[Ubuntu内核18.04.4 5.4 arm64]
我使用 USB 网卡（udev重命名为usb0）。如果启动时连接 UTP 电缆，则没有问题。在这种情况下，我可以拔掉 UTP，然后重新插入。它工作顺利。
如果在启动时拔掉电缆，则热插拔将无法工作。为了解决这个问题，我安装了ifplugd，但它工作不稳定。当我检查每个场景中的服务状态时，我得到：
场景 1-ifplugd服务不适用于usb0：
# service ifplugd status
● ifplugd.service - LSB: Brings up/down network automatically
Loaded: loaded (/etc/init.d/ifplugd; generated)
Active: active (exited) since Mon 2020-09-21 16:43:02 UTC; 20s ago
Docs: man:systemd-sysv-generator(8)
Process: 893 ExecStart=/etc/init.d/ifplugd start (code=exited, status=0/SUCCESS)
Sep 21 16:43:02 umbrela-bridge systemd[1]: Starting LSB: Brings up/down network automatically...
Sep 21 16:43:03 umbrela-bridge ifplugd[893]: * Network Interface Plugging Daemon...
Sep 21 16:43:03 umbrela-bridge ifplugd[893]: * skip usb0...
Sep 21 16:43:03 umbrela-bridge ifplugd[893]: ...done.
Sep 21 16:43:02 umbrela-bridge systemd[1]: Started LSB: Brings up/down network automatically.
root@umbrela-bridge:/home/umbrela#
场景 2-ifplugd服务工作于usb0：
# service ifplugd status
● ifplugd.service - LSB: Brings up/down network automatically
Loaded: loaded (/etc/init.d/ifplugd; generated)
Active: active (running) since Mon 2020-09-21 16:46:26 UTC; 1min 55s ago
Docs: man:systemd-sysv-generator(8)
Process: 884 ExecStart=/etc/init.d/ifplugd start (code=exited, status=0/SUCCESS)
Tasks: 1 (limit: 2291)
CGroup: /system.slice/ifplugd.service
└─912 /usr/sbin/ifplugd -i usb0 -q -f -u0 -d10 -w -I
Sep 21 16:46:25 umbrela-bridge systemd[1]: Starting LSB: Brings up/down network automatically...
Sep 21 16:46:26 umbrela-bridge ifplugd[884]: * Network Interface Plugging Daemon...
Sep 21 16:46:26 umbrela-bridge ifplugd[884]: * start usb0...
Sep 21 16:46:26 umbrela-bridge ifplugd(usb0)[912]: ifplugd 0.28 initializing.
Sep 21 16:46:26 umbrela-bridge ifplugd(usb0)[912]: Using interface usb0/00:0E:C6:00:01:01 with driver <ax
Sep 21 16:46:26 umbrela-bridge ifplugd(usb0)[912]: Using detection mode: SIOCETHTOOL
Sep 21 16:46:26 umbrela-bridge ifplugd(usb0)[912]: Initialization complete, link beat not detected.
Sep 21 16:46:26 umbrela-bridge ifplugd[884]: ...done.
Sep 21 16:46:26 umbrela-bridge systemd[1]: Started LSB: Brings up/down network automatically.
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