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Account Basics

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Account Settings

Account settings and details are stored in some of the following directories and files.

  • /etc/login.defs - Site-specific configuration for the shadow password suite, configuration options
  • /etc/passwd - Main file system used to track user accounts
  • /etc/default/useradd - The useradd program uses a collection of default values kept in this file
  • /etc/shadow - Location of (user) hashed passwords
  • /etc/group - Group information
  • /etc/gshadow - Location of (group) hashed passwords

The useradd command modifies the passwd, shadow, group, and gshadow files

Every user will belong to a single primary group, which is listed in the passwd file. A user can also belong to multiple secondary groups.

Adding and Removing Accounts

Adding and removing accounts with explanations and argument options.

Command Description
useradd accountname Create user. Makes a home directory and gives it default shell
userdel accountname Delete user. Doesn’t fully remove everything, use -r arguments
userdel -r accountname Deletes the user and associated mailbox/directory stuff
passwd deleteme Deletes the password and allows you to create a new one

Unique IDs and Directories

Command Description
useradd -u 1500 username u option Specifies a unique user ID (instead of default)
useradd -g 1501 username g option Specifies a unique group ID (instead of default)
useradd -d /home/user8 u8 d option Adds the user with a home directory of /user8 instead of the username “u8”
useradd -M user9 M option Doesn’t create a home directory
*ID numbers 1500, 1501, 1501 have no special meaning

Unique IDs and Directories

Adding and removing accounts with explanations and argument options.

Command Description
useradd -u 1500 username u option Specifies a unique user ID (instead of default)
useradd -g 1501 username g option Specifies a unique group ID (instead of default)
useradd -d /home/user8 u8 d option Adds the user with a home directory of /user8 instead of the username “u8”
useradd -M user9 M option Doesn’t create a home directory
*ID numbers 1500, 1501, 1501 have no special meaning

Shells

The default shell specifies what program or process will be started when the user logs in.

Command Description
useradd -s /bin/tcsh username s option Sets the shell, here we specified tcsh
useradd -D D option Shows you what it can change
useradd -D -s /bin/tcsh D -s Changes the default shell for all new users

Groups

Groups make it easier to control permissions for multiple users.

Command Description
id username Display users UserID, GroupID, and what groups they are in
groups username Display the group the user is in
groupadd groupname Add a group
groupdel groupname Remove a group
usermod -a -G groupname username Assign a secondary group to a user
gpasswd -d username groupname Remove a user from a group

Finger

The default shell specifies what program or process will be started when the user logs in.

Command Description
chfn username As root you can change this for a user
useradd -c “FirstName LastName” username Don't use quotes if you only want to change first name
useradd -c “Firstname Lastname,New York,444-4444,555-5555” username Changing additional fields