配置网络
配置网络
问题：卡住两分钟
开机启动时出现两分钟的停顿，显示提醒如下：
A start job is running for wait for Network to be configured
然后2分钟超时才能继续启动。
登录之后检查：
$ sudo systemctl status systemd-networkd-wait-online.service
输出为：
$ sudo systemctl status systemd-networkd-wait-online.service
systemd-networkd-wait-online.service - Wait for Network to be Configured
Loaded: loaded (/lib/systemd/system/systemd-networkd-wait-online.service; enabled; vendor preset: enabled)
Active: failed (Result: exit-code) since Sat 2022-01-15 08:12:57 UTC; 7min ago
Docs: man:systemd-networkd-wait-online.service(8)
Process: 1272 ExecStart=/lib/systemd/systemd-networkd-wait-online (code=exited, status=1/FAILURE)
Main PID: 1272 (code=exited, status=1/FAILURE)
Jan 15 08:10:57 skywork2 systemd[1]: Starting Wait for Network to be Configured...
Jan 15 08:11:28 skywork2 systemd-networkd-wait-online[1272]: managing: ens1
Jan 15 08:11:28 skywork2 systemd-networkd-wait-online[1272]: managing: enp6s0
Jan 15 08:11:28 skywork2 systemd-networkd-wait-online[1272]: managing: ens1
Jan 15 08:11:28 skywork2 systemd-networkd-wait-online[1272]: managing: enp6s0
Jan 15 08:12:57 skywork2 systemd-networkd-wait-online[1272]: Event loop failed: Connection timed out
Jan 15 08:12:57 skywork2 systemd[1]: systemd-networkd-wait-online.service: Main process exited, code=exited, status=1/FAILURE
Jan 15 08:12:57 skywork2 systemd[1]: systemd-networkd-wait-online.service: Failed with result 'exit-code'.
Jan 15 08:12:57 skywork2 systemd[1]: Failed to start Wait for Network to be Configured.
问题所在在于网卡的配置：
networkctl
IDX LINK TYPE OPERATIONAL SETUP
1 lo loopback carrier unmanaged
2 enp5s0 ether no-carrier configuring
3 enp6s0 ether routable configured
4 ens1 ether routable configured
5 ibs1d1 infiniband off unmanaged
5 links listed.
解决方案1-减少超时时间
cd /etc/systemd/system/network-online.target.wants/
sudo vi systemd-networkd-wait-online.service
在[Service]下添加一行 TimeoutStartSec=2sec：
[Service]
Type=oneshot
ExecStart=/lib/systemd/systemd-networkd-wait-online
RemainAfterExit=yes
TimeoutStartSec=15sec # 增加这一行
这样15秒钟之后就会继续启动，而不是卡住两分钟，虽然治标不治本。
TBD： 发现我的40G网络会有dhcp获取IP地址很慢的问题，基本要30秒左右才能拿到IP地址，导致启动时很慢。即使这里设置timeout可以继续启动操作系统， 但是进入桌面之后由于40G网络的IP尚未能获取，用40G网络的IP地址会无法访问。千兆网络dhcp的速度就非常快。
解决方案2-配置网络
终极解决方案还是要配置好网络。用 ip 命令查看当前网卡情况：
ip addr
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: enp4s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether 00:e0:4c:68:f7:da brd ff:ff:ff:ff:ff:ff
inet 192.168.0.50/24 brd 192.168.0.255 scope global dynamic enp4s0
valid_lft 81706sec preferred_lft 81706sec
inet6 fe80::2e0:4cff:fe68:f7da/64 scope link
valid_lft forever preferred_lft forever
3: enp5s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN group default qlen 1000
link/ether 00:e0:4c:54:17:3a brd ff:ff:ff:ff:ff:ff
4: enp6s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN group default qlen 1000
link/ether 00:e0:4c:54:17:3b brd ff:ff:ff:ff:ff:ff
