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Linux is most powerful operating system and networking is an essential part of servers. it offers many inbuilt commands to diagnose for network issues. In this article, I will show you useful Linux networking commands, which will help you in troubleshooting.

1. Ifconfig

ifconfig utility is used to configure network interface parameters. Mostly we use this command to check the IP address assigned to the system.

[[email protected] ~]# ifconfig -a

eno16777736: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500

       ether 00:0c:29:c5:a5:61 txqueuelen 1000 (Ethernet)

       RX packets 0 bytes 0 (0.0 B)

       RX errors 0 dropped 0 overruns 0 frame 0

       TX packets 0 bytes 0 (0.0 B)

       TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
 

lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536

       inet 127.0.0.1 netmask 255.0.0.0

       inet6 ::1 prefixlen 128 scopeid 0x10<host>

       loop txqueuelen 0 (Local Loopback)

       RX packets 2 bytes 140 (140.0 B)

       RX errors 0 dropped 0 overruns 0 frame 0

       TX packets 2 bytes 140 (140.0 B)

       TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

[[email protected] ~]#

2. traceroute

traceroute print the route packets take to network host. Destination host or IP is mandatory parameter to use this utility

[[email protected] ~]# traceroute geekflare.com

traceroute to geekflare.com (162.159.243.243), 30 hops max, 60 byte packets

1 172.16.179.2 (172.16.179.2) 0.154 ms 0.074 ms 0.074 ms

2 * * *

3 * * *

3. dig

dig (Domain Information Groper) is a flexible tool for interrogating DNS name servers. It performs DNS lookups and displays the answers that are returned from the name servers.

[[email protected] ~]# dig geekflare.com

; <<>> DiG 9.9.4-RedHat-9.9.4-14.el7 <<>> geekflare.com

;; global options: +cmd

;; Got answer:

;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 18699

;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:

; EDNS: version: 0, flags:; MBZ: 0005 , udp: 4000

;; QUESTION SECTION:

;geekflare.com.                                   IN        A

;; ANSWER SECTION:

geekflare.com.                        5          IN        A          162.159.244.243

geekflare.com.                        5          IN        A          162.159.243.243

;; Query time: 6 msec

;; SERVER: 172.16.179.2#53(172.16.179.2)

;; WHEN: Sun May 01 23:28:19 PDT 2016

;; MSG SIZE rcvd: 74

[[email protected] ~]#

4. telnet

telnet connect destination host:port via a telnet protocol if connection establishes means connectivity between two hosts is working fine.

[[email protected] ~]# telnet geekflare.com 443

Trying 162.159.244.243...

Connected to geekflare.com.

Escape character is '^]'.

5. nslookup

nslookup is a program to query Internet domain name servers.

[[email protected] ~]# nslookup geekflare.com

Server:                        172.16.179.2

Address:         172.16.179.2#53 

Non-authoritative answer:

Name: geekflare.com

Address: 162.159.243.243

Name: geekflare.com

Address: 162.159.244.243

[[email protected] ~]#

6. netstat

netstat command allows you a simple way to review each of your network connections and open sockets. netstat with head output is very helpful while performing web server troubleshooting.

[[email protected] ~]# netstat

Active Internet connections (w/o servers)

Proto Recv-Q Send-Q Local Address           Foreign Address        State    

tcp       0     0 172.16.179.135:58856   mirror.comp.nus.ed:http TIME_WAIT

tcp       0     0 172.16.179.135:34444   riksun.riken.go.jp:http ESTABLISHED

tcp       0     0 172.16.179.135:37948   mirrors.isu.net.sa:http TIME_WAIT

tcp       0     0 172.16.179.135:53128   ossm.utm.my:http       TIME_WAIT

tcp       0     0 172.16.179.135:59723   103.237.168.15:http     TIME_WAIT

tcp       0     0 172.16.179.135:60244   no-ptr.as20860.net:http TIME_WAIT

7. scp

scp allows you to secure copy files to and from another host in the network.

Ex:

scp $filename [email protected]:/$path

8. w

w prints a summary of the current activity on the system, including what each user is doing, and their processes. Also list the logged in users and system load average for the past 1, 5, and 15 minutes.

[[email protected] ~]# w

23:32:48 up 2:52, 2 users, load average: 0.51, 0.36, 0.19

USER     TTY       [email protected] IDLE   JCPU   PCPU WHAT

chandan :0       20:41   ?xdm?   7:07 0.13s gdm-session-worker [pam/gdm-password]

chandan pts/0     20:42   0.00s 0.23s 3.42s /usr/libexec/gnome-terminal-server

[[email protected] ~]#

9. nmap

nmap is a very powerful command, which checks the opened port on the server.

Usage example:

nmap $server_name

10. Enable/Disable Network Interface

You can enable or disable the network interface by using ifup/ifdown commands with ethernet interface parameter.

To enable eth0

#ifup eth0

To disable eth0

#ifdown eth0

I hope above Linux Commands help you to gather network information or troubleshoot the networking issue.

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