Posted on July 8, 2023 by nexonhost
How To List Users In Linux.
This tutorial will show you how to list users in Linux systems.
Get a List of All Users using the /etc/passwd File
Local user information is stored in the /etc/passwd file. Each line in this file represents login information for one user. To open the file you can either use cat or less :
less /etc/passwd
Each line in the file has seven fields delimited by colons that contain the following information:
User name.
Encrypted password (x means that the password is stored in the /etc/shadow file).
User ID number (UID).
User’s group ID number (GID).
Full name of the user (GECOS).
User home directory.
Login shell (defaults to /bin/bash).
If you want to display only the username you can use either awk or cut commands to print only the first field containing the username:
awk -F: '{ print $1}' /etc/passwdcut -d: -f1 /etc/passwd
root bin daemon adm lp sync shutdown halt mail operator games ftp nobody systemd-network dbus polkitd sshd postfix chrony nginx liviu.daniel tss vlad-test
Get a List of all Users using the getent Command
The getent command displays entries from databases configured in /etc/nsswitch.conf file, including the passwd database, which can be used to query a list of all users.
To get a list of all Linux userr, enter the following command:
getent passwd
As you can see, the output is the same as when displaying the content of the /etc/passwd file. If you are using LDAP for user authentication, the getent will display all Linux users from both /etc/passwd file and LDAP database.
You can also use awk or cut to print only the first field containing the username:
getent passwd | awk -F: '{ print $1}'getent passwd | cut -d: -f1
Check whether a user exists in the Linux system
Now that we know how to list all users, to check whether a user exists in our Linux box we, can simply filter the users’ list by piping the list to the grep command.
For example, to find out if a user with name jack exists in our Linux system we can use the following command:
getent passwd | grep vlad-test
If the user exists, the command above will print the user’s login information. No output that means the user doesn’t exist.
We can also check whether a user exists without using the grep command as shown below:
getent passwd vlad-test
Same as before, if the user exists, the command will display the user’s login information.
If you want to find out how many users accounts you have on your system, pipe the getent passwd output to the wc command:
getent passwd | wc -l
23
As you can see from the output above, my Linux system has 33 user accounts.
System and Normal Users
There is no real technical difference between the system and regular (normal) users. Typically system users are created when installing the OS and new packages. In some cases, you can create a system user that will be used by some applications.
Normal users are the users created by the root or another user with sudo privileges. Usually, a normal user has a real login shell and a home directory.
Each user has a numeric user ID called UID. If not specified when creating a new user with the useradd command, the UID will be automatically selected from the /etc/login.defs file depending on the UID_MIN and UID_MAX values.
To check the UID_MIN and UID_MAX values on your system, you can use the following command:
grep -E '^UID_MIN|^UID_MAX' /etc/login.defs
UID_MIN 1000 UID_MAX 60000
From the output above, we can see that all normal users should have a UID between 1000 and 60000. Knowing the minimal and maximal value allow us to query a list of all normal users in our system.
The command below will list all normal users in our Linux system:
getent passwd {1000..60000}
liviu.daniel:x:1000:1000::/home/liviu.daniel:/bin/bash vlad-test:x:1001:1001::/home/vlad-test:/bin/bash
Your system UID_MIN and UID_MIN values may be different so the more generic version of the command above would be:
eval getent passwd {$(awk '/^UID_MIN/ {print $2}' /etc/login.defs)..$(awk '/^UID_MAX/ {print $2}' /etc/login.defs)}If you want to print only the usernames just pipe the output to the cut command:
eval getent passwd {$(awk '/^UID_MIN/ {print $2}' /etc/login.defs)..$(awk '/^UID_MAX/ {print $2}' /etc/login.defs)} | cut -d: -f1Conclusion
In this tutorial, you learned how to list and filter users in your Linux system and what are the main differences between system and normal Linux users.