I recently installed Manjaro on an old laptop. Everything has been working fine, so far. Except when I try to access some features in settings and the package manager. When I try to access the Firewall Config or the Manjaro Settings Manager the system asks me for authentication. When I try to install packages from the package manager it too asks for authentication. Every time I enter my password it gives me an 'Authentication Failure'. During installation I did not ask it to create a root password. It is my understanding that the system would use my login password as the root password. If I use the terminal to install packages, and it asks me for my password, it accepts. Any thoughts/ideas? Any help would be appreciated. And before you ask, yes, I've posted to the Manjaro Forum and have gotten no help there.

It may be that the root password didn't "stick" somewhere, or there is a provision that doesn't let a regular user use root credentials in certain situations. You said that it accepts your password in a terminal. If you can get super user in the terminal, you can change the root password. Commands as follows.

su
your password
"granted root access"
passwd root

It should prompt you for a new password. I believe that you are allowed to use the same password as you had. The reason that I suggest this is that it should reset the root password "across the board" in case the problem is caused by some kind of undiscovered bug. If that doesn't help,I have no other idea.

It's generally a good idea to set a root password during install. openSUSE asks if you want to use your user password for root during install. If you decline, I believe it asks you to set a root password. Is it possible that Manjaro asked in a dialogue and you missed it? I'm just asking because I have never used Manjaro.

Ok, I got mixed results with your method. I can use the package manager now but when I try to, for example, open the Firewall Configuration in the Settings it continues to give me an Authentication Failed error when I enter in the root password. There are certain options in the Settings in which I don't have access to because of this.

When you install Manjaro, on the screen where it asks you for your login name and password, there is a option to set a root password. If you opt not to then the system is supposed to use your login password as the root password. I was able to create a root password with your method but it only seems to have affected the package manager.

I found in another forum that "policy kit" has to run after first login during startup or a person can have problems like you mention. You never mentioned which desktop you use, so I can't be sure where you can find settings for "startup programs".

Is there a way to open the settings manager as su or root, rather than open it as your user and have to get admin privileges for each section of settings? That's not a very secure way to do things, but it may get you into what you want to do, at least temporarily.

Did you check the hash of the install medium to verify it before the install? I've seen a lot of strange things happen from an install medium error. I am not familiar with pacman. Is there a way to verify that all package dependencies are met?

Manjaro is a derivative of archlinux from what I read. If the Manjaro forums can't help, maybe archlinux has answers.

Sorry, I'm running Xfce

I'm not sure how to open the settings as root.

To fix the problem just reinstall polkit using sudo pamac reinstall polkit in the terminal