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Linux OS provides multiple user environment, so more than one users can work simultaneously. User account management is the process of organizing user accounts.Its necessory in a multiuser environment.
User management
Show all built-In Users
View the file /etc/passwd to know the list of all user accounts in the OS.
[root@server ~#]cat /etc/passwd
(from the output of the above command , you can view all the users and groups, their home directory, user id, group id, default shell, etc.)
[root@server ~#]id (displays userid and group id of currently logged in user)
[root@server ~#]id james -g -n (displays primary group id of user james)
Other parameters can be used with "id" command:
Parameter Description.
-g Dispalys primary group id
-G Displays all group id(s) with which the user linked
-n Displays the name of the user
-u Displays the user id of the specified user
Adding a Linux User
the command "useradd" is used for creating a linux user, More parameters can be used with this command.
[root@server ~#]useradd james (this command create a user with username james)
Some useful parameters can be used with useradd command
Parameter Description.
-c Add a description about the user
-d Specify the home directory of user
-e Define expiry date of user account
-f Specify the days which the user account remains active after password expiry
-g Specify the primary groupof user account
-G Specify the supplementary groups
-M Ensure that user's home directory is not created
-p Specify encrypted password
-s specify the default shell of user
-n specify user id
Usage:[root@server ~#] useradd -s /sbin/nologin james (create user with nologin shell)
Modifying Linux User Account
Use "usermod" command to modify a linuc user account
Available Parameters
Parameter Description.
-c Modify description of user account
-d Modify home directory (use -m parameter to copy the files in old home folder to new home folder)
-e Modify account expiry date
-f Modify the days which the user account remains active after password expiry
-g Modify the primary group
-G Modify the supplementary groups
-p Modify encrypted password
-s Modify default shell
-l Modify the login name of an existing user account
-u Modify a user-id of a user account
-L Lock an existing user account
-U Unlock a locked user account
Eg: [root@server ~#]usermod -c "Accounting section" -s /sbin/nologin acc
(Here the account acc's desctiption and default shell is modified)
Deleting a user account
[root@server ~#]userdel james (home directory of user will not deleted)
[root@server ~#]userdel -r james (Home directory will be removed)
(userdel cannot delete a user account if that user is currently logged in, So Kill or logout a user )
To kill and logout a user
[root@server ~#]skill -KILL -u james (force logout the user- james)
To STOP/PAUSE a user's activities
[root@server ~#]skill -STOP -u james
To RESUME a stopped user
[root@server ~#]skill -CONT -u james
To kill/logout a user in pts/1 or pts/*
[root@server ~#]skill -KILL -v pts/1
Groups management
View all Groups in OS
[root@server ~#]cat /etc/group
Add a Group
[root@server ~#]groupadd -g 888 guests (create a group named guests with group-id 888)
Modifying Groups
[root@server ~#]groupmod -g 777 -n members guests (rename the group name from guests to members and change the group-id to 777)
Deleting a group
[root@server ~#]groupdel members (Delete a group named "members")
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