Linux User Management

Creating Users in Linux

Linux allows system administrators to create and manage users with various commands. Below are the key commands used for user management.

1. useradd - Creating a New User

The useradd command is used to create a new user account in Linux.

Basic Syntax:

sudo useradd <username>

Explanation:

• sudo – Runs the command with administrator privileges.
• useradd – The command used to add a new user.
• <username> – Replace with the actual username you want to create.

Example:

sudo useradd yatharth

This will create a new user named yatharth.

2. Setting a Password with passwd

After creating a user, you need to set a password using the passwd command.

Syntax:

sudo passwd <username>

Example:

sudo passwd yatharth

After running this command, the system will prompt you to enter and confirm the new password.

3. id - Display User ID and Group ID

The id command shows the user ID (UID), group ID (GID), and other associated group IDs.

Example:

id yatharth

4. whoami - Display the Current Logged-in User

whoami

5. groups - Show Groups of a User

groups yatharth

6. usermod - Modifying User Accounts

The usermod command allows you to modify user properties like home directory, shell, and group.

Linux User Management

Creating Users in Linux

Linux allows system administrators to create and manage users with various commands. Below are the key commands used for user management.

1. useradd - Creating a New User

The useradd command is used to create a new user account in Linux.

Basic Syntax:

sudo useradd <username>

Explanation:

• sudo – Runs the command with administrator privileges.
• useradd – The command used to add a new user.
• <username> – Replace with the actual username you want to create.

Example:

sudo useradd yatharth

This will create a new user named yatharth.

2. Setting a Password with passwd

After creating a user, you need to set a password using the passwd command.

Syntax:

sudo passwd <username>

Example:

sudo passwd yatharth

After running this command, the system will prompt you to enter and confirm the new password.

3. id - Display User ID and Group ID

The id command shows the user ID (UID), group ID (GID), and other associated group IDs.

Example:

id yatharth

4. whoami - Display the Current Logged-in User

whoami

5. groups - Show Groups of a User

groups yatharth

6. usermod - Modifying User Accounts

The usermod command allows you to modify user properties like home directory, shell, and group.

Change Home Directory:

sudo usermod -d /home/customhome yatharth

This sets /home/customhome as the home directory for yatharth.

Change Username:

sudo usermod -l newyatharth yatharth

This renames yatharth to newyatharth.

Add User to a Group:

sudo usermod -aG sudo yatharth

This adds yatharth to the sudo group (granting administrative privileges).

Assigning Default Directories and User Permissions

1. Default Home Directory

By default, new users get a home directory under /home/<username>. To specify a custom home directory:

sudo useradd -m -d /custom/home yatharth

The -m flag ensures that the directory is created if it doesn’t exist.

2. Setting User Permissions

Linux assigns default file and directory permissions using the chmod and chown commands.

Change File Ownership:

sudo chown yatharth:yatharth /home/yatharth

This assigns ownership of /home/yatharth to the user yatharth.

Change File Permissions:

sudo chmod 700 /home/yatharth

This ensures only yatharth has access to their home directory.

Managing Groups in Linux

1. Show All Groups

getent group

OR

cat /etc/group

2. Show Groups of a Specific User

groups yatharth

OR

id yatharth

3. Create a New Group

sudo groupadd developers

4. Create a Group with a Specific GID

sudo groupadd -g 1050 testers

5. Add a User to a Group

sudo usermod -aG developers yatharth

6. Remove a User from a Group

sudo gpasswd -d yatharth developers

7. Delete a Group

sudo groupdel testers

8. Change a User’s Primary Group

sudo usermod -g developers yatharth

Deleting Users in Linux

To remove users, use the userdel command.

1. Basic User Deletion

sudo userdel yatharth

This deletes the user yatharth but keeps their home directory and files.

2. Delete User and Home Directory

sudo userdel -r yatharth

The -r flag removes the home directory and all user-related files.

3. Remove a User from a Group

sudo gpasswd -d yatharth sudo

This removes yatharth from the sudo group.

Changing Ownership in Linux

Ownership of files and directories can be changed using chown.

1. Change File Ownership

sudo chown yatharth /var/www/html/index.html

This makes yatharth the owner of index.html.

2. Change Group Ownership

sudo chown :developers /var/www/html/index.html

This changes the group ownership to developers.

3. Change Both Owner and Group

sudo chown yatharth:developers /var/www/html/index.html

This assigns yatharth as the owner and developers as the group.

4. View Ownership and Permissions

ls -l /var/www/html/index.html

This displays file ownership and permission details.

Change Home Directory:

sudo usermod -d /home/customhome yatharth

This sets /home/customhome as the home directory for yatharth.

Change Username:

sudo usermod -l newyatharth yatharth

This renames yatharth to newyatharth.

Add User to a Group:

sudo usermod -aG sudo yatharth

This adds yatharth to the sudo group (granting administrative privileges).

Assigning Default Directories and User Permissions

1. Default Home Directory

By default, new users get a home directory under /home/<username>. To specify a custom home directory:

sudo useradd -m -d /custom/home yatharth

The -m flag ensures that the directory is created if it doesn’t exist.

2. Setting User Permissions

Linux assigns default file and directory permissions using the chmod and chown commands.

Change File Ownership:

sudo chown yatharth:yatharth /home/yatharth

This assigns ownership of /home/yatharth to the user yatharth.

Change File Permissions:

sudo chmod 700 /home/yatharth

This ensures only yatharth has access to their home directory.

Deleting Users in Linux

To remove users, use the userdel command.

1. Basic User Deletion

sudo userdel yatharth

This deletes the user yatharth but keeps their home directory and files.

2. Delete User and Home Directory

sudo userdel -r yatharth

The -r flag removes the home directory and all user-related files.

3. Remove a User from a Group

sudo gpasswd -d yatharth sudo

This removes yatharth from the sudo group.

Changing Ownership in Linux

Ownership of files and directories can be changed using chown.

1. Change File Ownership

sudo chown yatharth /var/www/html/index.html

This makes yatharth the owner of index.html.

2. Change Group Ownership

sudo chown :developers /var/www/html/index.html

This changes the group ownership to developers.

3. Change Both Owner and Group

sudo chown yatharth:developers /var/www/html/index.html

This assigns yatharth as the owner and developers as the group.

4. View Ownership and Permissions

ls -l /var/www/html/index.html

This displays file ownership and permission details.