as every Linux sys admin know the IP address of the Linux machine we can get as
ifconfig -a|grep inet | awk -F":" '{print $2}' | head -1 | awk '{print $1}'
or
ip addr
or just look the ifcfg files
but how to know the IP from /proc/net/tcp file?
how to understand from the tcp the IP address?
cat /proc/net/tcp
sl local_address rem_address st tx_queue rx_queue tr tm->when retrnsmt uid timeout inode
0: 0100007F:F780 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10501 0 17506 1 efd8e040 3000 0 0 2 -1
1: 0100007F:F781 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10501 0 17508 1 efd8e4c0 3000 0 0 2 -1
2: 00000000:5281 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10501 0 17195 1 efd8f6c0 3000 0 0 2 -1
3: 00000000:02A1 00000000:0000 0A 00000000:00000000 00:00000000 00000000 0 0 8255 1 f69796c0 3000 0 0 2 -1
4: 0100007F:F782 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10501 0 17510 1 f4a6fb40 3000 0 0 2 -1
5: 0100007F:F783 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10501 0 17512 1 f4a6f6c0 3000 0 0 2 -1
6: 79176A0A:13C4 00000000:0000 0A 00000000:00000000 00:00000000 00000000 14201 0 18908 1 f06864c0 3000 0 0 2 -1
7: 0100007F:F784 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10501 0 17514 1 f4a6f240 3000 0 0 2 -1
8: 00000000:D804 00000000:0000 0A 00000000:00000000 00:00000000 00000000 23200 0 12839 1 f64d2040 3000 0 0 2 -1
9: 0100007F:F785 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10501 0 17516 1 f4a6edc0 3000 0 0 2 -1
10: 00000000:D805 00000000:0000 0A 00000000:00000000 00:00000000 00000000 23200 0 13004 1 f6773b40 3000 0 0 2 -1
11: 00000000:1E25 00000000:0000 0A 00000000:00000000 00:00000000 00000000 0 0 9568 1 f760d240 3000 0 0 2 -1
12: 0100007F:F786 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10501 0 17518 1 f4a6e940 3000 0 0 2 -1
13: 0100007F:D806 00000000:0000 0A 00000000:00000000 00:00000000 00000000 23200 0 13121 1 f6773240 3000 0 0 2 -1
14: 0100007F:F787 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10501 0 17520 1 f4a6e4c0 3000 0 0 2 -1
15: 0100007F:00C7 00000000:0000 0A 00000000:00000000 00:00000000 00000000 0 0 8921 1 f69784c0 3000 0 0 2 -1
16: 0100007F:F788 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10501 0 17522 1 f4a6e040 3000 0 0 2 -1
17: 0100007F:F789 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10501 0 17524 1 f1ec1b40 3000 0 0 2 -1
18: 00000000:1389 00000000:0000 0A 00000000:00000000 00:00000000 00000000 23200 0 13090 1 f64d2940 3000 0 0 2 -1
19: 0100007F:F78A 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10501 0 17526 1 f1ec16c0 3000 0 0 2 -1
20: 00000000:1A0A 00000000:0000 0A 00000000:00000000 00:00000000 00000000 0 0 9026 1 f6978040 3000 0 0 2 -1
21: 0100007F:F78B 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10501 0 17528 1 f1ec1240 3000 0 0 2 -1
22: 0100007F:F78C 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10501 0 17530 1 f1ec0dc0 3000 0 0 2 -1
23: 0100007F:F78D 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10501 0 17532 1 f1ec0940 3000 0 0 2 -1
24: 00000000:060E 00000000:0000 0A 00000000:00000000 00:00000000 00000000 14201 0 18877 1 f0686dc0 3000 0 0 2 -1
25: 0100007F:F78E 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10501 0 17534 1 f1ec04c0 3000 0 0 2 -1
26: 00000000:006F 00000000:0000 0A 00000000:00000000 00:00000000 00000000 0 0 8130 1 f6979b40 3000 0 0 2 -1
27: 0100007F:0610 00000000:0000 0A 00000000:00000000 00:00000000 00000000 14201 0 18909 1 f0687240 3000 0 0 2 -1
28: 0100007F:D994 00000000:0000 0A 00000000:00000000 00:00000000 00000000 48 0 14482 1 f64d2dc0 3000 0 0 2 -1
29: 0100007F:0035 00000000:0000 0A 00000000:00000000 00:00000000 00000000 25 0 7961 1 f760db40 3000 0 0 2 -1
30: 00000000:0016 00000000:0000 0A 00000000:00000000 00:00000000 00000000 0 0 8854 1 f6978dc0 3000 0 0 2 -1
31: 00000000:F297 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10101 0 9618 1 f7bd8040 3000 0 0 2 -1
32: 0100007F:03B9 00000000:0000 0A 00000000:00000000 00:00000000 00000000 25 0 7962 1 f760d6c0 3000 0 0 2 -1
