Courtesy of 3 quick ways to reduce your attack surface on Linux, a command to identify open ports and identify the associated application:
$ ss -tulnp --no-header | awk '{print($1, $5, $7)}'
udp 0.0.0.0:32770 users:(("vlc",pid=2786557,fd=39))
udp 0.0.0.0:32771 users:(("vlc",pid=2786557,fd=40))
udp 127.0.0.1:123
udp 0.0.0.0:123
udp 0.0.0.0:631
udp 0.0.0.0:37019
udp 0.0.0.0:5353
udp 0.0.0.0:39276 users:(("vlc",pid=2786557,fd=50))
udp 0.0.0.0:39277 users:(("vlc",pid=2786557,fd=51))
tcp 0.0.0.0:61209
tcp 127.0.0.1:25
tcp 127.0.0.1:5433
tcp 0.0.0.0:8794
tcp 127.0.0.1:3493
tcp 127.0.0.1:5101 users:(("ssh",pid=899751,fd=4))
tcp 127.0.0.1:5102 users:(("ssh",pid=2187130,fd=4))
tcp 127.0.0.1:5201 users:(("ssh",pid=2186389,fd=5))
tcp 127.0.0.1:5202 users:(("ssh",pid=2186389,fd=7))
tcp 0.0.0.0:22
tcp 127.0.0.1:631
tcp 127.0.0.1:5432
...
