Find Unused Unix Ports
Port 443 is already used. Find another free port.
Problem
You need to bring up another Unix web server but port 443 is already in use. How do you find another unused Unix port?
Solution
Use the netstat command to discover which ports are already used
netstat -ln | grep LISTEN | awk '{print $4}' | grep ":" | sort | uniq
Breakdown of commands
netstal -ln : List all the numerical Unix ports that are listening for network traffic
grep LISTEN : Display the output lines that are in LISTEN status
awk '{print $4} : Print the fourth column of the output that has the port numbers that Unix processed are LISTENING
sort | uniq : Sort the output and only show unique values
You will get an output similar to
0.0.0.0:443
0.0.0.0:5353
0.0.0.0:68
0.0.0.0:80
10.0.2.15:123
::1:10089
::1:123
The number after the last colon is the port in use, e.g. 443, 80, 123, 5353. Pick any Unix port not already in use and assigned.
