> Don't confuse things that need action with those that take care of themselves.
Linux 中安装一些软件的时候，会自动在系统中创建相应的用户。比如 mysql、各种 display manager，以及我用来在家里实现 DLNA 视频点播的 minidlna 等等。然而当卸载这些软件的时候，当初自动创建的用户可能还留存在系统中，需要我们手动删除。这几天我就碰到了这样的例子。
连续几个月，我一直在开机日志中看到一句错误提示：
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4月 12 23:00:05 raawaa-desktop-arch systemd[1]: Starting Verify integrity of password and group files... 4月 12 23:00:05 raawaa-desktop-arch systemd[1]: Failed to start Verify integrity of password and group files.
google 了一番，知道了错误是 shadow.service 这个服务引起的，通过 systemctl status shadow.service 命令查看了一下该服务状态：
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● shadow.service - Verify integrity of password and group files Loaded: loaded (/usr/lib/systemd/system/shadow.service; static; vendor preset: disabled) Active: failed (Result: exit-code) since 二 2016-04-12 23:00:05 CST; 17min ago Process: 377 ExecStart=/usr/bin/pwck -r (code=exited, status=2) Main PID: 377 (code=exited, status=2)
4月 12 23:00:05 raawaa-desktop-arch systemd[1]: Starting Verify integrity of password and group files... 4月 12 23:00:05 raawaa-desktop-arch pwck[377]: user 'lightdm': directory '/var/lib/lightdm' does not exist 4月 12 23:00:05 raawaa-desktop-arch pwck[377]: pwck: no changes 4月 12 23:00:05 raawaa-desktop-arch systemd[1]: shadow.service: Main process exited, code=exited, status=2/INVALIDARGUMENT 4月 12 23:00:05 raawaa-desktop-arch systemd[1]: Failed to start Verify integrity of password and group files. 4月 12 23:00:05 raawaa-desktop-arch systemd[1]: shadow.service: Unit entered failed state. 4月 12 23:00:05 raawaa-desktop-arch systemd[1]: shadow.service: Failed with result 'exit-code'.