背景
树莓派3B自带一个有线口，一个无线网卡，需要使用有线口上外网，无线连接另一个局域网
试错过程
设置无效
通过等待一分钟删除和添加相关路由的方式无法实现
开机后依然是无线作为出口网卡
sleep 60 && \
route del -net 0.0.0.0/0 gw 172.18.1.254 2>/dev/null && \
route del -net 0.0.0.0/0 gw 172.18.2.254 2>/dev/null && \
route del -net 0.0.0.0/0 gw 172.18.3.254 2>/dev/null && \
route add -net 0.0.0.0/0 gw 172.18.1.254 metric 0 dev eth0 2>/dev/null && \
route del -net 0.0.0.0/0 gw 172.17.1.254 2>/dev/null && \
route del -net 0.0.0.0/0 gw 172.17.2.254
对应帖子是 /p/5d07d46cd434
正确方式
在/etc/network/interfaces设置有线网卡静态IP和网关，无线网卡自动获取IP地址即可，重启多次树莓派都满足需求。
pi@oldpi:~ $ sudo cat /etc/network/interfaces
# interfaces(5) file used by ifup(8) and ifdown(8)
# Please note that this file is written to be used with dhcpcd
# For static IP, consult /etc/ and 'man '
# Include files from /etc/network/:
source-directory /etc/network/
auto eth0
allow-hotplug eth0
#iface eth0 inet dhcp
iface eth0 inet static
address 172.18.1.100
netmask 255.255.255.0
gateway 172.18.1.254
auto eth1
allow-hotplug eth1
iface eth1 inet dhcp
auto eth2
allow-hotplug eth2
iface eth2 inet dhcp
auto wlan0
allow-hotplug wlan0
iface wlan0 inet dhcp
wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf
有多个有线网卡的我还没有测试过，不过理论上可以的。
路由设置也正常，如下，
pi@oldpi:~ $ route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 172.18.1.254 0.0.0.0 UG 0 0 0 eth0
172.18.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
172.17.1.0 0.0.0.0 255.255.255.0 U 0 0 0 wlan0
pi@oldpi:~ $
pi@oldpi:~ $
pi@oldpi:~ $ date
Tue, 02 Nov 2021 09:13:48 +0800