Linux 如果不是从 DHCP 获取的，则设置静态 ip（脚本）
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Set static ip if not obtained from DHCP (script)
提问by Bartlomiej Grzeskowiak
I work on embedded device with linux on it. I want to use DHCP client first, but if there will be no answer from DHCP Server I want to set static-default IP. I suppose it shouldn't be complicated, but I haven't found strict answer.
我在带有 linux 的嵌入式设备上工作。我想先使用 DHCP 客户端，但如果 DHCP 服务器没有响应，我想设置静态默认 IP。我想它不应该很复杂，但我还没有找到严格的答案。
I'm thinking about 2 solutions (Unfortunately I can test them in few days):
我正在考虑 2 个解决方案（不幸的是我可以在几天内测试它们）：
I set static IP with ifconfig, then I call udhcpc. If udhcpc will not obtain new IP, old one will stay.
I can also first call udhcpc, wait a while and check if IP is obtained. But this is not nice for me. I wouldn't like to add any wait routines into startup.
我使用 ifconfig 设置静态 IP，然后调用 udhcpc。如果 udhcpc 不会获得新 IP，则旧 IP 将保留。
我也可以先调用udhcpc，稍等片刻，查看是否获取到IP。但这对我来说并不好。我不想在启动中添加任何等待例程。
BR Bartek
BR巴特克
I use udhcpc - something like:
我使用 udhcpc - 类似于：
udhcpc -n -f -i eth0
if ifconfig | grep -A1 eth0 | grep inet
then
采纳答案by Maurizio Lo Bosco
dhclient should support fallback via lease declaration
have a look at the dhclient.confman page.
dhclient 应该通过租约声明支持回退，请查看dhclient.conf手册页。
Add something like this to your dhclient.conf
将这样的内容添加到您的 dhclient.conf
timeout 10;
lease {
interface "eth0";
fixed-address 10.0.0.10;
option subnet-mask 255.255.255.0;
renew 2 2022/1/1 00:00:01;
rebind 2 2022/1/1 00:00:01;
expire 2 2022/1/1 0:00:01;
}
or you can assign a second IP to the interface like /etc/network/interfaces
或者您可以为接口分配第二个 IP，例如 /etc/network/interfaces
auto lo
iface lo inet loopback
iface eth0 inet dhcp
auto eth0:1
iface eth0:1 inet static
address 10.10.10.2
netmask 255.255.255.0
回答by Angelo Babudro
Although an old question, it might be worth noting here that Gentoo Linux has had this functionality for a long time (I've been using it since 2004). Gentoo's network config file (/etc/conf.d/net) allows for fallback IP addresses to be easily specified for any interface in the event that DHCP fails, e.g.:
虽然是一个老问题，但在这里可能值得注意的是，Gentoo Linux 已经有这个功能很长时间了（我从 2004 年开始使用它）。Gentoo 的网络配置文件 (/etc/conf.d/net) 允许在 DHCP 失败的情况下为任何接口轻松指定后备 IP 地址，例如：
modules="dhclient"
config_eth0="dhcp"
config_eth1="dhcp"
dhclient_eth1="nogateway"
fallback_eth0="apipa"
fallback_eth1="192.168.10.10/24"
fallback_routes_eth1="default via 192.168.10.1"
The solution Maurizio provided to use an alias like eth0:0 is fine in many (probably most) situations, but not all. I've run into one piece of software that does not consider eth0:0 to be a suitable substitute for eth0 when it is undefined due to no answer from DHCP, even though it is the same port. So a static fallback address is slightly superior to the alias solution.
Maurizio 提供的使用像 eth0:0 这样的别名的解决方案在许多（可能是大多数）情况下都很好，但不是全部。我遇到了一个软件，它不认为 eth0:0 是 eth0 的合适替代品，因为 eth0 由于没有来自 DHCP 的答复而未定义，即使它是同一个端口。所以静态回退地址略优于别名解决方案。
