When looking at the operating system one of your best friends will be lsof. lsof stands forlists information about files opened by processes for the following UNIX dialects . As everything under Linux is a file this tool will show you everything you could possible want to know.
Examples how to use “lsof” :
To list all open files:
lsof
To list all open IPv4 network files in use by the process
whose PID is 1234 :
lsof -i 4 -a -p 1234
Presuming the UNIX dialect supports IPv6, to list only open
IPv6 network files :
lsof -i 6
To list all files using any protocol on ports 21 of hostnames:
lsof -i @hostname:portnumbers
To list all files using any protocol on any port of
hostname :
lsof -i @hostname
