在Centos上安裝docker后需要手動啟動docker服務，但是啟動時報如下錯誤
$ systemctl enable docker && systemctl start docker
A dependency job for docker.service failed. See 'journalctl -xe' for details.
執行 journalctl -xe后結果如下
$ journalctl -xe
1月 24 02:25:45 localhost.localdomain yum[18753]: 2:postfix-2.10.1-7.el7.x86_64: 100
1月 24 02:25:45 localhost.localdomain yum[18753]: fontconfig-2.13.0-4.3.el7.x86_64: 100
1月 24 02:26:12 localhost.localdomain polkitd[6691]: Registered Authentication Agent for unix-process:18768:232871247 (system bus na
1月 24 02:26:12 localhost.localdomain systemd[1]: Reloading.
1月 24 02:26:12 localhost.localdomain polkitd[6691]: Unregistered Authentication Agent for unix-process:18768:232871247 (system bus
1月 24 02:26:12 localhost.localdomain polkitd[6691]: Registered Authentication Agent for unix-process:18787:232871256 (system bus na
1月 24 02:26:12 localhost.localdomain systemd[1]: Starting Docker Socket for the API.
-- Subject: Unit docker.socket has begun start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit docker.socket has begun starting up.
1月 24 02:26:12 localhost.localdomain systemd[18793]: Failed to chown socket at step GROUP: No such process
1月 24 02:26:12 localhost.localdomain systemd[1]: docker.socket control process exited, code=exited status=216
1月 24 02:26:12 localhost.localdomain systemd[1]: Failed to listen on Docker Socket for the API.
-- Subject: Unit docker.socket has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit docker.socket has failed.
--
-- The result is failed.
1月 24 02:26:12 localhost.localdomain systemd[1]: Dependency failed for Docker Application Container Engine.
-- Subject: Unit docker.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit docker.service has failed.
--
-- The result is dependency.
1月 24 02:26:12 localhost.localdomain systemd[1]: Job docker.service/start failed with result 'dependency'.
1月 24 02:26:12 localhost.localdomain systemd[1]: Unit docker.socket entered failed state.
1月 24 02:26:12 localhost.localdomain polkitd[6691]: Unregistered Authentication Agent for unix-process:18787:232871256 (system bus
解決方案：添加docker組
$ groupadd docker
groupadd：無法打開 /etc/group
這里涉及到一個知識點就是文件隱藏屬性，使用lsattr查看文件隱藏屬性
$ lsattr /etc/group
----i--------e-- /etc/group
$ lsattr lsattr /etc/gshadow
----i--------e-- /etc/gshadow
這里的i屬性表示文件不能被刪除、改名，也不能寫入或添加數據，所以需要先去掉i屬性
$ chattr -i /etc/gshadow
$ chattr -i /etc/group
然后添加docker組，並啟動docker服務，systemctl enable docker是為了設置開機啟動docker服務
$ groupadd docker
$ systemctl enable docker && systemctl start docker
做過基線的同學應該知道，為了安全起見，最好還是把i屬性加回來
$ chattr +i /etc/gshadow
$ chattr +i /etc/group
參考