5: ens4: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
link/ether 48:0f:cf:ef:08:11 brd ff:ff:ff:ff:ff:ff
inet 10.0.0.50/24 brd 10.0.0.255 scope global dynamic ens4
valid_lft 38533sec preferred_lft 38533sec
inet6 fe80::4a0f:cfff:feef:811/64 scope link
valid_lft forever preferred_lft forever
6: ibs4d1: <BROADCAST,MULTICAST> mtu 4092 qdisc noop state DOWN group default qlen 256
link/infiniband a0:00:03:00:fe:80:00:00:00:00:00:00:48:0f:cf:ff:ff:ef:08:12 brd 00:ff:ff:ff:ff:12:40:1b:ff:ff:00:00:00:00:00:00:ff:ff:ff:ff
参考资料：
但上面的方案对于不准备使用的网口（比如连网线都没插）来说是无效的。对于这样的网口，我们需要彻底的禁用他们。
systemctl | grep net-devices
sys-subsystem-net-devices-enp4s0.device loaded active plugged RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller
sys-subsystem-net-devices-enp5s0.device loaded active plugged RTL810xE PCI Express Fast Ethernet controller
sys-subsystem-net-devices-enp6s0.device loaded active plugged RTL810xE PCI Express Fast Ethernet controller
sys-subsystem-net-devices-ens4.device loaded active plugged MT27520 Family [ConnectX-3 Pro] (InfiniBand FDR/Ethernet 10Gb/40Gb 2-port 544+FLR-QSFP Adapter)
sys-subsystem-net-devices-ibs4d1.device loaded active plugged MT27520 Family [ConnectX-3 Pro] (InfiniBand FDR/Ethernet 10Gb/40Gb 2-port 544+FLR-QSFP Adapter)
实践中发现网上的很多方法都无效，比如 ifconfig / ip 中的 down/up 命令，重启之后就无效了。
目前 systemd 接管的网卡情况如下：
networkctl
$ networkctl
IDX LINK TYPE OPERATIONAL SETUP
1 lo loopback carrier unmanaged
2 enp4s0 ether routable configured
3 enp5s0 ether no-carrier configuring
4 enp6s0 ether no-carrier configuring
5 ens4 ether routable configured
6 ibs4d1 infiniband off unmanaged
在这里，enp5s0 和 enp6s0 这两张网卡是我们希望禁用的。
参考以下资料的说明：
我们在 /usr/lib/systemd/network 目录下放置两个文件来申明我们要禁用两块网卡，操作如下：
cd /usr/lib/systemd/network
sudo vi 01-disable-enp5s0.network
创建文件，内容如下：
[Match]
MACAddress=00:e0:4c:54:17:3a
[Link]
Unmanaged=yes
cd /usr/lib/systemd/network
sudo vi 02-disable-enp6s0.network
创建文件，内容如下：
[Match]
MACAddress=00:e0:4c:54:17:3b
[Link]
Unmanaged=yes
注意：[Match] 这里用 mac 地址来匹配，不要用 name，实际测试中我发现用 name 做匹配和设置 Unmanaged 后，系统中的网卡会发生名字变化的情况，导致匹配出现问题。切记用 mac 地址进行匹配。
重启机器之后，看效果：
$ networkctl
$ networkctl
IDX LINK TYPE OPERATIONAL SETUP
1 lo loopback carrier unmanaged
2 enp4s0 ether routable configured
3 enp5s0 ether off unmanaged # 被禁用了
4 enp6s0 ether off unmanaged # 被禁用了
5 ens4 ether routable configured
6 ibs4d1 infiniband off unmanaged # 这个口本来被禁用了
增加要管理的网卡
有某台机器，出现了网卡状态为 down 的情况，造成无法使用，原因不明。
$ ip addr
......
5: ens4: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
link/ether 70:10:6f:aa:2a:81 brd ff:ff:ff:ff:ff:ff
$ networkctl
IDX LINK TYPE OPERATIONAL SETUP
1 lo loopback carrier unmanaged
2 enp4s0 ether routable configured
3 enp5s0 ether off unmanaged
4 enp6s0 ether off unmanaged
5 ens4 ether off unmanaged
6 ibs4d1 infiniband off unmanaged
解决方法：
cd /usr/lib/systemd/network
vi 03-ens4-dhcp.network
输入以下内容：
[Match]
MACAddress=70:10:6f:aa:2a:81
[Link]
Unmanaged=no
[Network]
DHCP=yes
重启即可。