Process Management

PID is a unique ID number named and it is assigned by the kernel to every process. PIDs are assigned in order as processes are created.
UID is a user identification number of the person who created it.
The EUID is the ‘effective’ user ID, used to determine what resources and files a process has permission to access at any given moment. In general, the UID and EUID are the same, except for the programs that are setuid.
The GID is the group identification number of a process. The EGID is related to the GID in the same way that the EUID is related to the UID. In short, a process can be a member of many groups at once.