The sys admin's daily grind: socket statistics
Short Cut
Most sys admins use netstat to find out about the status of network sockets, but Charly knows a good shortcut.
A bunch of parameters control the behavior of netstat. Administrators can also happily combine options so that some netstat calls look like an armadillo has rolled across the keyboard. With ss (like socket statistics), there is an even more specific tool for this purpose. It comes from the iproute2 package [1] – just like its siblings bridge, rtacct, rtmon, tc, ctstat, lnstat, nstat, routef, routel, rtstat, and ip.
Because a running Linux uses several hundred or more ports, ss comes with plenty of filters. I mostly need the -t and -u parameters, which restrict the results to TCP or UDP sockets. Other parameters limit the list to raw, Datagram Congestion Control Protocol (DCCP), package, and Unix domain sockets.
Caution: The tool only displays TCP sockets for existing connections by default (established or close_wait). If I also want to see sockets in the lists status – as I usually do – I have to type ss -ta. If I only want the tool to pay attention to listening TCP sockets and suppress all others, I use ss -lt. If I add -p here, I can also see which process opened the socket. I need to use root privileges for this; otherwise, -p has no effect.
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