Managing user accounts and groups is a fundamental aspect of system administration, allowing you to control access, privileges, and organizational structure on a computer system. In this guide, we will explore various tasks related to user account creation, group management, password administration, and membership adjustments.

Note: The ones that are highlighted have some explanation.

Tasks

Create user accounts
- Create the user account "alice" with the password "Pass1234" and the home directory "/home/alice."
- Create the user account "bob" with the password "Bob@5678" and the home directory "/home/bob."
- Create a user account with the username "charlie."

Create groups
- Create the group "developers" with Group ID 1010.
- Create the group "designers" with Group ID 1011.

Add user as admin of a group
- Add the user "alice" as the admin of the group "developers."
- Add the user "bob" as the admin of the group "designers."

Create a new password for user
- Create a new password for the user account "alice."

Switch to another user
- Switch to the user account "alice."

Delete user account
- Delete the user account "bob."

Change the login name of user
- Change the login name of the user account "alice" to "alicia."

Add new group
- Add a new group account named "testers."

Delete a group
- Delete the group account "designers."

Add a single user to a group
- Add a single member with the username "charlie" to the group "testers."

Add multiple users to a group
- Add multiple members ("alicia" and "charlie") to the group "developers."

Remove user from a group
- Remove the group member "alicia" from the group "developers."

Solution

Create user accounts
```
 ubuntu@~$: sudo useradd -m alice
 ubuntu@~$: ls /home/
 alice  ubuntu
 ubuntu@~$: sudo passwd alice
 New password: 
 Retype new password: 
 passwd: password updated successfully
 ubuntu@~$: sudo grep alice /etc/passwd
 alice:x:1001:1001::/home/alice:/bin/sh
 ubuntu@~$: sudo grep alice /etc/shadow
 alice:$y$j9T$H3Af2FpfPo10bANWWWgWU/$au0KFIMfWHz.oekhL.tJtc616vD4KrlMXQOOL75l589:19565:0:99999:7:::

 ubuntu@~$: sudo useradd -m bob
 ubuntu@~$: ls /home/
 alice  bob  ubuntu
 ubuntu@~$: sudo passwd bob
 New password: 
 Retype new password: 
 passwd: password updated successfully
 ubuntu@~$: grep bob /etc/passwd
 bob:x:1002:1002::/home/bob:/bin/sh
 ubuntu@~$: sudo grep bob /etc/shadow
 bob:$y$j9T$JNjgYMHI3S3H1v6UcwU8U.$qeW9qRcPK9ruNSf5/ykvsyz4HCn3cXFLRK741N8gAI6:19565:0:99999:7:::

 ubuntu@~$: sudo useradd charlie
 ubuntu@~$: grep charlie /etc/passwd
 charlie:x:1003:1003::/home/charlie:/bin/sh
```
/etc/passwd file contains the user account details. Each field is separated by :

alice:x:1001:1001::/home/alice:/bin/sh

alice - username

x - denotes that the password is encrypted and present in /etc/shadow file

1001 - user ID

1001 - group ID

/home/alice - user home directory

/bin/sh - default login shell

/etc/shadow file contains the secure user details. Each field is separated by :

alice:$y$j9T$H3Af2FpfPo10bANWWWgWU/$au0KFIMfWHz.oekhL.tJtc616vD4KrlMXQOOL75l589:19565:0:99999:7:::

alice - username

$y$j9T$H3Af2FpfPo10bANWWWgWU/$au0KFIMfWHz.oekhL.tJtc616vD4KrlMXQOOL75l589 - encrypted user password

19565 - The date of the last password change, expressed as the number of days since Jan 1, 1970 (Unix time)

0 - the number of days left before the user is allowed to change her password again. An empty field and a value of 0 mean that there is no minimum password age

99999 - The maximum number of days the password is valid, after that user is forced to change her password again

