Commands

Useful networking commands

ping

Basic reachability and latency. Use ping to determine whether another system is reachable on your network or the Internet.

❯ ping google.com
PING google.com (142.251.41.174): 56 data bytes
64 bytes from 142.251.41.174: icmp_seq=0 ttl=119 time=13.802 ms
64 bytes from 142.251.41.174: icmp_seq=1 ttl=119 time=10.787 ms
64 bytes from 142.251.41.174: icmp_seq=2 ttl=119 time=11.562 ms
--- google.com ping statistics ---
3 packets transmitted, 3 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 8.294/10.828/13.802/1.624 ms

traceroute

Shows the network path packets take.

dig

The dig command queries DNS for information about domain names and their associated records, such as IP addresses, mail servers, and name servers. It is a valuable tool for diagnosing DNS issues and verifying DNS configurations.

The most important section is the ANSWER SECTION:

Output of dig google.com with the DNS answer section highlighted.

The first column lists the name associated with the returned record.
The second column is the Time to Live (TTL).
The third column shows the query class. In this case, IN stands for Internet.
The fourth column displays the query type. In this case, A stands for an A (address) record.
The final column displays the IP address associated with the domain name.

nslookup

Used for obtaining DNS records. Query an IP address with:

nslookup <IP>

ss

The ss command is a simpler and faster alternative to the netstat command.

Output of ss showing socket states, queues, and local and peer addresses.

Common flags

Command	Purpose
`ss -at`	List all TCP connections.
`ss -lt`	List all listening TCP sockets.
`ss -au`	List all UDP sockets.

netstat

netstat shows connections coming to or going from the system, which can help with monitoring and troubleshooting. These notes use ss as its replacement on Linux.

lsof

lsof (LiSt Open Files) is a Linux command that shows open files and the processes accessing them. Every object in Linux, including devices and directories, is treated as a file. This is useful when investigating which process holds a file open.

curl

curl (short for Client URL) is a CLI tool that enables data transfer over various network protocols. It communicates with a web or application server by specifying a relevant URL and the data that needs to be sent or received.

When a URL is provided as an argument, curl outputs the remote content, such as HTML.

Common flags

Flag	Purpose
`curl -O`	Download a file using its remote filename.
`curl -k`	Allow insecure TLS connections by skipping certificate verification.
`curl -i`	Include HTTP response headers in the output.

wget

wget is a free GNU command-line utility used to download files. It retrieves files using HTTP, HTTPS, and FTP and is useful for downloads over unstable networks.

ifconfig

Retrieve information about network interfaces.

ip a

ip a (short for ip address or ip address show) displays IP addresses and network interfaces.

tcpdump

A network sniffer—also called a packet analyzer, protocol analyzer, or network traffic analyzer—can intercept and analyze network traffic that traverses a digital network. tcpdump is a command-line tool for this purpose.

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