Process properties

Each process is a five-digit identifier process ID (PID), and it represents the process for all its life cycle. This means that there cannot be two processes with the same PID at the same time. Their uniqueness makes it possible to access a specific process by knowing its PID. Once a process is terminated, its PID can be reused for another process, if necessary.

Similar to PID, there are other properties that characterize a process. These are as follows:

• PPID: The parent process ID of the process that started this process
• Nice number: Degree of friendliness of this process toward other processes
• Terminal or TTY: Terminal to which the process is connected
• RUID/EUID: The real/effective user ID, which belongs to the owner of the process
• RGID/EGID: The real/effective group owner, the group owner of a process

To see a list of the active processes, there's the ps (process status) command, which shows the current list of running processes for the active user:

> ps -f
UID    PID  PPID  C  STIME  TTY    TIME      CMD
user   8    4     0  Nov03  pts/0  00:00:00  bash -l -i
user   43   8     0  08:53  pts/0  00:00:00  ps -f