How to query/change the default gateway via bash on CM12?

Question

When i do a 'busybox route' on CM12 i get this:

localhost / # busybox route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.100.0   *               255.255.255.0   U     0      0        0 wlan0

There is no default gateway defined. Practically there must be one as internet connection works properly (it is also set in Android WiFi settings). Other users seem to have the same routing table behavior (like here). It seems that this behavior started with Android5 as i can see standard "linux style" routing tables (with default gateway) on previous Android versions (like KitKat) on several places on the net.

Anyone know how to query/set/change the default gateway on CM12/Android 5 via shell/bash (not just adding another route with 'route add' - it's more about the specific one that is already set)?

Answer 1

Took me a while to find this answer, so sharing here... Lollipop uses different routing tables with rules per user and/or interface. Here is a sample when I'm connected on wifi:

root@hammerhead:/ # ip rule show
0:      from all lookup local
10000:  from all fwmark 0xc0000/0xd0000 lookup legacy_system
13000:  from all fwmark 0x10063/0x1ffff lookup local_network
13000:  from all fwmark 0x10064/0x1ffff lookup wlan0
14000:  from all oif wlan0 lookup wlan0
15000:  from all fwmark 0x0/0x10000 lookup legacy_system
16000:  from all fwmark 0x0/0x10000 lookup legacy_network
17000:  from all fwmark 0x0/0x10000 lookup local_network
19000:  from all fwmark 0x64/0x1ffff lookup wlan0
22000:  from all fwmark 0x0/0xffff lookup wlan0
23000:  from all fwmark 0x0/0xffff uidrange 0-0 lookup main
32000:  from all unreachable
root@hammerhead:/ # ip route show
# As in your example, there's no default route here
192.168.0.0/24 dev wlan0  proto kernel  scope link  src 192.168.0.42
root@hammerhead:/ # ip route show table wlan0
#But here you find it in the wlan0 table
default via 192.168.0.253 dev wlan0  proto static
192.168.0.0/24 dev wlan0  proto static  scope link

Routing tables are read by priority (the first column in the ip rule show display), using the first match.

You may alter a given routing table by adding 'table table_name' at the end of ip route ... commands.

And thus to get the first available default gateway:

for a in $(ip rule show | grep lookup | sed -r 's/.* lookup ([^ ]+).*/\1/'); do ip route show table $a | grep ^default | cut -d ' ' -f 2-5; done | head -1