Determine whether the network cable is plugged into the computer

Tool ethtool

If not, sudo apt-Get install ethtool

Run sudo ethtool eth0 on the terminal

Result 1: (when the network cable is inserted)

P {margin-bottom: 0.08in ;}

Supported
Ports: [tp mii]

Supported
Link modes: 10 BaseT/half 10 BaseT/full

100 Baset/half 100 Baset/full

1000 Baset/half 1000 Baset/full

Supports
Auto-negotiation: Yes

Advertised
Link modes: 10 BaseT/half 10 BaseT/full

100 Baset/half 100 Baset/full

1000 Baset/half 1000 Baset/full

Advertised
Pause frame use: No

Advertised
Auto-negotiation: Yes

Link
Partner advertised link modes: 10 BaseT/half 10 BaseT/full

100 Baset/half 100 Baset/full

Link
Partner advertised pause frame use: No

Link
Partner advertised auto-negotiation: Yes

Speed:
100 Mb/s

Duplex:
Full

Port:
MII

Phyad:
0

Transceiver:
Internal

Auto-negotiation:
On

Supports
Wake-on: pumbg

Wake-on:
G

Current
Message Level: Zero X 00000033 (51)

Link
Detected: Yes

Result 2 ):

P {margin-bottom: 0.08in ;}

Supported
Ports: [tp mii]

Supported
Link modes: 10 BaseT/half 10 BaseT/full

100 Baset/half 100 Baset/full

1000 Baset/half 1000 Baset/full

Supports
Auto-negotiation: Yes

Advertised
Link modes: 10 BaseT/half 10 BaseT/full

100 Baset/half 100 Baset/full

1000 Baset/half 1000 Baset/full

Advertised
Pause frame use: No

Advertised
Auto-negotiation: Yes

Link
Partner advertised link modes: not reported

Link
Partner advertised pause frame use: No

Link
Partner advertised auto-negotiation: No

Speed:
10 Mb/s

Duplex:
Half

Port:
MII

Phyad:
0

Transceiver:
Internal

Auto-negotiation:
On

Supports
Wake-on: pumbg

Wake-on:
G

Current
Message Level: Zero X 00000033 (51)

Link
Detected: No

The result of grep "link detected: yes" can be used to determine whether to insert a network cable.

Write the following code in shell:

Ethtool eth0 | grep "link detected: yes"
Check the output of the above command to see if the network cable is connected.
If the output above is empty, the network cable is not connected.
Else network cable connection is normal.