Shell command useradd

useradd creates a new user or updates default new user information.

It is a low level utility, an alternative is adduser.

$ useradd -s /bin/bash -m rene

-s specifies the default shell for the new user. If not specified, it takes the value of SHELL variable in /etc/default/useradd.

-m creates the new user's home directory if it does not exist.

command line options

$ useradd ---help
useradd [options] LOGIN
useradd -D
useradd -D [options]

	`--badnames`		Do not check for bad names
`-b`	`--base-dir`	`BASE_DIR`	Base directory for the home directory of the new account
	`--btrfs-subvolume-home`		Use BTRFS subvolume for home directory
`-c`	`--comment`	`COMMENT`	GECOS field of the new account
`-d`	`--home-dir`	`HOME_DIR`	Home directory of the new account
`-D`	`--defaults`		Print or change default useradd configuration
`-e`	`--expiredate`	`EXPIRE_DATE`	Expiration date of the new account
`-f`	`--inactive`	`INACTIVE`	Password inactivity period of the new account
`-g`	`--gid`	`GROUP`	Name or ID of the primary group of the new account
`-G`	`--groups`	`GROUPS`	List of supplementary groups of the new account
`-h`	`--help`		Display this help message and exit
`-k`	`--skel`	`SKEL_DIR`	Use this alternative skeleton directory
`-K`	`--key`	`KEY=VALUE`	Override `/etc/login.defs` defaults
`-l`	`--no-log-init`		Do not add the user to the lastlog and faillog databases
`-m`	`--create-home`		Create the user's home directory
`-M`	`--no-create-home`		Do not create the user's home directory
`-N`	`--no-user-group`		Do not create a group with the same name as the user
`-o`	`--non-unique`		Allow to create users with duplicate (non-unique) UID
`-p`	`--password`	`PASSWORD`	Encrypted password of the new account
`-r`	`--system`		Create a system account
`-R`	`--root`	`CHROOT_DIR`	Directory to chroot into
`-P`	`--prefix`	`PREFIX_DIR`	Prefix directory where are located the `/etc/*` files
`-s`	`--shell`	`SHELL`	Login shell of the new account
`-u`	`--uid`	`UID`	User ID of the new account
`-U`	`--user-group`		Create a group with the same name as the user
`-Z`	`--selinux-user`	`SEUSER`	Use a specific SEUSER for the SELinux user mapping

Adding a user to a group (for example sudo)

usermod can be used to add an already created user to an already created group:

$ usermod -a -G sudo rene

Make sure that /etc/sudoers is configured to allow users in the sudo group to execute sudo commands.

Populating the users home directory (-k)

By default, the home directory of a new user is populated with the files from the SKEL variable in /etc/default/useradd (default: /etc/skel/*).

This directory can be overwritten with -k /path/to/directory.

In order to not create any files in the home directory, use -k /dev/null.

Not adding the user to the faillog and lastlog databases (-l)

When -l is specified, the user is not added to the faillog and lastlog databases.

Do not create /var/spool/mail/_user_

The following command prevents the creation of the /var/spool/mail/_user_ directory:

useradd -K MAIL_DIR=/dev/null …

This command prints the following warning which can be ignored:

Creating mailbox file: Not a directory

Changing the user's password

After creating a user, the password for the user might be set with passwd

useradd -m rene
passwd rene

Alternatively, the following command allows to set the password in a script

echo 'rene:theSecret' | chpasswd

Defaults

Some defaults (such as if a Home directory should be created) are configured in /etc/login.defs