On 1/16/26 5:01 PM, Randall Rose wrote:
Of course, if you can recommend a way of finding out which of the thousands of
packages that currently are or might later be on my machine could be listening
to the network, I would appreciate hearing. That would be useful information.
I just don't know it.
My approach is to do a port scan of myself, to check what network ports
are open and listening for incoming connections using "nmap", pretty
standard program.
First, find out what your network address, say it is 10.1.2.3, then run
something like:
nmap -A -T3 10.1.2.3
When I run it against my laptop I get:
root@theseion:/home/kentborg# nmap -A -T3 10.0.0.184
Starting Nmap 7.95 ( https://nmap.org ) at 2026-01-16 19:06 PST
Nmap scan report for theseion.lan (10.0.0.184)
Host is up (0.000058s latency).
All 1000 scanned ports on theseion.lan (10.0.0.184) are in ignored states.
Not shown: 1000 closed tcp ports (reset)
Too many fingerprints match this host to give specific OS details
Network Distance: 0 hops
OS and Service detection performed. Please report any incorrect
results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 1.72 seconds
root@theseion:/home/kentborg#
Nothing listening, very boring.
Note that if you do an nmap of "localhost" you will see what is visible
from within the machine looking at itself, and can get different
answers, you need to specify your IP address to get what others see.
Even then it is probably cleaner to do the nmap from a different machine
to really get the outside world's perspective.
When I run at against one of my e-mail servers, much more interesting.
I won't paste in the whole output, but I see something is listening on:
- port 22 sshd, good, I use that everyday
- port 25 smtpd, good, needed for incoming e-mail
- port 145 imapd, good, for users to read e-mail
- port 465 ssl/smtp, good, also for users to send e-mail
- port 993 imapd, good, for users to read e-mail, maybe I don't need both.
That's it.
When I do a scan of my web server I see:
- port 22 sshd again
- port 25 smtpd again, though it accepts mail for almost nothing
- port 80 web
- port 443 encrypted web
Again, just what I expect.
If I were to put on a firewall I would have to let those through, and I
would block attempts to talk to…all the other possible ports, that
nothing is listening to anyway.
-kb
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