33: 0100007F:F77B 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10501 0 17496 1 f0510040 3000 0 0 2 -1
34: 0100007F:F77C 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10501 0 17498 1 f05104c0 3000 0 0 2 -1
35: 0100007F:F77D 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10501 0 17500 1 f0511b40 3000 0 0 2 -1
36: 0100007F:F77E 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10501 0 17502 1 f05116c0 3000 0 0 2 -1
37: 0100007F:F77F 00000000:0000 0A 00000000:00000000 00:00000000 00000000 10501 0 17504 1 f0511240 3000 0 0 2 -1
38: 00000000:D8FF 00000000:0000 0A 00000000:00000000 00:00000000 00000000 23200 0 13023 1 f67736c0 3000 0 0 2 -1
39: 0100007F:041F 00000000:0000 0A 00000000:00000000 00:00000000 00000000 0 0 8920 1 f6978940 3000 0 0 2 -1
40: 79176A0A:0016 7863770A:8C1E 01 00000000:00000000 02:0000473D 00000000 0 0 19488326 2 f363f240 202 40 14 3 100
41: 0100007F:952C 0100007F:060E 06 00000000:00000000 03:00000C08 00000000 0 0 0 2 e96deec0
42: 0100007F:952F 0100007F:060E 06 00000000:00000000 03:000013D9 00000000 0 0 0 2 e96dee40
43: 0100007F:952E 0100007F:060E 06 00000000:00000000 03:00000FF0 00000000 0 0 0 2 e96de8c0
44: 0100007F:952B 0100007F:060E 06 00000000:00000000 03:00000820 00000000 0 0 0 2 e96def40
45: 0100007F:952A 0100007F:060E 06 00000000:00000000 03:00000438 00000000 0 0 0 2 e96deb40
46: 0100007F:D6D4 0100007F:041F 01 00000000:00000000 00:00000000 00000000 10101 0 9610 1 f7bd8940 202 40 30 2 100
47: 0100007F:D6D1 0100007F:041F 01 00000000:00000000 00:00000000 00000000 10101 0 9594 1 f64d3b40 201 40 28 2 100
48: 0100007F:D6D0 0100007F:041F 01 00000000:00000000 00:00000000 00000000 10101 0 9592 1 f760c940 208 40 32 2 100
49: 0100007F:D6D3 0100007F:041F 01 00000000:00000000 00:00000000 00000000 10101 0 9597 1 f7bd9240 201 40 24 2 100
50: 0100007F:D6D2 0100007F:041F 01 00000000:00000000 00:00000000 00000000 10101 0 9596 1 f7bd9b40 201 40 26 2 100
51: 0100007F:D6E5 0100007F:041F 01 00000000:00000000 00:00000000 00000000 10501 0 15008 1 f67724c0 201 40 30 2 100
52: 0100007F:D6E4 0100007F:041F 01 00000000:00000000 00:00000000 00000000 10501 0 14626 1 f64d3240 201 40 30 2 100
53: 0100007F:D6E7 0100007F:041F 01 00000000:00000000 00:00000000 00000000 10501 0 16296 1 f0510dc0 201 40 30 2 100
54: 0100007F:D6F2 0100007F:041F 01 00000000:00000000 00:00000000 00000000 14201 0 18883 1 f0686940 201 40 30 2 100
55: 0100007F:041F 0100007F:D6D4 01 00000000:00000000 00:00000000 00000000 0 0 9611 1 f7bd84c0 201 40 31 2 100
56: 0100007F:041F 0100007F:D6D0 01 00000000:00000000 00:00000000 00000000 0 0 9593 1 f760c040 211 65 33 2 100
57: 0100007F:041F 0100007F:D6D1 01 00000000:00000000 00:00000000 00000000 0 0 9595 1 f64d36c0 212 46 29 2 100
58: 0100007F:041F 0100007F:D6D2 01 00000000:00000000 00:00000000 00000000 0 0 9599 1 f7bd96c0 205 40 27 2 100
59: 0100007F:041F 0100007F:D6D3 01 00000000:00000000 00:00000000 00000000 0 0 9600 1 f7bd8dc0 205 40 25 2 100
60: 0100007F:DB38 0100007F:D804 06 00000000:00000000 03:00000C44 00000000 0 0 0 2 e96de9c0
61: 0100007F:041F 0100007F:D6E4 01 00000000:00000000 00:00000000 00000000 0 0 14627 1 f6772040 201 40 31 2 100
62: 0100007F:041F 0100007F:D6E5 01 00000000:00000000 00:00000000 00000000 0 0 15009 1 f6772940 201 40 31 2 100
63: 0100007F:041F 0100007F:D6E7 01 00000000:00000000 00:00000000 00000000 0 0 16301 1 f0510940 201 40 31 2 100
64: 79176A0A:0016 58326A0A:82EB 01 00001ACC:00000000 01:00000017 00000000 0 0 19529421 4 f6979240 240 62 3 4 100
65: 0100007F:041F 0100007F:D6F2 01 00000000:00000000 00:00000000 00000000 0 0 18884 1 f0687b40 201 40 31 2 100
Each line starts with a hexadecimal form of IPv4 address and port number, with lower byte representing the first part of the address:
0100007F:0016 == 01.00.00.7F:0016 == 127.0.0.1:22
79176A0A:13C4 == 79.17.6A.0A:13C4 == 10.106.23.121:5060
The local IP address and port number for the socket. The IP address is displayed as a little-endian four-byte hexadecimal number; that is, the least significant byte is listed first, so you'll need to reverse the order of the bytes to convert it to an IP address. The port number is a simple two-byte hexadecimal number.