Managing Users & Groups
under GNU/Linux

Serge Y. Stroobandt

Copyright 2014–2019, licensed under Creative Commons BY-NC-SA

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Users & Groups

List all users

$ cat /etc/passwd

List all groups

$ cat /etc/group

Always use adduser or addgroup

The useradd, userdel and usermod commands are lowlevel utilities which are there for historical reasons, while adduser/deluser Do The Right Thing™.

adduser and addgroup add users and groups to the system according to command line options and configuration information in /etc/adduser.conf. They are friendlier front ends to the low level tools like useradd, groupadd and usermod programs, by default choosing Debian policy conformant UID and GID values, creating a home directory with skeletal configuration, running a custom script, and other features. adduser and addgroup can be run in one of five modes:

Manpage for useradd says:

useradd is a low level utility for adding users. On Debian, administrators should usually use adduser(8) instead.

$ sudo adduser username
$ sudo adduser username --uid 1005
$ sudo addgroup groupname --gid 2000

Mnemonics

Naughty mnemonics are the ones that are best remembered, so here it goes:

The word “user” rhymes with “loser”, and “loser” comes last.
Thus, it is: adduser & deluser.

Create an SSH key pair

mkdir $HOME/.ssh
chmod 600 $HOME/.ssh
ssh-keygen -t rsa -b 4096 -f $HOME/.ssh/id_rsa
ssh-add $HOME/.ssh/id_rsa

Change a user’s finger information

$ man chfn

Delete an existing user

$ sudo deluser --remove-home username

List a user’s group membership

The id command offers much more information than the group names listed by groups. UID, primary GID and other group IDs are listed as well.

$ id username
$ groups username

Add an existing user to an existing group

$ sudo adduser username groupname

Log out and in again for this group affiliation to take effect.

Delete an existing user from an existing group

$ sudo deluser username groupname

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