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Finding out which ports are in use

Written by Sebastian De Deyne / Original link on Jul. 9, 2021

Sometimes you want to spin up a process, but the port it wants to bind to is already in use. Or a port isn’t listening to a process as you expected. lsof is a debugging life saver in these situations.

lsof -i -P -n | grep LISTEN

This will list all processes listening to a port.

nginx 514 sebastiandedeyne 7u IPv4 0x2718856ef232ee5b 0t0 TCP 127.0.0.1:80 (LISTEN)
nginx 514 sebastiandedeyne 8u IPv4 0x2718856ef233026b 0t0 TCP 127.0.0.1:443 (LISTEN)
nginx 514 sebastiandedeyne 9u IPv4 0x2718856ef2330c73 0t0 TCP 127.0.0.1:60 (LISTEN)

If you want to find a process on a specific port, you can chain another grep.

lsof -i -P -n | grep LISTEN | grep 80
nginx 514 sebastiandedeyne 7u IPv4 0x2718856ef232ee5b 0t0 TCP 127.0.0.1:80 (LISTEN)

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