Linux Fundamentals 4: User Management
- In Linux users and groups are used for access and permissions.
- Each user has their own UID and home directory.
- When running a process it will run as the owner of the process.
- Groups are a set of users with permissions set by the group.
- The superuser or root is the most powerful user - use sudo to run the with root
To view the user configuration you can look in the /etc/passwd file
The user is displayed in the following format.
username : user password (if x stored elsewhere) : user id : user group id : GECOS field (comments) : user home directory : users shell
The /etc/shadow file stores info about the users authentication.
sudo cat /etc/shadow
The results can be read in the following format.
username : encrypted password : date of last password changed : minimum password age : maximum password age : password warning period : password inactivity period : account expiration date : reserved field for future use
The /etc/group shows groups with the assigned users.
The results can be read in the following format
group name: x : group id : list of users
Add a User
For this example I will create a user called 'aem'.
sudo useradd aem
check the user exits by running
We can see the user is assigned 1001, this is because id's + 1000 plus are reserved for local users. system users are assigned 1 to 999. Id 0 is always for the root user.
Set the user password
To set the users password I will run the following command.
sudo passwd aem
You will be asked to set the password. Once complete check /etc/shadow and you will see the created authentication for the AEM user.
Modifying a User
The usermod command can be used to modify the users configuration. Some of the common uses are below. Use man usermod for full details
- Add/Modify a users group
- Change GECOS - user info
- Change user home directory.
- Change user Shell
Delete a User
To delete a user you can use the userdel command.
sudo userdel aem
you can confirm removal by checking the /etc/passwd/.
Next up in part 5 of Linux fundamentals we will discuss user permissions.