Information about services/processes & PID

The compiled commands listed below utilizes a few tools: ps, ss, lsof & pgrep. More details about these tools can be found in the individual pages above.

** TO CONTEMPLATE ABOUT THE COMMANDS WHICH REQUIRES SUDO

Find processes by service name

pgrep flags usage:

• -l: List the process name as well as the process ID

$ pgrep -l <service-name>

# eg. To find PID (Process ID) associated with SSHD (SSH Daesmon)
$ pgrep -l sshd

Retrieve information about a specific PID

ps flags usage:

• -p: To select by PID

$ ps -p <PID> 
$ ps -p <PID> -o pid, cmd # To only display relevant information

Identify the port number related to a PID or service name

Method 1: Using ss

ss flags usage:

• -p: Show processes using sockets

Note: In the example below, the command grep -P ':\d{1,}'essentially uses the Perl regex syntax matching to look for all values with the format of :<1 or more digits> such as :4000, :8000, etc.

$ sudo ss -p | grep <PID> | grep -P ':\d{1,}'

# eg. 
$ sudo ss -p | grep 1400 | grep -P ':\d{1,}'
tcp ESTAB 0    0    
xxxx.xxx.xxx.xxx:4000 xxx.xxx.xxx.xxx:... ....,pid=1400,...

Method 2: Using lsof

lsof flags usage:

• -i: To only list the addresses associated with an internet address (prevent overload of information that are not relevant)

• -P: Prevent conversion of port numbers to port names. For example, listing would appear as :53 instead of :domain

• -n: Prevent conversion of network numbers to host names. For example, listing would appear as 127.0.0.1 instead of localhost

Direct method to look for port numbers relating to a service

$ sudo lsof -i -P -n | grep <service-name>

Look for listening sockets related to a PID or service name

The first portion of the command retrieves all listening sockets.

$ sudo lsof -i -P -n | grep LISTEN

While the second portion narrows the output down to only the specified PID or service name.

$ ... | grep <PID>
$ ... | grep <service-name>

Final command

$ sudo lsof -i -P -n | grep LISTEN | grep <PID>
$ sudo lsof -i -P -n | grep LISTEN | grep <service-name>