Script that sets up a different default route for all processes of a particular user on the system

setup-user-route.sh

OTHER_IFACE="eth1"
OTHER_GW="10.0.3.2"
USER="xyz"

ip rule add fwmark 35 table 35
ip route add default via $OTHER_GW dev $OTHER_IFACE table 35
ip route flush cache
iptables -t mangle -A OUTPUT -m owner --uid-owner $USER -j MARK --set-mark 35
iptables -t nat -A POSTROUTING -o $OTHER_IFACE -m mark --mark 35 -j MASQUERADE

Requires the following on OpenWrt/LEDE,

Module for -m owner

# opkg install iptables-mod-extra

For adding a user and running as one,

# opkg install shadow-useradd
# opkg install sudo