LinuxCommandLibrary

Users & Groups

Creating Users

useradd is the low-level tool: add -m to create a home directory and -s to set the login shell. On Debian-based systems, adduser is the friendlier interactive front end. All user and group administration requires root.

$ useradd -m -s /bin/bash [name]

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$ adduser [name]

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$ passwd [name]

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Plain useradd [name] creates the account without a home directory, which is rarely what you want for a real user.

Deleting & Renaming Users

-r also removes the user's home directory and mail spool.

$ userdel [name]

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$ userdel -r [name]

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$ deluser [name]

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$ usermod -l [newUsername] [oldUsername]

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Modifying Users

Change a user's shell, home directory, or comment field.

$ usermod -s /bin/zsh [name]

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$ chsh -s /bin/zsh [name]

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$ usermod -d /new/home -m [name]

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Lock an account (disables password login) and unlock it again.

$ usermod -L [name]

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$ usermod -U [name]

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Force a password change at next login, or inspect password aging.

$ passwd -e [name]

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$ chage -l [name]

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Groups

Create, rename, and delete groups.

$ groupadd [name]

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$ groupmod -n [newGroupname] [oldGroupname]

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$ groupdel [name]

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Add an existing user to a group. The -a in -aG is essential: without it, the user is removed from all other supplementary groups.

$ usermod -aG [groupName] [userName]

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$ gpasswd -a [userName] [groupName]

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$ adduser [userName] [groupName]

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Remove a user from a group.

$ gpasswd -d [userName] [groupName]

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$ deluser [userName] [groupName]

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Group changes take effect at the next login. Use newgrp [groupName] to activate one in the current shell without logging out.

Granting sudo

Membership in the admin group grants sudo rights: the group is sudo on Debian/Ubuntu and wheel on Fedora, RHEL, and Arch.

$ usermod -aG sudo [user]

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$ usermod -aG wheel [user]

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Edit the sudoers file only with visudo, which checks the syntax before saving (a broken sudoers file can lock you out).

$ visudo

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Listing Users & Groups

getent queries all account databases, including LDAP and other network sources; the /etc files only show local accounts.

$ getent passwd

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$ getent group

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$ cat /etc/passwd

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$ cat /etc/group

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Who Am I, Who Is Here

Show the current user, their IDs and groups, and the groups of any user.

$ whoami

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$ id [user]

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$ groups [user]

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See who is logged in and what they are doing, and the login history.

$ who

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$ w

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$ last

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Switching Users

su - starts a full login shell as another user (root if no name is given); sudo -i opens a root shell via sudo.

$ su - [user]

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$ sudo -i

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$ sudo -u [user] [command]

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