本教程介紹如何使用systemctl工具列出啓動失敗的systemd管理的各個服務
列出啓動失敗的服務
[root@localhost ~]# systemctl list-units --state failed
UNIT LOAD ACTIVE SUB DESCRIPTION
● httpd.service loaded failed failed The Apache HTTP Server
LOAD = Reflects whether the unit definition was properly loaded.
ACTIVE = The high-level unit activation state, i.e. generalization of SUB.
SUB = The low-level unit activation state, values depend on unit type.
1 loaded units listed. Pass --all to see loaded but inactive units, too.
To show all installed unit files use 'systemctl list-unit-files'.
is-failed選項
可以使用is-failed選項檢查指定的服務是否啓動失敗。如果啓動失敗，結果是failed。如果啓動沒有問題，結果是active。
[root@localhost ~]# systemctl is-failed httpd
failed
[root@localhost ~]# systemctl is-failed vsftpd
active
檢查服務的狀態
可以使用status選項，查看服務啓動失敗的原因，下面狀態信息裏面告訴我們，是httpd.conf配置文件354行有語法錯誤。
May 26 09:22:05 localhost httpd[2958]: httpd: Syntax error on line 354 of /etc/httpd/conf/httpd.conf: /...osed.
[root@localhost ~]# systemctl status httpd
● httpd.service - The Apache HTTP Server
Loaded: loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset: disabled)
Active: failed (Result: exit-code) since Tue 2020-05-26 09:22:05 CST; 18min ago
Docs: man:httpd(8)
man:apachectl(8)
Main PID: 2958 (code=exited, status=1/FAILURE)
May 26 09:22:05 localhost systemd[1]: Starting The Apache HTTP Server...
May 26 09:22:05 localhost httpd[2958]: httpd: Syntax error on line 354 of /etc/httpd/conf/httpd.conf: /...osed.
May 26 09:22:05 localhost systemd[1]: httpd.service: main process exited, code=exited, status=1/FAILURE
May 26 09:22:05 localhost kill[2959]: kill: cannot find process ""
May 26 09:22:05 localhost systemd[1]: httpd.service: control process exited, code=exited status=1
May 26 09:22:05 localhost systemd[1]: Failed to start The Apache HTTP Server.
May 26 09:22:05 localhost systemd[1]: Unit httpd.service entered failed state.
May 26 09:22:05 localhost systemd[1]: httpd.service failed.
Hint: Some lines were ellipsized, use -l to show in full.
使用journalctl查看服務的啓動日誌
如果使用systemctl status [unit]沒有找到服務啓動失敗的原因，可以使用journalctl查看更多的啓動日誌。
下面操作是過濾出所有帶有error的行，可以找到啓動失敗的服務。
[root@localhost ~]# journalctl |grep 'error'
May 26 09:22:05 localhost httpd[2958]: httpd: Syntax error on line 354 of /etc/httpd/conf/httpd.conf: /etc/httpd/conf/httpd.conf:354: was not closed.
也可以使用journalctl -u [unit]只查看某一個服務的啓動日誌：
[root@localhost ~]# journalctl -u httpd.service
-- Logs begin at Sun 2020-05-24 06:52:52 CST, end at Tue 2020-05-26 09:48:03 CST. --
May 26 09:22:05 localhost systemd[1]: Starting The Apache HTTP Server...
May 26 09:22:05 localhost httpd[2958]: httpd: Syntax error on line 354 of /etc/httpd/conf/httpd.conf: /etc/httpd/conf/httpd.conf:354: was not closed.
May 26 09:22:05 localhost systemd[1]: httpd.service: main process exited, code=exited, status=1/FAILURE
May 26 09:22:05 localhost kill[2959]: kill: cannot find process ""
May 26 09:22:05 localhost systemd[1]: httpd.service: control process exited, code=exited status=1
May 26 09:22:05 localhost systemd[1]: Failed to start The Apache HTTP Server.
May 26 09:22:05 localhost systemd[1]: Unit httpd.service entered failed state.
May 26 09:22:05 localhost systemd[1]: httpd.service failed.
#過濾出有錯誤的信息。
[root@localhost ~]# journalctl -u httpd.service |grep 'error'
May 26 09:22:05 localhost httpd[2958]: httpd: Syntax error on line 354 of /etc/httpd/conf/httpd.conf: /etc/httpd/conf/httpd.conf:354: was not closed.
發現
/etc/httpd/conf/httpd.conf配置文件的354行，Directory標籤沒有關閉，返現原因了，就馬上修改吧。
總結
我們學習瞭如何使用systemctl命令顯示在Linux上運行失敗的服務/單元。有關詳細信息，請查看systemctl手冊。