As a Linux administrator, you must know how to add, delete and grant sudo privileges to users. Sometimes, you may give temporary sudo access to regular users for specific tasks like software installation or administrative work. Over the time, you might forget to revoke the sudo privileges. To ensure security, it's a good practice to periodically check for super users with sudo access on your Linux system. If you find any forgotten or unnecessary sudo access, you can simply revoke them. This brief guide explains how to find all sudo users in Linux and Unix-like operating systems.
Display All Users
Let us first list all users in the system. To do so, run:
$ awk -F':' '{ print $1}' /etc/passwdSample output from my Ubuntu system:
root daemon bin sys sync games man lp mail news uucp proxy www-data backup list irc gnats nobody systemd-timesync systemd-network systemd-resolve systemd-bus-proxy syslog _apt lxd messagebus uuidd dnsmasq sshd sk senthil kumar ostechnix
Another way to list all users in a Linux system is:
$ compgen -u
For more methods to display all users in Linux, check the following guide.
List Sudo Users in Linux
In most Linux distributions, members of the "sudo" or "wheel" group are granted sudo privileges. To see the members of the "sudo" group, you can use the getent command or simply list the contents of the /etc/group file:
To find all sudo or super users in Linux, use getent command like below:
$ getent group sudo
Sample output:
sudo:x:27:sk,ostechnix
Explanation of the output:
sudo: This is the name of the group. In this case, it is the sudo group, which typically grants members sudo (superuser) privileges.x: This field represents the group password, which is usually not used in modern Linux systems. Hence, it is typically set to "x" or a placeholder.27: This is the group ID (GID) assigned to the sudo group.sk,ostechnix: These are the members of the sudo group.
In summary, the output shows information about the sudo group, its group ID, and users called "sk" and "ostechnix" who has sudo privileges on the system. This user can perform administrative tasks using the sudo command.
Alternatively, you can identify all sudo users by listing the contents of the /etc/group file:
$ cat /etc/group | grep '^sudo:' sudo:x:27:sk,ostechnix
As you see in the above output, "sk" and "ostechnix" are the sudo users in my system.
You can get the simplified output by excluding other parameters and listing only the names of the sudo users like below.
$ getent group sudo | cut -d: -f4 sk,ostechnix
Let us break down the command and see what each parameter does.
The above command is a combination of two Linux commands:
getent group sudo: This command retrieves information about the "sudo" group from the system's database. Thegetentutility is used to query the Name Service Switch (NSS) databases, and in this case, it fetches the details of the "sudo" group.cut -d: -f4: The output of the previous command is then piped (represented by the|symbol) to thecutcommand, which is used to extract specific fields from the input data. In this case, it splits each line of input using the ":" character as the delimiter (-d:), and it selects the fourth field (-f4).
So, the purpose of this command is to retrieve and display the list of user IDs (UIDs) that are members of the "sudo" group.
Each line in the output represents a user ID that belongs to the "sudo" group. The user IDs listed in the output are typically used to map the users to their respective names in the /etc/passwd file.
You can also use "grep" command to filter the names of the sudo users from the file /etc/group and get the same result as the previous command.
$ grep '^sudo:.*$' /etc/group | cut -d: -f4 sk,ostechnix
As mentioned earlier, being a member of the sudo group allows the user to execute commands with elevated privileges using the sudo command.
Find if an User has Sudo Privileges
We know now how to find all sudo users in our Linux system. How to find whether a certain user has sudo privilege or not? It's easy to check individual user sudo access!
If you want to check sudo access for a specific user, you can use the sudo -l command:
$ sudo -l -U sk
This command will help you to find if an user is sudo user or not.
Sample output:
Matching Defaults entries for sk on ubuntuserver: env_reset, mail_badpass, secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin User sk may run the following commands on ubuntuserver: (ALL : ALL) ALL
As you see, the user named "sk" can perform all commands. So, he is in the sudo group.
Let us check another user.
$ sudo -l -U senthil
Sample output:
User senthil is not allowed to run sudo on ubuntuserver.
Well, the user "senthil" is not allowed to run sudo. He is just a regular user!
We can also find if an user has sudo access by running the following command:
$ sudo -nv
If the output shows nothing, the user has sudo access.
If you see an output like below, then the user doesn't has sudo access.
$ sudo -nv Sorry, user senthil may not run sudo on ubuntuserver.
Frequently Asked Questions
A: In Linux, sudo users are regular users who have been granted special privileges to perform administrative tasks. They can use the "sudo" command to temporarily elevate their privileges and execute commands as a superuser (root) without logging in as the root user.
A: You can find all sudo users in Linux using different methods. One way is by checking the "sudo" group in the /etc/group file using the following command:cat /etc/group | grep '^sudo:'
This will display a list of users who are members of the "sudo" group, typically having sudo access.
A: While the sudo -l command is useful to check the sudo privileges of a specific user, it does not directly provide a comprehensive list of all sudo users on the system. It's more suitable for verifying an individual user's sudo permissions.
A: It is essential to periodically check for sudo users on a Linux system to ensure security and proper privilege management. Over time, temporary sudo access might be forgotten or not revoked, potentially leading to security risks. By identifying all sudo users, administrators can review and control who has elevated privileges on the system.
A: Yes, the same approach can be used to check for sudo users on Unix-like systems, such as macOS, FreeBSD, or other UNIX-based operating systems. The sudoers file and group configuration may differ slightly, but the general method remains similar.
Conclusion
By knowing how to find all sudo users in Linux, you can better manage sudo access on your system. This can help to ensure that only authorized users have access to sudo privileges, and that sudo access is not being abused.
I hope this helps.
2 comments
Thanks a lot! “compgen -u” did it for me!
I’m using this script to find out sudo users, and then call this script with ansible and fetch the files.
Script:
#!/bin/bash
FILEPATH=”/tmp”
USRFILE=$FILEPATH/userlist.txt
GRPFILE=$FILEPATH/grouplist.txt
USRSD=$FILEPATH/userrights.txt
GRPSD=$FILEPATH/grouprights.txt
SUDOUSERS=$FILEPATH/adminuser.txt
#rm -rf $SUDOUSERS 2>&1
grep -v ‘#’ /etc/sudoers | awk ‘{print $1}’ | sed ‘s/Defaults//g’ | sed ‘/^$/d’ >> $USRFILE
for id in `cat $USRFILE`;do
echo “$id” >> $USRSD
done
sed -i ‘/%/d’ $USRSD
grep “[] % []” $USRFILE | tr -d ‘%’ >> $GRPFILE
for grp in `cat $GRPFILE`;do
groupmems -g $grp -l >> $GRPSD
done
cat $USRSD $GRPFILE >> $SUDOUSERS
rm -rf $USRFILE $GRPFILE $USRSD $GRPSD 2>&1
Ansible Play:
– name: Get Sudo Users and Write to File
hosts: web
become: yes
gather_facts: yes
tasks:
– name: Get sudo users
script: /home/thor/ansible/script.sh
args:
executable: /bin/bash
– name: Fetch Files from Systems
fetch:
src: /tmp/adminuser.txt
dest: /tmp/sudo_users-{{ inventory_hostname }}
flat: yes