我正在运行带有 HWE 的 18.04.4 LTS。
重启后，我必须手动运行“sudo netplan apply”来设置 50-cloud-init.yaml 中描述的静态 IP：
network:
ethernets:
renderer: networkd
enp0s25:
dhcp4: no
optional: false
addresses: [172.28.1.99/24]
gateway4: 172.28.1.1
nameservers:
addresses: [172.28.1.99, 172.28.1.1]
version: 2
我看到很多帖子谈论跳过等待网络可用的过程，但没有关于如何强制等待网络的帖子。
因此，登录后，我可以立即应用 netplan，几秒钟后，静态 IP 就应用了，并且卡也启动了。
查看 journalctl --no-pager -lu systemd-networkd，启动期间只有“权限被拒绝”错误......
-- Reboot --
Feb 04 20:10:52 lei systemd[1]: Starting Network Service...
Feb 04 20:10:52 lei systemd-networkd[935]: Failed to connect to bus: Permission denied
Feb 04 20:10:52 lei systemd-networkd[935]: Could not connect to bus: Permission denied
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Main process exited, code=exited, status=1/FAILURE
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Failed with result 'exit-code'.
Feb 04 20:10:52 lei systemd[1]: Failed to start Network Service.
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Service has no hold-off time, scheduling restart.
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Scheduled restart job, restart counter is at 1.
Feb 04 20:10:52 lei systemd[1]: Stopped Network Service.
Feb 04 20:10:52 lei systemd[1]: Starting Network Service...
Feb 04 20:10:52 lei systemd-networkd[936]: Failed to connect to bus: Permission denied
Feb 04 20:10:52 lei systemd-networkd[936]: Could not connect to bus: Permission denied
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Main process exited, code=exited, status=1/FAILURE
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Failed with result 'exit-code'.
Feb 04 20:10:52 lei systemd[1]: Failed to start Network Service.
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Service has no hold-off time, scheduling restart.
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Scheduled restart job, restart counter is at 2.
Feb 04 20:10:52 lei systemd[1]: Stopped Network Service.
Feb 04 20:10:52 lei systemd[1]: Starting Network Service...
Feb 04 20:10:52 lei systemd-networkd[938]: Failed to connect to bus: Permission denied
Feb 04 20:10:52 lei systemd-networkd[938]: Could not connect to bus: Permission denied
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Main process exited, code=exited, status=1/FAILURE
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Failed with result 'exit-code'.
Feb 04 20:10:52 lei systemd[1]: Failed to start Network Service.
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Service has no hold-off time, scheduling restart.
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Scheduled restart job, restart counter is at 3.
Feb 04 20:10:52 lei systemd[1]: Stopped Network Service.
Feb 04 20:10:52 lei systemd[1]: Starting Network Service...
Feb 04 20:10:52 lei systemd-networkd[939]: Failed to connect to bus: Permission denied
Feb 04 20:10:52 lei systemd-networkd[939]: Could not connect to bus: Permission denied
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Main process exited, code=exited, status=1/FAILURE
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Failed with result 'exit-code'.
Feb 04 20:10:52 lei systemd[1]: Failed to start Network Service.
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Service has no hold-off time, scheduling restart.
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Scheduled restart job, restart counter is at 4.
Feb 04 20:10:52 lei systemd[1]: Stopped Network Service.
Feb 04 20:10:52 lei systemd[1]: Starting Network Service...
Feb 04 20:10:52 lei systemd-networkd[940]: Failed to connect to bus: Permission denied
Feb 04 20:10:52 lei systemd-networkd[940]: Could not connect to bus: Permission denied
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Main process exited, code=exited, status=1/FAILURE
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Failed with result 'exit-code'.
Feb 04 20:10:52 lei systemd[1]: Failed to start Network Service.
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Service has no hold-off time, scheduling restart.
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Scheduled restart job, restart counter is at 5.
Feb 04 20:10:52 lei systemd[1]: Stopped Network Service.
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Start request repeated too quickly.
Feb 04 20:10:52 lei systemd[1]: systemd-networkd.service: Failed with result 'exit-code'.
Feb 04 20:10:52 lei systemd[1]: Failed to start Network Service.
然后，当我执行 netplan apply 时的条目......
Feb 04 20:11:49 lei systemd[1]: Starting Network Service...
Feb 04 20:11:49 lei systemd-networkd[2856]: Enumeration completed
Feb 04 20:11:49 lei systemd[1]: Started Network Service.
Feb 04 20:11:49 lei systemd-networkd[2856]: lo: Link is not managed by us
Feb 04 20:11:53 lei systemd-networkd[2856]: enp0s25: Gained carrier
Feb 04 20:11:54 lei systemd-networkd[2856]: enp0s25: Gained IPv6LL
Feb 04 20:11:54 lei systemd-networkd[2856]: enp0s25: Configured
我按照 heynnema 的建议实施了更严格的 .yaml 配置，但结果仍然相同。netplan --debug generate 返回：
root@l:/etc/netplan# netplan --debug generate
DEBUG:command generate: running ['/lib/netplan/generate']
** (generate:22264): DEBUG: 21:54:44.867: Processing input file /etc/netplan/50-cloud-init.yaml..
** (generate:22264): DEBUG: 21:54:44.867: starting new processing pass
** (generate:22264): DEBUG: 21:54:44.868: enp0s25: setting default backend to 1
** (generate:22264): DEBUG: 21:54:44.868: Configuration is valid
** (generate:22264): DEBUG: 21:54:44.868: Generating output files..
** (generate:22264): DEBUG: 21:54:44.868: NetworkManager: definition enp0s25 is not for us (backend 1)
重新启动时，我仍然没有静态 IP，直到我手动执行 netplan apply...
dparks@l:~$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: enp0s25: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
link/ether d0:50:99:67:5e:2b brd ff:ff:ff:ff:ff:ff
dparks@l:~$
dparks@l:~$ sudo netplan apply
[sudo] password for dparks:
dparks@l:~$
dparks@l:~$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: enp0s25: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether d0:50:99:67:5e:2b brd ff:ff:ff:ff:ff:ff
inet 172.28.1.99/24 brd 172.28.1.255 scope global enp0s25
valid_lft forever preferred_lft forever
inet6 fe80::d250:99ff:fe67:5e2b/64 scope link
valid_lft forever preferred_lft forever
/etc/systemd/network 是空的：
dparks@l:~$ ls -al /etc/systemd/network
total 8
drwxr-xr-x 2 root root 4096 Apr 20 2018 .
drwxr-xr-x 5 root root 4096 Feb 6 06:18 ..
该问题被确定为根文件夹的权限问题：
dr-xr-x--x 26 root root 4096 Feb 4 20:09 /
更正为 0755 解决了该问题并且 netplan 在启动时正确应用。
drwxr-xr-x 26 root root 4096 Feb 4 20:09 /