如何在Ubuntu中查看systemd服务日志

Question

我有一个如下的服务文件：

[Unit]
Description=demo service
Requisite=mosquitto.service
BindsTo=mosquitto.service

[Service]
Type=simple
ExecStart=/usr/bin/python3 /home/john/Documents/source/demo.py
Restart=on-failure
RestartSec=30s
StandardOutput=null

[Install]
WantedBy=multi-user.target

此demo.service只调用python代码demo.py。当我使用sudo systemctl start demo.service启动服务时，它总是保持在auto-restart(failure)模式。

demo.service - demo service
   Loaded: loaded (/etc/systemd/system/demo.service; enabled; vendor preset: enabled)
   Active: activating (auto-restart) (Result: exit-code) since Mon 2020-08-17 12:13:37 BST; 23s ago
  Process: 4744 ExecStart=/usr/bin/python3 /home/john/Documents/source/demo.py
 Main PID: 4744 (code=exited, status=1/FAILURE)

我已经检查过syslog了，但是里面没有有用的信息。它只显示演示服务启动和停止的日志。

我可以从哪里获得它的日志，以了解服务没有启动的原因。请帮帮忙。谢谢

以下是来自journactl的日志

Aug 13 13:51:40 john systemd[1]: Started demo service.
Aug 13 13:51:40 john systemd[1]: demo.service: Main process exited, code=exited, status=1/FAILURE
Aug 13 13:51:40 john systemd[1]: demo.service: Failed with result 'exit-code'.
Aug 13 13:52:10 john systemd[1]: demo.service: Service hold-off time over, scheduling restart.
Aug 13 13:52:10 john systemd[1]: demo.service: Scheduled restart job, restart counter is at 2.
Aug 13 13:52:10 john systemd[1]: Stopped demo service.

Answer 1

要查看记录的stdout和stderr，可以使用journalctl命令：

sudo journalctl -u [service_name]