I am very new to unix. How can I check that a particular port is free or used right now ?
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unix
netstat -ano|grep 443|grep LISTEN
will tell you whether a process is listening on port 443 (you might have to replace LISTEN with a string in your language, though, depending on your system settings).
Try (maybe as root)
lsof -i -P
and grep the output for the port you are looking for.
For example to check for port 80 do
lsof -i -P | grep :80
Source: Stackoverflow.com