systemctl¶

此外，我们使用 systemctl status service-name 常常会看到过长的日志被截断，所以我们需要一个 -l 参数来防止truncate:

systemctl -l status service-name

列出units¶

要检查有哪些服务已经安装，可以执行:
```
systemctl list-unit-files --type service
```

输出类似:

UNIT FILE                                  STATE           VENDOR PRESET
alsa-restore.service                       static          -
alsa-state.service                         static          -
alsa-utils.service                         masked          enabled
apache-htcacheclean.service                disabled        disabled
...

可以进一步列出状态是 running 的服务:

systemctl list-units --type=service --state=running

由于服务之间有依赖，我们可以显示出这个关系:
```
systemctl list-dependencies <service_unit_file>
```

例如:

systemctl list-dependencies mysqld

显示输出类似:

mysqld.service
● ├─system.slice
● └─sysinit.target
●   ├─dev-hugepages.mount
●   ├─dev-mqueue.mount
...

检查失败的单元¶

有些服务从一开始操作系统启动就是失败的，我们通过以下命令检查:
```
systemctl --failed
```

输出可能类似:

UNIT               LOAD   ACTIVE SUB    DESCRIPTION
● lightdm.service    loaded failed failed Light Display Manager
● networking.service loaded failed failed Raise network interfaces

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.
2 loaded units listed.

以上案例中2个没有正常启动的服务，我们可以排查

激活单元¶

为了在操作系统启动时运行服务，我们要激活 enable 服务。

检查服务是否激活:

systemctl is-enabled <service_unit_file>.service

举例:

systemctl is-enabled rsyslog.service

输出可能是 enabled

systemd-analyze¶

systemd-analyze 提供了启动过程的时间统计信息:
```
systemd-analyze
```

输出显示类似:

Startup finished in 1.801s (kernel) + 15.286s (userspace) = 17.088s
graphical.target reached after 15.212s in userspace

可以检查启动过程每个服务单元花费时间:
```
systemd-analyze blame
```