Creating, Modifying, and Deleting User Accounts
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In this lesson, we will follow the lifecycle of a user account on a Linux/Unix system from creation, through modification, to deletion. We will also cover how to manage user groups.
Creating a User Account
useradd (Create New User Account) Let's start by creating a new user account named john:
sudo useradd -m -s /bin/bash johnHere is a breakdown of what that command does:
useradd: This is the command used to create a new user account.-m: This option instructsuseraddto create a home directory for the new user. The home directory will be created under/homewith the name of the user, in this case/home/john.-s /bin/bash: This option sets the login shell for the new user. Here,/bin/bashis specified as the login shell, which means that the Bash shell will be launched wheneverjohnlogs into the system.john: This is the name of the user account being created.
We can run list the contents of /home and should see the users new home directory:
ll /home/
# drwxr-x--- 2 john john 4096 Oct 3 01:08 john/Additionally, we can switch to the john user by running the following command:
sudo su johnThis will show us that we have switch to the john user:
john@ip-10-0-7-42:/home/iacadmin$We can exit that user by typing 'exit':
exitThis will show that you have switched back to your other user account (in our labs it is iacadmin):
iacadmin@ip-10-0-7-42:~$ Understanding the /etc/passwd File
The /etc/passwd file is a text file that describes user account information. Each line in the file represents a single user account and contains seven fields separated by colons (:). Here's the structure:
username:password:userID:groupID:userInfo:homeDirectory:shellusername: The name of the user.password: Anxcharacter indicates that encrypted password is stored in/etc/shadowfile.userID: The unique user ID (UID).groupID: The primary group ID (GID).userInfo: The user's real name or other information.homeDirectory: The absolute path to the user's home directory.shell: The absolute path to the user's login shell.
Let's view our new user account we just created by using grep to filter for john:
grep "john" /etc/passwdThis command will output information like the following:
john:x:1002:1002::/new/home/dir:/bin/bashYou will notice that the password field simply shows x in the /etc/passwd file's password field indicates that the actual encrypted password is stored in the /etc/shadow file, which is a more secure file accessible only by the root user. This change was made to enhance security, as the /etc/passwd file is readable by all users, whereas the /etc/shadow file has stricter access controls. More on the /etc/shadow file in a future lecture.
Modifying the User Account
usermod (Modify Existing User Account) Now, let’s change John’s username to john_doe and update his home directory:
sudo usermod -l john_doe john # Changes the username
sudo usermod -d /new/home/dir john_doe # Changes the home directoryDeleting the User Account
deluser (Delete User Account) Finally, let’s delete the john_doe user account:
sudo deluser --remove-home john_doeWe covered:
useradd: Create new user accounts.usermod: Modify existing user accounts and manage group memberships.deluser: Delete user accounts.
See you in the next lesson!
