systemctl 启动 mongodb出现问题，是什么原因，或者怎么排查

Question

[root@VM_3_231_centos ~]# sudo systemctl status mongod
● mongod.service - High-performance, schema-free document-oriented database
   Loaded: loaded (/usr/lib/systemd/system/mongod.service; enabled; vendor preset: disabled)
   Active: failed (Result: exit-code) since 六 2017-03-18 22:16:39 CST; 44s ago
     Docs: https://docs.mongodb.org/manual
  Process: 2401 ExecStart=/usr/bin/mongod $OPTIONS run (code=exited, status=2)
  Process: 2399 ExecStartPre=/usr/bin/chmod 0755 /var/run/mongodb (code=exited, status=0/SUCCESS)
  Process: 2397 ExecStartPre=/usr/bin/chown mongod:mongod /var/run/mongodb (code=exited, status=0/SUCCESS)
  Process: 2396 ExecStartPre=/usr/bin/mkdir -p /var/run/mongodb (code=exited, status=0/SUCCESS)
 Main PID: 2401 (code=exited, status=2)

3月 18 22:16:39 VM_3_231_centos systemd[1]: Starting High-performance, schema-free document-oriented database...
3月 18 22:16:39 VM_3_231_centos systemd[1]: Started High-performance, schema-free document-oriented database.
3月 18 22:16:39 VM_3_231_centos systemd[1]: mongod.service: main process exited, code=exited, status=2/INVALIDARGUMENT
3月 18 22:16:39 VM_3_231_centos systemd[1]: Unit mongod.service entered failed state.
3月 18 22:16:39 VM_3_231_centos systemd[1]: mongod.service failed.

这里是mongod的status信息，显示不正常，但是怎么修复，或者还需要怎么做才能排查出原因？

Answer 1

1. 检查加载失败的Unit——systemctl list-units --failed

2. 查看配置文件——配置文件主要放在/usr/lib/systemd/system目录，使用cat命令查看: systemctl cat mongod.service

3. 找到启动的命令和参数以及日志文件的地址（下一步要用），直接使用命令和参数尝试启动，如果失败可以看到原因。

4. 从日志文件查找原因并修复。

Answer 2

请问怎么解决的？