A much better idea is to set up a non-root user and configure sudo correctly.
* https://www.stigviewer.com/stigs/red_hat_enterprise_linux_9/...
There isn't more than one UID 0. Only more than one password/shadow database entry pointing to it.
(It might not be necessary; perhaps there is a way for OpenSSH to remap names, so that our example rotorooter is mapped to root by sshd itself.)
> A much better idea is to set up a non-root user and configure sudo correctly.
Even if so, the same principle applies: do not call that user admin, for instance. Don't use your first name or anything that a targeted, non-random attacker could guess about you.
If that user's name is, oh, 7yMfAxB6, it will never be probed. Though no need to be that paranoid.
From the document:
> Multiple accounts with a UID of "0" afford more opportunity for potential intruders to guess a password for a privileged account.
Whoever wrote that does not know WTF they are talking about. Two identical entries in passwd/shadow do not comprise different "accounts".
The UID is the account; the password DB is more or less just window dressing.
If the two shadow entries have exactly the same password hash, then no, there aren't more opportunities to guess a password.
The only problem with the scheme in a multi-user institutional context is that when an additional UID 0 entry appears that is not "root", it looks like a backdoor someone planted to give themselves continued root access.
I don't think it's applicable to what I'm talking about because an institution probably shouldn't be setting up password-based SSH access to a renamed root account over the public internet. This is something that's a good solution for individuals or very small operators.
> Change the UID of any account on the system, other than root, that has a UID of "0".
Change it to what, with what desired effect? Might as well say 'oh, screw with the password file randomly for shits and giggles'.
Better idea: investigate why there is another 0. Maybe there is a good reason.
... or they know something you don't.
It has the same optics as an unauthorized entry someone planted: a backdoor to retain root access. It will continuously have to be explained to new people who spot it.
If the intent is to keep the passwords identical (which it probably should be), the tooling doesn't support it. When someone changes the password for root using standard tools, the one for rotorooter doesn't sync. This is a problem if someone is changing the password in order to restrict access to just a specific set of people who know the new password. The unaltered entry turns into a de facto backdoor for everyone knowing the old password.
Pitafall: if you put an alias entry in the wrong spot in in the password file, so that it appears before the canonical entry, then UID 0 maps backward to the alias name (e.g. via the getpwuid() function). This breaks all logic that looks for the string "root" rather than UID 0. E.g. shell scripts looking for root in the output of some command.
The kind of organization where it would make sense to forbid tricks like multiple password entries pointing to the same user (such as UID 0) is going ot be the kind of organization where the whole thing is moot anyway in connection with SSH, because in those kinds of organizations, you don't want ad hoc machines to be accessible via SSH publicly. You don't want employees to be solving the problem of SSH ports being probed: do we use fail2ban, port knocking, kazinator's user name tricks posted on HN? ... just no! You have some kind of perimeter VPN. Authorized users connected to the VPN can then use SSH to machines inside the secured zone.
It makes no sense to bring up corporate rules against my solution which for a problem that corporations should not have in the first place: SSH-accessible machines on the open internet being probed.
I don’t recall ever seeing a security requirement not to have 2 root accounts. What you can’t have is multiple users sharing the same account. This is different.
I'm wildly guessing that the BSD flavors that have toor have patched their password DB manipulation utilities and APIs such that when you change the root password, the toor one changes with it and vice versa.
> The reason it exists is shell flexibility. Traditionally root's shell is kept as a statically-linked shell like /bin/csh or /bin/sh so that the superuser can always log in even in single-user mode or if dynamically-linked shells in /usr/local break. The toor account lets an admin have a UID 0 login with a fancier daily-driver shell (bash, zsh, etc.) without touching root's safe configuration.
Could I trouble you to specify? Your link only seems to mention password problems that are trivially avoidable (really, if doubling the guesses is a problem, you're already done).