -f

System Diagnostics

# Check failed services
systemctl --failed

# List all running services
systemctl list-units --type=service --state=running

# Check system load
systemctl status

# Analyze boot performance
systemd-analyze

Service Troubleshooting

# Check service logs
journalctl -u service-name -b

# Start service in debug mode
systemctl edit service-name
# Add: Environment=SYSTEMD_LOG_LEVEL=debug

# Check service dependencies
systemctl list-dependencies service-name

# Verify service configuration
systemd-analyze verify service-name

Unit File Examples

Basic Service Template

[Unit]
Description=My Custom Service
After=network.target

[Service]
Type=simple
ExecStart=/usr/bin/mycommand
Restart=always
User=myuser

[Install]
WantedBy=multi-user.target

Web Service Template

[Unit]
Description=Web Application
After=network.target postgresql.service

[Service]
Type=forking
PIDFile=/var/run/myapp.pid
ExecStart=/usr/local/bin/myapp start
ExecStop=/usr/local/bin/myapp stop
User=www-data
Group=www-data

[Install]
WantedBy=multi-user.target

Integration with Other Tools

Monitoring Services

# Watch service status changes
watch systemctl status nginx.service

# Monitor service logs in real-time
journalctl -u nginx.service -f

# Check service resource usage
systemctl status nginx.service
# Look at CPU, Memory information

Automation Scripts

#!/bin/bash
# Service restart script

SERVICE="nginx"
if systemctl is-active --quiet $SERVICE; then
    echo "$SERVICE is running, restarting..."
    systemctl restart $SERVICE
else
    echo "$SERVICE is not running, starting..."
    systemctl start $SERVICE
fi

systemctl enable $SERVICE

Troubleshooting

Common Issues

Service fails to start:

# Check status
systemctl status service-name

# Check logs
journalctl -u service-name -b

# Check configuration
systemctl cat service-name

Service won't enable:

# Check dependencies
systemctl list-dependencies service-name

# Check target
systemctl get-default

# Verify unit file exists
systemctl list-unit-files | grep service-name

Performance issues:

# Check boot time
systemd-analyze blame

# Check service startup time
systemd-analyze critical-chain service-name

# Check resource limits
systemctl show service-name | grep Limit

Security Considerations

Service Hardening

Run as specific user:

[Service]
User=serviceuser
Group=servicegroup

Restrict capabilities:

[Service]
CapabilityBoundingSet=CAP_NET_BIND_SERVICE
AmbientCapabilities=CAP_NET_BIND_SERVICE

File system restrictions:

[Service]
ProtectSystem=full
ProtectHome=true
ReadWritePaths=/var/log/myservice

Best Practices

1. Always check status: Use systemctl status for diagnostics
2. Use --now with enable/disable: Changes take effect immediately
3. Test unit files: Use systemd-analyze verify before deploying
4. Monitor logs: Use journalctl for troubleshooting
5. Use templates: Create reusable service templates
6. Document dependencies: Clearly specify service dependencies
7. Security first: Use service hardening options

Migration from SysV

Conversion examples:

# Old SysV commands
service httpd start
chkconfig httpd on

# New systemd equivalents
systemctl start httpd
systemctl enable httpd

Migration checklist:

• Replace service commands with systemctl
• Update startup scripts to use targets
• Convert init scripts to unit files
• Update documentation and procedures
• Train administrators on new commands

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Content adapted from the linux-command project. Original content available at https://github.com/jaywcjlove/linux-command