I've been trying to modernise my way with Linux by, for one thing, ditching netstat for ss. I looked up my favourite command line flag for netstat in the ss man pages, and was very glad to find that netstat -lnp is more or less the same command as ss -lnp. Or so I thought...

# ss -lnp | grep 1812

Turns up nothing, but

# netstat -lnp | grep 1812
udp        0      0  *                           11103/radiusd

does. A fact that made that particular troubleshooting unnecessarily harder.

Now I'm trying to understand how I should have used ss to verify that the daemon was listening.

Can someone please explain?


# ss --version
ss utility, iproute2-ss090324
# ss -aunp | grep radi
UNCONN     0      0                         *:50482                    *:*      users:(("radiusd",11103,11))
UNCONN     0      0                           *:*      users:(("radiusd",11103,9))
UNCONN     0      0                         *:1812                     *:*      users:(("radiusd",11103,6))
UNCONN     0      0                         *:1813                     *:*      users:(("radiusd",11103,7))
UNCONN     0      0                         *:1814                     *:*      users:(("radiusd",11103,10))
# ss -lnp | grep radi
  • Does radiusd show at all in ss? – derobert Jan 30 '15 at 11:44

A recent version of ss should also display UDP listeners in that way. You can limit to UDP with ss -unlp.

I have tried a recent Debian version where ss --version reports ss utility, iproute2-ss140804 and that does work.

On A Red Hat 5 system with ss utility, iproute2-ss061002 it doesn't. You do get more info there using ss -aunp although that also shows connected ports.

You can also try:

ss -apu state unconnected 'sport = :1812'
  • Odd, none of these commands work on a Raspberry Pi with ss version ss140804. However, they work perfectly on Fedora with ss version ss170501. I guess that's what happens when I use three year old software :( – Navin Dec 2 '17 at 23:45
  • That's why I wrote "A recent version ..." :-) – wurtel Dec 7 '17 at 13:46

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