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What is User & Group?
What is User?
In Linux, User is the one who uses the system to perform any tasks. Linux has three type of users to access the system.
- Root User: root useralso called as superuser and would have complete access to the system. root account can run any commands without any restriction hence this user called as System Administrator user and its default user created with the Linux installation.
- System User: System Users are those needed for the operation of system-specific components for example mail accounts and the sshd accounts. These System Users are created automatically with the specific software installation to manage the software programs. Usually we should not edit any property of System Users as that would effect the system behaviour.
- Normal User : User Accounts that are created manually to access the system called as Normal Users. Normal Users granted with interactive shell access to type commands to complete certain tasks. Usually Normal Users are created to grant and restrict access to certain files are directories within the Linux System.
TYPE | EXAMPLE | USER ID (UID) | GROUP ID | HOME | SHELL |
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| (GID) | DIRECTORY |
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Super User | Root | 0 | 0 | /root | /bin/bash |
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System User | ftp, ssh, | 1 to 499 | 1 to 499 | /var/ftp, etc... | /sbin/nologin |
| apache |
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| Nobody etc… |
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Normal User | edwiki | 500 to 60000 | 500 to 60000 | /home/username | /bin/bash |
| test etc... |
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Users Attributes:
Whenever a user is created in Linux things created by default:-
- A home directory is created(/home/username)
- A mail box is created(/var/spool/mail)
- unique UID & GID are given to user
Linux uses UPG (User Private Group) scheme
- It means that whenever a user is created is has its own private group
- For Example if a user is created with the name edwiki , then a primary group for that user will be edwiki only
What is Group?
Linux supports creating Group which logically grouping multiple users. Every user must be part of at least one group called as Primary Group.
Linux has two type of Groups:
- Primary Group
- Secondary Group
Groups are useful to manage file or directory permissions effectivey as it allows to grant the permission to set of users who are part of the same Group.
Primary Group:
Every user is part of at least one group as Primary Group. When user creats file or directory then the default group of file or directory is the primary group of the owner.
Secondary Group
Its possible to create groups and assign users to the group. Secondary groups are more useful to grant additional permissions to the user to access files and directories of the same group.
How to see File Properties (Owner, Group, Permissions)
Edwiki#ls -l f1
-rw-r--r-- 1 root root 0 Aug 7 11:36 f1
Edwiki#
How to create user:
How to create group:
How to add users to the group
How to change group of file or directory
-rwxr--r-- 1 root root 0 Jun 27 02:04 f1
[root@ ~]$chgrp oracle f1
[root@ ~]$ls -l f1
-rwxr--r-- 1 root oracle 0 Jun 27 02:04 f1
How to see user groups
uid=1001(iwayq) gid=1001(iwayq) groups=1001(iwayq),1002(oracle)
How to delete user
How to delete group
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