Tracking ongoing processes

ps (Process status) can be used to see/list all the running processes. 

$ ps

PID       TTY      TIME        CMD
19        pts/1    00:00:00    sh
24        pts/1    00:00:00    ps

For more information -f (full) can be used along with ps  

$ ps –f

UID      PID  PPID C STIME    TTY        TIME CMD
52471     19     1 0 07:20    pts/1  00:00:00f     sh
52471     25    19 0 08:04    pts/1  00:00:00      ps -f

For single-process information, ps along with process id is used  

$ ps 19

PID       TTY      TIME        CMD
19        pts/1    00:00:00    sh

For a running program (named process) Pidof finds the process id’s (pids) 
Fields described by ps are described as: 

• UID: User ID that this process belongs to (the person running it)
• PID: Process ID
• PPID: Parent process ID (the ID of the process that started it)
• C: CPU utilization of process
• STIME: Process start time
• TTY: Terminal type associated with the process
• TIME: CPU time is taken by the process
• CMD: The command that started this process

There are other options which can be used along with ps command : 

• -a: Shows information about all users
• -x: Shows information about processes without terminals
• -u: Shows additional information like -f option
• -e: Displays extended information

Stopping a process:
When running in foreground, hitting Ctrl + c (interrupt character) will exit the command. For processes running in background kill command can be used if it’s pid is known. 

$ ps –f

UID      PID  PPID C STIME    TTY        TIME CMD
52471     19     1 0 07:20    pts/1  00:00:00      sh
52471     25    19 0 08:04    pts/1  00:00:00      ps –f

$ kill 19
Terminated

If a process ignores a regular kill command, you can use kill -9 followed by the process ID. 

$ kill -9 19
Terminated

A program/command when executed, a special instance is provided by the system to the process. This instance consists of all the services/resources that may be utilized by the process under execution. 

• Whenever a command is issued in Unix/Linux, it creates/starts a new process. For example, pwd when issued which is used to list the current directory location the user is in, a process starts.
• Through a 5 digit ID number Unix/Linux keeps an account of the processes, this number is called process ID or PID. Each process in the system has a unique PID.
• Used up pid’s can be used in again for a newer process since all the possible combinations are used.
• At any point of time, no two processes with the same pid exist in the system because it is the pid that Unix uses to track each process.