Systemd Service Mask¶

我在 Jetson Nano快速起步构建一个工作环境，采用 NetworkManager 来实现无线网络配置。最近，我发现 Jetson Nano 升级重启后，无线网络没有激活。

检查 NetworkManager 服务:
```
systemctl status NetworkManager
```

输出显示服务没有启动:

● NetworkManager.service - Network Manager
   Loaded: loaded (/lib/systemd/system/NetworkManager.service; masked; vendor preset: enabled)
   Active: inactive (dead)
     Docs: man:NetworkManager(8)

启动服务:
```
systemctl start NetworkManager
```

可以看到服务能够正常启动，再次检查 systemctl status NetworkManager 也可以看到服务正常运行:

● NetworkManager.service - Network Manager
   Loaded: loaded (/lib/systemd/system/NetworkManager.service; masked; vendor preset: enabled)
   Active: active (running) since Tue 2021-06-01 15:37:26 CST; 7s ago
     Docs: man:NetworkManager(8)
 Main PID: 27815 (NetworkManager)
    Tasks: 5 (limit: 4181)
   CGroup: /system.slice/NetworkManager.service
           ├─27815 /usr/sbin/NetworkManager --no-daemon
           └─28306 /sbin/dhclient -d -q -sf /usr/lib/NetworkManager/nm-dhcp-helper -pf /run/dhclient-wlan0.pid -lf /var/lib/NetworkManager/dhclient-da5a19b4-2088-49ae-990d-6461897ba47

6月 01 15:37:32 jetson NetworkManager[27815]: <info>  [1622533052.2892] dhcp4 (wlan0): state changed unknown -> bound
6月 01 15:37:32 jetson NetworkManager[27815]: <info>  [1622533052.2964] device (wlan0): state change: ip-config -> ip-check (reason 'none', sys-iface-state: 'managed')
6月 01 15:37:32 jetson NetworkManager[27815]: <info>  [1622533052.2976] device (wlan0): state change: ip-check -> secondaries (reason 'none', sys-iface-state: 'managed')
6月 01 15:37:32 jetson NetworkManager[27815]: <info>  [1622533052.2983] device (wlan0): state change: secondaries -> activated (reason 'none', sys-iface-state: 'managed')
6月 01 15:37:32 jetson dhclient[28306]: bound to 192.168.0.111 -- renewal in 1515 seconds.
6月 01 15:37:32 jetson NetworkManager[27815]: <info>  [1622533052.3265] device (wlan0): Activation: successful, device activated.
6月 01 15:37:32 jetson NetworkManager[27815]: <info>  [1622533052.3270] manager: startup complete
6月 01 15:37:32 jetson NetworkManager[27815]: <warn>  [1622533052.3288] dns-sd-resolved[0x5596424de0]: Failed: GDBus.Error:org.freedesktop.resolve1.LinkBusy: Link eth0 is managed.
6月 01 15:37:32 jetson NetworkManager[27815]: <warn>  [1622533052.3289] dns-sd-resolved[0x5596424de0]: Failed: GDBus.Error:org.freedesktop.resolve1.LinkBusy: Link eth0 is managed.
6月 01 15:37:32 jetson NetworkManager[27815]: <warn>  [1622533052.3299] dns-sd-resolved[0x5596424de0]: Failed: GDBus.Error:org.freedesktop.resolve1.LinkBusy: Link eth0 is managed.

但是服务无法激活:
```
systemctl enable NetworkManager
```

显示服务已经被屏蔽:

Failed to enable unit: Unit file /etc/systemd/system/NetworkManager.service is masked.

Systemd Service Mask原因¶

systemd服务的所谓 mask 状态，实际上是 disable 的强化版本。当设置服务 disable 时，所有服务单元的软链接都被移除，但是如果配置成 mask 则单元被链接到 /dev/null

通过以下命令检查unit文件状态:
```
systemctl list-unit-files
```

可以看到:

...
NetworkManager-dispatcher.service          disabled
NetworkManager-wait-online.service         disabled
NetworkManager.service                     masked
...

检查unit，可以看到被软链接到 /dev/null

ls -lh /etc/systemd/system/NetworkManager.service

显示:

lrwxrwxrwx 1 root root 9 6月   1 16:22 /etc/systemd/system/NetworkManager.service -> /dev/null

注意到我采用了 Systemd Networkd服务管理了 eth0 ，这导致两者存在冲突。所以关闭掉 systemd-networkd 之后再重新激活 NetworkManager
```
systemctl stop systemd-networkd
systemctl disable systemd-networkd
```

恢复被Mask的服务¶

systemdctl提供了一个 unmask 命令可以去除Mask:
```
systemctl unmask NetworkManger
```

提示信息:

Removed /etc/systemd/system/NetworkManager.service.

然后可以enable该服务:
```
systemctl enable NetworkManager
```

显示:

Created symlink /etc/systemd/system/multi-user.target.wants/NetworkManager.service → /lib/systemd/system/NetworkManager.service.
Created symlink /etc/systemd/system/dbus-org.freedesktop.nm-dispatcher.service → /lib/systemd/system/NetworkManager-dispatcher.service.

启动了NetworkManager之后，可以看到 nmcli conn 显示其管理的网络连接:
```
nmcli conn
```

显示管理了无线，也管理了docker0的bridge网络:

NAME                UUID                                  TYPE      DEVICE
Wired connection 1  a94fa1de-b290-3b83-9f49-137981396543  ethernet  eth0
docker0             0bdc7a88-3f72-438e-9674-0af8fc1af7db  bridge    docker0
office              da5a19b4-2088-49ae-990d-6461897ba471  wifi      wlan0

备注

这里 docker0 的bridge如果没有启动，会导致docker无法正常工作，影响kubernetes工作。

参考¶

Why are some systemd services in the “masked” state?