Users and groups in linux

Users

-Every user is assigned a unique User ID number (UID).

-UID 0 identifies root.

-Users' names and UID's are stored in /etc/passwd.

-Users cannot read, write or execute each others' files without permission.

Groups

-Users are assigned to groups.

-Each group is assigned a unique Group ID number (gid).

-GIDs are stored in /etc/group.

Enjoy:-)