Users and groups

ChatGPT

2025-01-27

useradd

Adds a new user to the system. The user will be assigned default values unless further options are specified.

Command Description
useradd <username> Creates a user and their home directory.
useradd -s <shell> <username> Specifies a shell for the user (e.g., /bin/bash).
useradd -g <group> <username> Assigns the user to a specific group.

To check user configuration, open the /etc/passwd file. The file uses a colon : as the delimiter between columns. Each line represents a user and contains the following information in tabular format:

Col Field Name Description
1 Username The login name of the user.
2 Password Often shown as x, indicating the password is stored securely in the shadow file.
3 UID (User ID) A unique numerical identifier assigned to the user.
4 GID (Group ID) The primary group ID for the user, which links to an entry in /etc/group.
5 User Info Optional field for additional user details, such as full name or description.
6 Home Directory The path to the user’s home directory.
7 Shell The default shell assigned to the user (e.g., /bin/bash).

userdel

Removes a user from the system. This can optionally remove the user’s home directory and mail spool.

Command Description
userdel <username> Removes the user but keeps the home directory and files.
userdel -r <username> Removes the user and deletes their home directory and mail spool.

groupadd

Adds a new group to the system. It assigns default group values unless further options are specified.

Command Description
groupadd <groupname> Creates a new group with the given name.
groupadd -g <gid> <groupname> Specifies a group ID (GID) for the new group.

To check group configuration, open the /etc/group file. The file defines groups on the system. It uses a colon : as a delimiter to separate the columns. Each line represents a group and contains the following information:

Col Field Name Description
1 Group Name The name of the group.
2 Password Usually marked as x, indicating the group’s password (if used) is stored separately.
3 GID (Group ID) A unique numerical identifier assigned to the group.
4 User List A comma-separated list of usernames who are members of the group.

Now the headers are more descriptive, aligning with the idea of explaining each part in a clear way!

groupdel

Removes a group from the system.

Command Description
groupdel <groupname> Deletes the group but does not remove users assigned to it.

usermod

Modifies an existing user’s properties such as their group, home directory, and shell.

Command Description
usermod -aG <group> <username> Adds the user to a supplementary group without removing them from other groups.
usermod -d <new_home> <username> Changes the user’s home directory.
usermod -s <new_shell> <username> Changes the user’s login shell.

passwd

Changes a user’s password or locks/unlocks the account.

Command Description
passwd <username> Changes the password for the specified user.
passwd -l <username> Locks the user’s account.
passwd -u <username> Unlocks a locked user account.

su

Switches the user to another account, usually the root user. It is often used to gain administrative privileges.

Command Description
su <username> Switches to the specified user’s account.
su - Switches to the root user and loads their environment.

groups

Displays the groups that the current user or a specified user belongs to.

Command Description
groups Shows the groups for the current user.
groups <username> Shows the groups for the specified user.