User and Group Managment in Linux

To create a new user account under any Linux distribution use command called useradd. The system administrator is responsible for creating account. Login as root user (or use sudo command).

useradd command syntax

useradd [options] {username}
Depending on command line options, the useradd command will update system files (/etc/passwd and /etc/shadow file with password) and may also create the new user's home directory and copy initial files.

Linux add a new user called rakhi

Type the command as follows:
useradd amit
Set a password for rakhi:
passwd amit
Without password user account will be in locked status. To unlock the account, you need to use above passwd command. Use passwd command to assign a password and set password aging guidelines.

Set account disable date

You can set date for the account to be disabled in the format YYYY-MM-DD with -e option while creating account itself:
useradd -e {yyyy-mm-dd} {username}
useradd -e 2008-12-31 jerry

Set default password expiry

The -f {days} option set number of days after the password expires until the account is disabled. (If 0 is specified, the account is disabled immediately after the password expires. If -1 is specified, the account is not be disabled after the password expires.)
useradd -f {days} {username}
useradd -e 2009-12-31 -f 30 jerry

How to create a new group in Linux using groupadd command

 

The groupadd command can be used in Linux to add user groups to the system. The basic syntax of Linux groupadd command is groupadd <groupname>. If no command-line options are used, the group is created with the next available Group ID number (GID) above 499. To specify a GID, use the groupadd -g <gid> <group-name> command.

[root@RHEL2 ~]# groupadd engineering 

Howto: Linux Add User To Group

You can use the useradd or usermod commands to add a user to a group. The useradd command creates a new user or update default new user information. The usermod command modifies a user account i.e. it is useful to add user to existing group. There are two types of group. First is primary user group and other is secondary group. All user account related information is stored in /etc/passwd, /etc/shadow and /etc/group files to store user information.

useradd Example - Add A New User To Secondary Group

You need to the useradd command to add new users to existing group (or create a new group and then add user). If group does not exist, create it. The syntax is as follows:
useradd -G {group-name} username
In this example, create a new user called vivek and add it to group called developers. First login as a root user (make sure group developers exists), enter:
# grep developers /etc/group
Output:

developers:x:1124:

If you do not see any output then you need to add group developers using groupadd command:
# groupadd developers
Next, add a user called vivek to group developers:
# useradd -G developers vivek
Setup password for user vivek:
# passwd vivek
Ensure that user added properly to group developers:
# id vivekOutput:

uid=1122(vivek) gid=1125(vivek) groups=1125(vivek),1124(developers)

Please note that capital G (-G) option add user to a list of supplementary groups. Each group is separated from the next by a comma, with no intervening whitespace. For example, add user jerry to groups admins, ftp, www, and developers, enter:
# useradd -G admins,ftp,www,developers jerry

usermod example - Add a existing user to existing group

Add existing user tony to ftp supplementary/secondary group with usermod command using -a option ~ i.e. add the user to the supplemental group(s). Use only with -G option :
# usermod -a -G ftp tony
Change existing user tony primary group to www:
# usermod -g www tony

Linux: Delete / Remove User Account

You need to use the userdel command to delete a user account and related files from user account. The userdel command must be run as root user. The syntax is as follows:

userdel userName
 

userdel Example

To remove the user vivek account from the local system / server / workstation, enter:
# userdel vivek
To remove the user's home directory pass the -r option to userdel, enter:
# userdel -r vivek
The above command will remove all files along with the home directory itself and the user's mail spool. Please note that files located in other file systems will have to be searched for and deleted manually.

Here are a couple of useful commands that may help you to manipulate users and group in a Linux environment.
Groups are useful when to want multiple users to share some areas among them, while users not in the group won’t have an access to the shared space.
It helps in building a hierarchy in a Linux system.
When you create a new user, a new group is also created with him.

useradd $USER
You can use the command “id” to check the groups of a user.
Here a new user hoge is created.

root@boheme:/etc# id hoge
uid=1003(hoge) gid=1004(hoge) =1004(hoge)
root@boheme:/etc# useradd hoge
root@boheme:/etc# cat /etc/group | grep hoge
hoge:x:1004:

In the case of adding a new user immediately in a primary group, you can use:
useradd -g $GROUP $USER

Here is an example:
root@boheme:/etc# groupadd foo
root@boheme:/etc# useradd -g foo hoge
root@boheme:/etc# id hoge
uid=1003(hoge) gid=1003(foo) =1003(foo)

So here user hoge has been created and has foo as primary group.
You can also add secondary groups to a user, with the option “-G”
usermod -G $GROUP $USER
 
Here is an example:
root@boheme:/etc# groupadd foo2
root@boheme:/etc# usermod -G foo2 hoge
root@boheme:/etc# id hoge
uid=1003(hoge) gid=1003(foo) 所属グループ=1003(foo),1004(foo2)

Here, user hoge has been added to the group foo2, and his primary group has not changed.
You can also remove a use from secondary group with:
 
gpasswd -d $USER $GROUP

How to add and remove groups in Linux

This is one of the key question many new Linux admin faces. The answer is use
groupadd command to create a new group. For example add a new group called sales:

Code:

groupadd sales

To delete a group use groupdel command. For example delete a group called ftpusers:

Code:

groupdel ftpusers