User Administration

Type of Users:
Root user                -           Default user highly privileged UID is 0. This will create while installing the operating system
System users         -           is nothing but services, at the time of installing particular package. UID starts from 1 to 499.
Local users            -           after installing of the operating system admin user will create these users. UID starts from 500 to 65534.
Ø  After creating a user, user home directory will be created in default path /home.
Ø  One group is will be created with same user name (primary group)
Ø  Files from /etc/skel will be copied automatically to user home directory
Ø  /etc/passwd file is updated with user information
Ø  /etc/group file is update with primary group information
Important files
/etc/passwd     User Information
/etc/shadow     User Passwords
/etc/group      Group Information
/etc/gshadow    Group Passwords

User Administration Commands:
# useradd <user name>     -           To create specified local user
# useradd –d <home directory> <user name>  - create a user with specified home path

# useradd –u <UID> <user name>         - create user with specific UID.
# passwd <user name>      -           change the user password
# userdel <user name>      -           delete user
# userdel <user name>      -           delete user including home directory
# finger <user name>         -           See user properties
# chfn <user name>            -           Change user information
chfn Command Output
/etc/passwd file user entry

 # chage –l <user name> - to check user password expiry and account expiry information
chage -l Command Output

# su - <user name> -           Switch to other user account
# id <user name>    -           it will show the user id
id Command Output

# system-config-users         -           create and manage user account in GUI

Usermod command options:
-c = We can add comment field for the user account.
-d = To modify the directory for any existing user account.
-e = Using this option we can make the account expiry in specific period.
-g = Change the primary group for a User.
-G = To add a supplementary groups.
-a = To add anyone of the group to a secondary group.
-l = To change the login name
-L = To lock the user account. This will lock the password so we can’t use the account.
-m = moving the contents of the home directory from existing home dir to new dir.
-p = To Use un-encrypted password for the new password. (NOT Secured).
-s = Create a Specified shell for new accounts.
-u = Used to Assigned UID for the user account between 0 to 999.
-U = To unlock the user accounts. This will remove the password lock and allow us to use the user account.

Creating Groups:
Group information is located/stored on /etc/group file.
# groupadd <group name>           - Create a group with specified name
# usermod –G <group name> <user name> - Add user to group
# gpasswd –a ravi Administrators – Adds the user ravi to the group Administrators
# gpasswd –A ravi Administrators – give user ravi administrative rights to the group
# gpasswd –d ravi Administrators – remove user ravi from the group Administrators
# groupdel <group name> - Delete group name
# groupmod –n <new group name> <old group name> - change group name
# newgrp - <group name> - Login into the group if successful, re-initializes the user environment


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