Run route command
route -n
Output:
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
10.0.42.0 0.0.0.0 255.255.254.0 U 1 0 0 eth0
169.254.0.0 0.0.0.0 255.255.0.0 U 1000 0 0 eth0
0.0.0.0 10.0.43.254 0.0.0.0 UG 0 0 0 eth0
10.0.43.254 is gateway IP address for the computer. The flag U indicates that route is up and G indicates gateway.
You can also run netstat command to find the gateway.
netstat -nr
Output:
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
10.0.42.0 0.0.0.0 255.255.254.0 U 0 0 0 eth0
169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth0
0.0.0.0 10.0.43.254 0.0.0.0 UG 0 0 0 eth0