本教程介绍如何使用systemctl工具列出启动失败的systemd管理的各个服务
列出启动失败的服务
[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'.
可以发现，有个一个服务启动失败了。
is-failed选项
可以使用is-failed选项检查指定的服务是否启动失败。如果启动失败，结果是failed。如果启动没有问题，结果是active。
[root@localhost ~]# systemctl is-failed httpd
failed
[root@localhost ~]# systemctl is-failed vsftpd
active
检查服务的状态
可以使用status选项，查看服务启动失败的原因，下面状态信息里面告诉我们，是httpd.conf配置文件354行有语法错误。
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查看服务的启动日志
如果使用systemctl status [unit]没有找到服务启动失败的原因，可以使用journalctl查看更多的启动日志。
下面操作是过滤出所有带有error的行，可以找到启动失败的服务。
[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]只查看某一个服务的启动日志：
[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.
#过滤出有错误的信息。
[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.
发现 /etc/httpd/conf/httpd.conf配置文件的354行，Directory标签没有关闭，返现原因了，就马上修改吧。
总结
我们学习了如何使用systemctl命令显示在Linux上运行失败的服务/单元。有关详细信息，请查看systemctl手册。
