How does the administrator/root/superuser work in Linux?

Question

We were taught Windows when I was in School. I then opted for a Bachelor course in Computer Engineering where we were made to use Linux instead of Windows. They never taught about basics of Linux and directly started teaching programming. It was not that difficult for me because I was somewhat familiar with Linux. But still I have some doubts about the administrator or root or superuser system in Linux. Now my question comprises of several different sub questions. So here it goes:

1. I know that # (hash) in the terminal prompt means that one is operating as a superuser and $ (dollar) means that one is not. But even though my account is an Administrator account I don't see # on my terminal prompt. Instead I have to login using the su command to have Administrative rights. Why is that?

2. Are the terms Administrator, root and superuser same? I'm confused because in Windows, there is just one term Administrator and if your account is an Admin account, then you are basically logged in with Admin privileges all the time i.e. one doesn't have to explicitly log in as an Admin unlike in Linux.

3. We have Ubuntu installed in our College computers where if you have to log in as admin, then you type in su and then it prompts for password where you have to enter your current account password to become the superuser. But I didn't like the Ubuntu design so I switched to and installed Fedora on my laptop where the installation asked me for Two passwords, one for my normal account (which has admin rights) and the other for the 'root' user. So does that mean whenever I have to login as an admin using my normal account then I have to login my 'root' password instead of my normal password? And if that's the case, why did the software asked for my normal password if it won't give me the admin rights directly?

EDIT:

Can someone explain me the admin system in Linux? What is root? Why do I not have admin rights despite being an admin?

Answer 1

Every account on a Unix/Linux system has a numeric identifier, the "user ID" or UID. By convention, UID 0 (zero) is named "root", and is given special privileges (generally, the permission to access anything on the system).

You could just log in as the root user directly, if you have the root password. However, it's generally considered bad practice to do so.

For one thing, it's often the case that Unix/Linux gives you plenty of room to shoot yourself in the foot with no safety — there are many typos and accidents from which the easiest recovery is to do a complete reinstall and/or restore from backup. So, having to actually switch to root when you need to keeps you from accidentally doing something you didn't mean to.

It also helps limit the spread of malware. If your web browser is running under UID 0 — "as root", we say — then a programming bug could be exploited by remote websites to take complete control over your computer. Keeping to a "regular" user account limits that damage.

Both of these follow a general best practice called "the principle of least privilege" — which, honestly, is a good thing to follow in system design in general. You can read more in specific about reasons to not always run as root under Concern about logging in as root overrated?

Now, that leaves the question of how you can get access to protected things as a non-root user. There are two basic ways — su and sudo. The first requires the root password, and the second, in usual configuration, requires your password. It's often the case that you use sudo to run a single command "as root", rather than switching to the root account for a whole session. (You can also do this with su -c, something you will often see in documentation.) For a long discussion of the relative merits of these, see Which is the safest way to get root privileges: sudo, su or login?. (And, for completeness, there are other mechanisms which aren't sudo but work in the same way, like PackageKit, usually used for GUI applications.)

You ask whether the terms "root", "superuser", and "administrator" are the same. "Root" and "superuser" basically are. To be precise, one might say: "The root account is the superuser, because it has UID 0."

"Administrator" could mean the same thing, but in Fedora, we* use it in a slightly different way. Not every user on the system has the power to get root privileges via sudo. In Fedora in the default setup, members of the group wheel can do this. And, in the installer and in the documentation and other places, we call this an "administrator account". One that isn't root, but has the power to access root privileges.

(Oh, and one final thing: that # vs $ in your prompt is just a visual convention and isn't definitive. You can change the environment variable PS1 to make the prompt do all sorts of things.)

* I work on Fedora.

Answer 2

1. Security concern, see https://askubuntu.com/questions/16178/why-is-it-bad-to-login-as-root

2. Yes

3. su allows to run commands with a substitute user, when called without arguments it defaults to run a interactive shell as root. See http://www.linfo.org/su.html You need to have the root password for this.

   You can bypass this by running sudo su (if you're allowed to run this). Sudo allows a permitted user to execute a command as the superuser or another user, as specified by the security policy. (specified in the /etc/sudoers file). Read more here: https://www.sudo.ws/man/1.8.15/sudo.man.html

   So for your final questions. As for the first one, yes. But most people prefer to use sudo for the convenience. And as for the final one: I'm not sure what you mean, but it's preferable to have different passwords for different accounts.

Answer 3

Windows and Linux don't manage administration privileges in the same way.

In Windows, system administration tasks can only be performed by processes running at a high privilege level. Normal processes run at a normal privilege level. A user can run a process at high privilege level if their account is marked as administrator; normally, they need to re-enter their password to do that (the “UAC prompt”). Thus an administrator is a user whose account has the right to elevated privileges.

In Linux (and other Unix systems), system administration tasks can only be performed by the root user. That's a user account which is intended for system tasks, not for a human to log in. The root user is defined by its user ID, which is 0 (the account is normally called root, but it's the user ID that makes it special, not the name). An administrator is a user who has the right to access the root account.

There are two main ways in Linux to access the root account. The system administrator may enable one or both or them (or more rarely other methods, involving either the same tools configured differently or other tools).

• The su command allows any user to access the root account if they know the password for the root account. In some setups, only certain users who are members of a group traditionally called wheel are allowed to use su to run commands as root.
• The sudo command allows a user to run commands as root if they are declared in the sudo configuration file (sudoers), either directly or via a group membership. Usually sudo requires the user to enter their own password; this is mostly to avoid sudo being used by a passerby if the user left their terminal unattended.

So if you have an administrator account on Linux, it means you're allowed to run sudo or su to run commands as root. When you aren't running commands as root, you have normal privileges.