ss: another way to get socket statistics

In my last blog post I mentioned ss, another tool that comes with the iproute2 package and allows you to query statistics about sockets. The same thing that can be done with netstat, with the added benefit that it is typically a little bit faster, and shorter to type.

Just ss by default will display much the same thing as netstat, and can be similarly passed options to limit the output to just what you want. For instance:

$ ss -t
State       Recv-Q Send-Q       Local Address:Port                        Peer Address:Port              
ESTAB       0      0                127.0.0.1:postgresql                     127.0.0.1:48154              
ESTAB       0      0            192.168.0.136:35296                      192.168.0.120:8009                
ESTAB       0      0            192.168.0.136:47574                     173.194.74.189:https

[...]

ss -t shows just TCP connections. ss -u can be used to show UDP connections, -l will show only listening ports, and things can be further filtered to just the information you want.

I have not tested all the possible options, but you can even forcibly close sockets with -K.

One place where ss really shines though is in its filtering capabilities. Let's list all connections with a source port of 22 (ssh):

$ ss state all sport = :ssh
Netid State      Recv-Q Send-Q     Local Address:Port                      Peer Address:Port              
tcp   LISTEN     0      128                    *:ssh                                  *:*                  
tcp   ESTAB      0      0          192.168.0.136:ssh                      192.168.0.102:46540              
tcp   LISTEN     0      128                   :::ssh                                 :::* 

And if I want to show only connected sockets (everything but listening or closed):

$ ss state connected sport = :ssh
Netid State      Recv-Q Send-Q     Local Address:Port                      Peer Address:Port              
tcp   ESTAB      0      0          192.168.0.136:ssh                      192.168.0.102:46540 

Similarly, you can have it list all connections to a specific host or range; in this case, using the 74.125.0.0/16 subnet, which apparently belongs to Google:

$ ss state all dst 74.125.0.0/16
Netid State      Recv-Q Send-Q     Local Address:Port                      Peer Address:Port              
tcp   ESTAB      0      0          192.168.0.136:33616                   74.125.142.189:https              
tcp   ESTAB      0      0          192.168.0.136:42034                    74.125.70.189:https              
tcp   ESTAB      0      0          192.168.0.136:57408                   74.125.202.189:https        

This is very much the same syntax as for iptables, so if you're familiar with that already, it will be quite easy to pick up. You can also install the iproute2-doc package, and look in /usr/share/doc/iproute2-doc/ss.html for the full documentation.

Try it for yourself! You'll see how well it works. If anything, I'm glad for the fewer characters this makes me type.