Linux systemctl Command
Linux Command ReferenceWhat is systemctl
systemctl is a command-line tool in Linux systems used to control the systemd system and service manager. As a core component of modern Linux distributions, it replaces the traditional init system and service commands.
Introduction to systemd
systemd is a system and service manager that:
- Runs as PID 1 (the first process to start)
- Responsible for starting, stopping, and managing all other processes
- Provides parallel startup capability, significantly speeding up system boot time
- Supports on-demand service startup
- Provides log collection functionality (via journald)
systemctl Basic Syntax
systemctl [选项] [命令] [单元名称]
Common Options
| Option | Description |
|---|---|
| -t, --type | Specify unit type (service, socket, device, etc.) |
| -a, --all | Show all units, including inactive ones |
| --state | Filter units by state |
| -l, --full | Show complete unit information |
| -H, --host | Operate on a remote host |
Service Management Commands
Start/Stop/Restart Services
Example
# Start service
sudo systemctl start [service name]
# Stop service
sudo systemctl stop [service name]
# Restart service
sudo systemctl restart [service name]
# Reload configuration (without restarting service)
sudo systemctl reload [service name]
sudo systemctl start [service name]
# Stop service
sudo systemctl stop [service name]
# Restart service
sudo systemctl restart [service name]
# Reload configuration (without restarting service)
sudo systemctl reload [service name]
View Service Status
Example
# View single service status
systemctl status [service name]
# View all running services
systemctl list-units --type=service --state=running
# View failed services
systemctl --failed
systemctl status [service name]
# View all running services
systemctl list-units --type=service --state=running
# View failed services
systemctl --failed
Enable/Disable Services
Example
# Enable service (auto-start on boot)
sudo systemctl enable [service name]
# Disable service (cancel auto-start on boot)
sudo systemctl disable [service name]
# Check if service is enabled
systemctl is-enabled [service name]
sudo systemctl enable [service name]
# Disable service (cancel auto-start on boot)
sudo systemctl disable [service name]
# Check if service is enabled
systemctl is-enabled [service name]
Unit File Management
Unit File Locations
- System units:
/usr/lib/systemd/system/ - Administrator custom units:
/etc/systemd/system/
Common Unit File Operations
Example
# Reload all unit files (needed after modifying configuration)
sudo systemctl daemon-reload
# Display unit file contents
systemctl cat [unit name]
# Edit unit file (creates an override file)
sudo systemctl edit [unit name] --full
sudo systemctl daemon-reload
# Display unit file contents
systemctl cat [unit name]
# Edit unit file (creates an override file)
sudo systemctl edit [unit name] --full
System State Management
System Power Management
Example
# Shut down
sudo systemctl poweroff
# Reboot
sudo systemctl reboot
# Suspend
sudo systemctl suspend
# Hibernate
sudo systemctl hibernate
sudo systemctl poweroff
# Reboot
sudo systemctl reboot
# Suspend
sudo systemctl suspend
# Hibernate
sudo systemctl hibernate
System Runlevels
Example
# Get current target (runlevel)
systemctl get-default
# Set default target
sudo systemctl set-default [target name]
# Switch target (takes effect immediately)
sudo systemctl isolate [target name]
systemctl get-default
# Set default target
sudo systemctl set-default [target name]
# Switch target (takes effect immediately)
sudo systemctl isolate [target name]
Common targets:
- graphical.target - graphical interface mode
- multi-user.target - multi-user text mode
- rescue.target - rescue mode
- emergency.target - emergency mode
Practical Examples
Example 1: Managing Nginx Service
Example
# Start Nginx
sudo systemctl start nginx
# Enable auto-start on boot
sudo systemctl enable nginx
# Check status
systemctl status nginx
# Test configuration then reload
sudo nginx -t # Test configuration first
sudo systemctl reload nginx
sudo systemctl start nginx
# Enable auto-start on boot
sudo systemctl enable nginx
# Check status
systemctl status nginx
# Test configuration then reload
sudo nginx -t # Test configuration first
sudo systemctl reload nginx
Example 2: Creating a Custom Service
- Create service file
/etc/systemd/system/myapp.service：
Example
[Unit]
Description=My Custom Application
After=network.target
[Service]
ExecStart=/usr/bin/python3 /opt/myapp/app.py
WorkingDirectory=/opt/myapp
User=myappuser
Group=myappgroup
Restart=always
[Install]
WantedBy=multi-user.target
Description=My Custom Application
After=network.target
[Service]
ExecStart=/usr/bin/python3 /opt/myapp/app.py
WorkingDirectory=/opt/myapp
User=myappuser
Group=myappgroup
Restart=always
[Install]
WantedBy=multi-user.target
- Enable and start the service:
Example
sudo systemctl daemon-reload
sudo systemctl enable myapp
sudo systemctl start myapp
sudo systemctl enable myapp
sudo systemctl start myapp
Troubleshooting Common Issues
Service Failed to Start
View detailed logs:
journalctl -u [服务名] -xe
Check dependencies:
systemctl list-dependencies [服务名]
Run in debug mode:
systemctl status [服务名] -l --no-pager
Performance Analysis
Example
# Show system boot time
systemd-analyze
# Show startup time of each service
systemd-analyze blame
# Generate boot-up diagram (requires graphical interface)
systemd-analyze plot > boot.svg
systemd-analyze
# Show startup time of each service
systemd-analyze blame
# Generate boot-up diagram (requires graphical interface)
systemd-analyze plot > boot.svg