How to use systemctl and service commands to manage services in Linux system service management? - 面试题

Linux system service management is a core skill for operations engineers, mainly involving systemd and traditional init systems.

systemd service management:

systemctl start service: start service
systemctl stop service: stop service
systemctl restart service: restart service
systemctl reload service: reload configuration (without interrupting service)
systemctl status service: view service status
systemctl enable service: set service to start automatically on boot
systemctl disable service: cancel service auto-start on boot
systemctl is-enabled service: check if service is set to auto-start
systemctl list-units --type=service: list all services
systemctl list-unit-files --type=service: list all service files
systemctl daemon-reload: reload systemd configuration

Service configuration files:

Location: /etc/systemd/system/ or /usr/lib/systemd/system/
Example: /etc/systemd/system/nginx.service

Service configuration file format:

ini
[Unit]
Description=nginx service
After=network.target

[Service]
Type=forking
ExecStart=/usr/sbin/nginx
ExecReload=/bin/kill -s HUP $MAINPID
ExecStop=/bin/kill -s TERM $MAINPID
Restart=on-failure

[Install]
WantedBy=multi-user.target

Traditional init service management (SysVinit):

service service start: start service
service service stop: stop service
service service restart: restart service
service service status: view service status
chkconfig --list: list all services
chkconfig service on: set service to start automatically on boot
chkconfig service off: cancel service auto-start on boot

Service log management:

journalctl -u service: view logs for a specific service
journalctl -u service -f: view service logs in real-time
journalctl -u service --since today: view today's logs
journalctl -u service --since "2024-01-01" --until "2024-01-02": view logs for a specific time period
journalctl -p err: view error-level logs
/var/log/messages: main system log
/var/log/syslog: system log (Debian/Ubuntu)

Service troubleshooting:

Check service status: systemctl status service
View service logs: journalctl -u service
Check configuration file: cat /etc/systemd/system/service.service
Check port listening: ss -tulnp | grep service
Check process: ps aux | grep service
Manual startup test: directly run the service's executable

Service optimization:

Adjust startup order: use After and Wants directives
Set resource limits: use LimitCPU, LimitMEM and other directives
Configure auto-restart: Restart=on-failure, RestartSec=10s
Optimize startup time: use Type=simple or Type=notify