useful command of the day - testing network connections with ss
When trying to debug your network connection, it is important use sudo dmesg, lspci, and modprobe to see what is happening with problem hardware. But the networking has its own tools for testing the IP stat. It was netstat, but that has been updated to the 'ss' command for several years.
Here is a basic rundown on the ss command:
https://www.howtogeek.com/681468/how-to-use-the-ss-command-on-linux/
It will monitor processes that are attached to network addresses, foreign and local to the system, alive or in a listening state.
For example
flatbush:[ruben]:~$ ss -telwpn
Netid State Recv-Q Send-Q Local Address:Port Peer Address:Port Process
raw UNCONN 2880 0 0.0.0.0:17 0.0.0.0:*
raw UNCONN 3200 0 *:17 *:*
raw UNCONN 0 0 *:58 *:*
raw UNCONN 0 0 *:58 *:*
tcp LISTEN 0 0 0.0.0.0:6514 0.0.0.0:* ino:44776977 sk:a52b0fd9
tcp LISTEN 0 0 0.0.0.0:22 0.0.0.0:* ino:6001 sk:ebca3dc6
tcp LISTEN 0 0 0.0.0.0:514 0.0.0.0:* ino:44776975 sk:5a5b5f2d
tcp LISTEN 0 0 0.0.0.0:601 0.0.0.0:* ino:44776978 sk:aa21acff
tcp LISTEN 0 0 0.0.0.0:631 0.0.0.0:* ino:8233 sk:c50218c6
tcp LISTEN 0 0 127.0.0.1:9000 0.0.0.0:* users:(("ssh",pid=24895,fd=5)) uid:1000 ino:42707633 sk:ac53062e
tcp LISTEN 0 0 [::1]:9000 *:* users:(("ssh",pid=24895,fd=4)) uid:1000 ino:42707632 sk:bc2622bf
tcp LISTEN 0 0 *:22 *:* ino:6003 sk:ed47a438
tcp LISTEN 0 0 *:631 *:* ino:8234 sk:f957dabf
flatbush:[ruben]:~$
This give an extensive listing of processes that are listing on tcp and which ports and process numbers.
This allows one to use other tools to further test networking like netcat
https://linuxize.com/post/netcat-nc-command-with-examples/
or nmap and tcpdump are needed.
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