useradd : Creating and Managing User Accounts

Creating and Managing User Accounts 

useradd 

As its name implies, the useradd utility is used to add users to the Linux system.
The syntax for useradd is:


useradd options username 



For example, suppose I wanted to create a user account named lmorgan using default parameters.
I would enter


useradd lmorgan 


at the shell prompt.


• /etc/default/useradd 
  This file contains the defaults used by the useradd utility. Here is
  a sample:

  openSUSE:/ # cat /etc/default/useradd
  GROUP=100
  HOME=/home
  INACTIVE=-1
  EXPIRE=
  SHELL=/bin/bash
  SKEL=/etc/skel
  CREATE_MAIL_SPOOL=yes


  You can also view new user default values by entering

  useradd –D 

  at the shell prompt.



• /etc/login.defs 
  This file contains values that can be used for the GID and UID parameters
  when creating an account with useradd. It also contains defaults for creating 
  passwords in /etc/shadow. A portion of this file follows:


  openSUSE:/ # cat /etc/login.defs
  openSUSE:~ # cat /etc/login.defs
  #
  # /etc/login.defs - Configuration control definitions for the shadow package.



• /etc/skel
  The useradd command copies files from the skeleton directory (/etc/skel by 
  default) into a newly created home directory when you create a new user.


You can override these defaults when running

useradd 

by specifying a list of options in the command line. You can use the following:

• –c 
  Includes the user’s full name.


• –e 
   Specifies the date when the user account will be disabled. Format the date as
   yyyy-mm-dd.


• –f 
  Specifies the number of days after password expiration before the account is disabled.
  Use a value of
  –1
  to disable this functionality (for example, useradd –f –1 jmcarthur).


• –g 
  Specifies the user’s default group.


• –G 
  Specifies additional groups that the user is to be made a member of.


• –M 
  Specifies that the user account be created without a home directory.


• –m 
  Specifies the user’s home directory.


• –n 
  Used only on Red Hat and Fedora systems. By default, these distributions create a
  new group with the same name as the user every time an account is created. Using this 
  option will turn off this functionality.


• –p 
  Specifies the user’s encrypted password. You can encrypt the password you want to
  use with the

  openssl passwd -crypt 

  command. Run this command and, when prompted, enter the password you want to assign to the    user account.

  The command will output an encrypted version of the password on the screen. You can then use the encrypted password with the -p option of the useradd and usermod commands.


• –r 
  Specifies that the user being created is a system user.


• –s 
  Specifies the default shell for the user.

• –u 
  Manually specifies a UID for the user.





LX0-104 Exam Objectives (K)