4

I am reading this tutorial, and trying to create a new user with root privileges and then block root access via ssh in a CentOS 7 server. The problem is that the new user is blocked from doing root actions like nano /etc/sudoers. Also, I seem unable to remove the block of root login. So my pre-existing open root session is the only access I have to root functionality until it terminates. How can I successfully add root permissions to the newuser? And how can I successfully turn on/off root login?

Here is what I have so far:

In /etc/sudoers, I have:

## Allow root to run any commands anywhere
root    ALL=(ALL)   ALL
newusername  ALL=(ALL)  ALL

Note that I edited /etc/sudoers because /usr/sbin/visudo did not work.

In /etc/ssh/sshd_config I have PermitRootLogin yes because I want to turn root login back on until I can get newusername to have root privileges. Also, the last line of the file is AllowUsers newusername.

I then typed systemctl reload sshd.service because /etc/init.d/sshd reload threw an error on CentOS 7.

The problem is that currently newusername does not have root privileges and yet I am not able to login as root either. So my pre-existing connection as root is my only way of controlling the machine.

EDIT #1

I was able to give the new user sudo privileges with gpasswd -a newusername wheel, but I still cannot log in as root even though I have PermitRootLogin yes in /etc/ssh/sshd_config. How can I get CentOS 7 to respect the settings in /etc/ssh/sshd_config? I should be able to turn root login on and then off again at will, and have the settings actually work.

  • Anytime you change the contents of sshd_config you will need to either reboot your system or restart the sshd daemon. – mdpc Dec 18 '14 at 8:16
  • @mdpc the server is on a remote network. i am logging into it via ssh. Do I have to get someone at the physical location of the server to restart the sshd daemon? I am concerned that running systemctl stop/start sshd.service remotely via ssh would cause my connection to close after the stop and before the start, thus locking me out. – CodeMed Dec 18 '14 at 16:52
  • 1
    For that matter, /etc/sudoersshould not be edited unless using visudo – eyoung100 Mar 8 '15 at 2:19
5

I am reading this tutorial, and trying to create a new user with root privileges and then block root access via ssh in a CentOS 7 server. The problem is that the new user is blocked from doing root actions like nano /etc/sudoers. Also, I seem unable to remove the block of root login. So my pre-existing open root session is the only access I have to root functionality until it terminates. How can I successfully add root permissions to the newuser? And how can I successfully turn on/off root login?

  1. Strictly speaking, the real use of sudo is to configure the execution of certain specific commands to certain specific users or groups. The way sudo is distributed and configured in some distributions can be somewhat misleading because to become the root user, we can just type su - without involving sudo. This requires the entry of the password for the user, root, and not the user's password. So you could have used this.
  2. Try to never use anything except visudo to directly edit /etc/sudoers. Otherwise you could break authentication altogether until you change its permissions back to 0400 (which you cannot do after you log out without utilizing a rescue system of some sort). (The editor used by visudo can be controlled by the VISUAL environment variable. To use it with nano, one option is VISUAL=nano visudo.)
  3. The new user already can become root (point 1), but to let this user become root though sudo, just add the user to the right group. On CentOS 7, the traditional group name of wheel was used to allow members of that group to become root via sudo: usermod -a -G wheel codemedic. Use man usermod for more details. You can determine this group name by reading the configuration file: cat /etc/sudoers.
  4. To deny access to root via SSH, edit /etc/ssh/sshd_config and make sure that only one uncommented instance of PermitRootLogin is available and set it to a value of no: PermitRootLogin no. Save the file and restart the Secure Shell daemon: systemctl restart sshd.

Note that I edited /etc/sudoers because /usr/sbin/visudo did not work.

How does visudo not work?

  • Thank you and +1 for taking the time to write an informative answer. – CodeMed Jun 20 '15 at 1:24
6

The way CentoOS grants root(all) privileges to a user is by putting them in the wheel group. This is what happens when you make a user account and select the box that makes that user an Administrator.

You can put a user in a group with:

sudo usermod -aG wheel username

To disable an account from logging in, including the root account you can lock it by setting a non usable password.

sudo passwd -l username

  • Your response is similar to the gpasswd -a newusername wheel in the 2014 edit to the OP above. Technically, sudo only lets users do some root operations. There are still certain commands which a sudoer cannot execute unless they su - to actually become root. I think a good answer would describe how to create the someuser account privileges that would enable them to perform any command if another user elevates to that account via su - someuser. But I am giving this +1 because you took the time to respond to an old posting. Thank you. – CodeMed Mar 3 '17 at 18:14
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These steps worked for me.

Add user:

useradd user

Add password:

passwd user

Add following line to the /etc/sudoers file by using the command visudo:

user ALL=(ALL)       ALL

or, for becoming root without having to enter a password,

ALL ALL=(ALL) NOPASSWD:ALL

Then, switch to that user

su user

and ask for root privileges:

sudo su - 

Enter password for new user:

[sudo] password for user:

protected by Archemar Aug 4 '17 at 12:56

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