For others searching for help,
To connect Beaglebone black to Ubuntu system, via Ethernet cable,
Power up your BeagleBone
Connect the Ethernet cable
run ifconfig on your main system and see the Ethernet port
for example:
$ ifconfig
eth0 Link encap:Ethernet HWaddr 18:03:73:70:d8:fa
inet addr:10.42.0.1 Bcast:10.42.0.255 Mask:255.255.255.0
inet6 addr: fe80::1a03:73ff:fe70:d8fa/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:7547 errors:1 dropped:0 overruns:0 frame:1
TX packets:5126 errors:0 dropped:0 overruns:0 carrier:11
collisions:0 txqueuelen:1000
RX bytes:9630936 (9.6 MB) TX bytes:422695 (422.6 KB)
eth1 Link encap:Ethernet HWaddr 78:a5:04:cd:e7:52
inet6 addr: fe80::7aa5:4ff:fecd:e752/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:52 errors:0 dropped:0 overruns:0 frame:0
TX packets:1125 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:8766 (8.7 KB) TX bytes:272946 (272.9 KB)
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:29792 errors:0 dropped:0 overruns:0 frame:0
TX packets:29792 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:5627707 (5.6 MB) TX bytes:5627707 (5.6 MB)
wlan0 Link encap:Ethernet HWaddr 38:59:f9:5f:69:06
inet addr:192.168.43.79 Bcast:192.168.43.255 Mask:255.255.255.0
inet6 addr: fe80::3a59:f9ff:fe5f:6906/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:111262 errors:0 dropped:0 overruns:0 frame:0
TX packets:121625 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:78921601 (78.9 MB) TX bytes:17154117 (17.1 MB)
So, as you can see the eth0 is connected with ip address 10.42.0.1
We now know that beaglebone would have an ip like 10.42.0.*
I further used nmap scan to find the ip address of beaglebone
as
$ nmap -F 10.42.0.*
Starting Nmap 6.40 ( http://nmap.org ) at 2016-02-19 01:09 IST
Nmap scan report for 10.42.0.1
Host is up (0.0013s latency).
Not shown: 97 closed ports
PORT STATE SERVICE
53/tcp open domain
139/tcp open netbios-ssn
445/tcp open microsoft-ds
Nmap scan report for 10.42.0.79
Host is up (0.0023s latency).
Not shown: 95 closed ports
PORT STATE SERVICE
22/tcp open ssh
80/tcp open http
3000/tcp open ppp
3389/tcp open ms-wbt-server
8080/tcp open http-proxy
Nmap done: 256 IP addresses (2 hosts up) scanned in 3.30 seconds
So, as the nmap result shows, the ip address of beaglebone black is 10.42.0.79 and you can ssh over that ip address.