7 - The number of days before password is to expire that user is warned that his/her password must be changed
Create groups
```
 ubuntu@~$: sudo groupadd -g 1010 developers
 ubuntu@~$: grep developers /etc/group
 developers:x:1010:

 ubuntu@~$: sudo groupadd -g 1011 designers
 ubuntu@~$: grep designers /etc/group
 designers:x:1011:
```
/etc/group file contains the information about groups. Each field is separated by :

developers:x:1010:

developers - group name

x - denotes whether the group has a password and whether is it present in /etc/gshadow file

1010 - group ID

The last field is blank as there are no users that are part of developers group
Add user as admin of a group
```
 ubuntu@~$: sudo gpasswd -A alice developers
 ubuntu@~$: sudo grep developers /etc/gshadow
 developers:!:alice:

 ubuntu@~$: sudo gpasswd -A bob designers 
 ubuntu@~$: sudo grep designers /etc/gshadow
 designers:!:bob:
```
/etc/gshadow file contains secure information about groups. Each field is separated by :

developers:!:alice:

developers - group name

! - group password. If the value of this field is !, then no user is allowed to access the group

alice - group administrator

last field is blank because there are no users that are part of developers group

Also, when a user is made admin of the group, it doesn't mean the user is added to the group. alice is made the admin of developers the group but she is not part of the group.

Create a new password for user

 ubuntu@~$: sudo passwd alice
 New password: 
 Retype new password: 
 passwd: password updated successfully

Switch to another user
```
 ubuntu@~$: su - alice
 Password: 
 $ whoami
 alice
 $ pwd
 /home/alice
 $ exit
 ubuntu@~$: 

 ubuntu@~$: su alice
 Password: 
 $ whoami
 alice
 $ pwd
 /home/ubuntu
 $ exit
 ubuntu@~$:
```
There are two ways to switch to another user.

su - alice changes the current directory to the home directory of the target user i.e. /home/alice

su alice the current directory remains the same as of the previous user i.e. /home/ubuntu

Delete user account

 ubuntu@~$: sudo userdel bob
 ubuntu@~$: grep bob /etc/passwd
 ubuntu@~$:

 ubuntu@~$: sudo usermod -l alicia alice
 ubuntu@~$: grep alicia /etc/passwd
 alicia:x:1001:1001::/home/alice:/bin/sh

Add new group

 ubuntu@~$: sudo groupadd testers
 ubuntu@~$: grep testers /etc/group
 testers:x:1012:

Delete a group

 ubuntu@~$: sudo groupdel designers 
 ubuntu@~$: grep designers /etc/group

Add a single user to a group

ubuntu@~$: sudo usermod -aG testers charlie
ubuntu@~$: grep testers /etc/group
testers:x:1012:charlie

Add multiple users to a group

ubuntu@~$: sudo gpasswd -M alicia,charlie developers
ubuntu@~$: grep developers /etc/group
developers:x:1010:alicia,charlie

Remove user from a group

ubuntu@~$: sudo gpasswd -d alicia developers 
Removing user alicia from group developers

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Linux: User and Group Management

Table of contents

Tasks

Create user accounts

Create groups

Add user as admin of a group

Create a new password for user

Switch to another user

Delete user account

Add new group

Delete a group

Add a single user to a group

Add multiple users to a group

Remove user from a group

Solution

Create user accounts

Create groups

Add user as admin of a group

Create a new password for user

Switch to another user

Delete user account

Add new group

Delete a group

Add a single user to a group

Add multiple users to a group

Remove user from a group

Linux: User and Group Management

Table of contents

Tasks

Create user accounts

Create groups

Add user as admin of a group

Create a new password for user

Switch to another user

Delete user account

Change the login name of user

Add new group

Delete a group

Add a single user to a group

Add multiple users to a group

Remove user from a group

Solution

Create user accounts

Create groups

Add user as admin of a group

Create a new password for user

Switch to another user

Delete user account

Change the login name of user

Add new group

Delete a group

Add a single user to a group

Add multiple users to a group

Remove user from a group