Users and Groups in Linux

In Linux, each user is assigned a unique user ID, which is stored in /etc/passwd.

View User Information

To view information about users, you can use the following commands:

cat /etc/passwd          # Display user information from /etc/passwd
id                       # Display the current user's ID
id <USER_NAME>           # Display the ID of a specific user

Adding a New User

To add a new user, you can use the adduser command:

adduser bob              # Creates a new user named 'bob'

Switching Users

To switch to another user, you can use the su (switch user) command:

su bob                   # Switch to the 'bob' account
exit                     # Exit the current user session and return to the previous user or root

Viewing Groups

Groups represent a collection of users. Users can belong to multiple groups. A user’s primary group information is stored in /etc/group.

cat /etc/group           # Display all groups
groups                   # Show the groups the current user belongs to
id                       # Display current user's ID, primary group ID, and group memberships
id bob                   # Display 'bob''s ID, primary group ID, and group memberships

Creating and Modifying Groups

To create a group and add a user to the group, you can use the following commands:

groupadd admin           # Create a group named 'admin'
usermod -a -G admin bob  # Add 'bob' to the 'admin' group
id bob                   # Display 'bob''s ID, primary group ID, and group memberships

To remove a user from a group, you can use the deluser command.

Users

In Linux, each user is assigned a unique user ID. User ID is stored in /etc/passwd.

  cat /etc/passwd

To find a user id, run id command:

  id # returns the current user's id
  id <USER_NAME> # return the user_name's id

to add a new user, use “adduser” command:

adduser bob

to switch to another user use su (switch user) command:

su bob

to exit from a user account, use exit

exit # return back to the prevoius user

Groups

Represent a group of users. You can assign permissions based on groups. A user can belong to multiple groups. A user’s primary group is in /etc/group.

to observe which group a user is belong to:

cat /etc/group # display all groups
groups # show the groupd that current user is belong to
id # shows current user's id, user's primary group id, and users' groups
id bob # shows user's id, user's primary group id, and users' groups

to create a group and add a user to the group:

groupadd admin # create a group admin
usermod -a -G admin bob # add bob to the admin group
id bob # shows user's id, user's primary group id, and users' groups

to remove a user from a group, use ???

# add an example here

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adduser

• Description: Adds a new user to the system.

• Example usage:

  adduser new_user # Creates a new user named 'new_user'
  

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su

• Description: Switches the current user to another user.

• Example usage:

  su new_user # Switches to the 'new_user' account
  exit # Exits the current user session and returns to the previous user or root
  

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deluser

• Description: Removes a user account from the system, along with associated files.

• Example usage:

  deluser newuser # Removes the user account 'newuser'
  

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usermod

• Description: Modifies existing user accounts, changing user properties like username, group membership, or home directory.

• Example usage:

  usermod -aG sudo newuser # Adds 'newuser' to the 'sudo' group
  

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