This is a text-only version of the following page on https://raymii.org:
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Title       :   Get number of incoming connections on specific port with ss
Author      :   Remy van Elst
Date        :   25-08-2020
Last update :   07-11-2020
URL         :   https://raymii.org/s/snippets/Get_number_of_incoming_connections_on_specific_ports_with_ss.html
Format      :   Markdown/HTML
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Recently I had to write a few monitoring plugins, one of which was a count of
incoming established connections to a specific network port. In the  past I
would have used `netstat` and a combination of `grep` and `wc` to filter out only
specific ports and established connections, but nowdays `netstat` is replaced by
`ss` on ubuntu. `ss` has options to filter directly on all sorts of stuff, like
state, ports, protocol, making the command I use more readable and use less
pipes.

Here's an example of the graph my code makes:

![munin ports][2]

[If you like this snippet, consider sponsoring me by trying out a Digital Ocean
VPS. With this link you'll get $100 credit for 60 days). (referral link)][99]




The below snippet is from one of my webservers. You can check the [manpage][1]
for more information, they have another quite elaborate example:

       ss -o state fin-wait-1 '( sport = :http or sport = :https )' dst 193.233.7/24
   List all the tcp sockets in state FIN-WAIT-1 for our apache to network 193.233.7/24
   and look at their timers.

### connection filtering with ss

This is the command, it even works for non-root users, which was nice since my monitoring
plugins do not run as root.

       ss --all --numeric --no-header state established  '( sport = :443 )'

Output:

       tcp                    0                           0                                                 128.199.39.10:443                                           178.200.216.97:55467
       tcp                    0                           0                                                 128.199.39.10:443                                               137.8.9.12:39760
       tcp                    0                           0                                                 128.199.39.10:443                                           213.64.253.119:57065

To count, just add `wc -l`:

       ss --all --numeric --no-header state established  '( sport = :443 )'| wc -l

Output:

       4

Change the port or add more filters, `'( sport = :443 or sport = :80 )'` (mind
the trailing space after the port number), you should be able to figure it out.

## netstat version

On a system that still has `netstat`, I use the following command:

       netstat -anp | grep :443 | grep ESTABLISHED | wc -l

## Long running connections

Update: 2020-11-08

If you want to measure long running connections, a somewhat working example is
the following:

   comm -1 -2 <(ss --all --numeric --no-header state established  '( sport = :443 )' | awk '{print $5}' | awk -F:  'NF{--NF};1' | sort -u) <(sleep 5; ss --all --numeric --no-header state established  '( sport = :443 )' | awk '{print $5}' | awk -F:  'NF{--NF};1' | sort -u) | wc -l

The `comm` command is a reverse `diff` (show all things in common), `-1` and
`-2`. The command executed is the same, only the last command has a `sleep 5`
in front of it:

   ss --all --numeric --no-header state established  '( sport = :443 )' | awk '{print $5}' | awk -F:  'NF{--NF};1' | sort -u

It prints all established connections to port 443, strips out the part after
the last colon (the two awk commands) so that it works with IPv6 as well and
then sort the list, removing duplicates. NATted connections will be counted
once.

This way, you get all IP addresses that have an established connection for at
least 5 seconds in your graph.

I'm using this as a brute force way to measure video live stream viewers.
Regular web requests almost never get into `established`, but these long
running connections do.

[1]: http://manpages.ubuntu.com/manpages/xenial/man8/ss.8.html
[2]: /s/inc/img/munin_port.png


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