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.