Ubuntu – the password for “ssh root@localhost“

rootssh

I need to ssh to localhost using root account, by ssh root@localhost. When it prompts for passwords, I can not login with all possible passwords. On setting of localhost machine, regular user xxx and root user share the same password (the password that works for sudo -s), but it does not works for ssh root@localhost. So where to look at the password for ssh root@localhost

PS: with the password, I can login to regular account on ssh xxx@localhost.

PPS: to answer further questions on motivation of doing so, localhost is just a computer in a private network and setting up ssh root@localhost is just to relieve some manual management in a prototype system.

Best Answer

ssh root@localhost uses the same password for root. It looks like you have not set root password. To do that log in as root using sudo -s then use passwd command to set root password.

After that you must be able to ssh as root

How to find out root password for installing software

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Ubuntu – meant by “no password set” for root account (and otthers)

What is meant by an unset password? Is it blank? Is it null? Or something else more cryptic?

Is just inexistent. Root account is disabled by default, hence it doesn't need password. So, what most resemblance has is undefined (in JavaScript) or (null) (other languages). It is just unset.

How does the account becomes enabled once I set password for it?

Actually, setting the password is just part of it, but doesn't enable the account. You need to enable the account using:

sudo usermod -U root

and then set the password with passwd.

what does an ! in password field mean?

Extracted from man shadow:

A password field which starts with a exclamation mark means that the password is locked. The remaining characters on the line represent the password field before the password was locked.

It could mean that the account is locked. But also:

If the password field contains some string that is not a valid result of crypt(3), for instance ! or *, the user will not be able to use a unix password to log in (but the user may log in the system by other means).

Either way, any account with ! can't log in with applications that use the shadow file.

How come this encrypted form is only one character long?

Is not encrypted. See above.

And does an account become disabled if I put an ! in the (encrypted) password field?

See above too.

Ubuntu – Disabling SSH password login for Ubuntu

set "UsePAM no" in sshd_config file

You don't want to turn of PAM.

If I want to be able to login as root and otheruser using only SSH keys, what changes do I make?

To achieve this, these options are related:

PermitRootLogin without-password
ChallengeResponseAuthentication no
PasswordAuthentication no
AllowUsers root otheruser
PubkeyAuthentication yes     # missing in your list, but should be on by default)

If I want to prevent remote root login at all what changes do I make (and how much more secure it is as compared to remote root login using SSH keys)?

Set PermitRootLogin no and AllowUsers otheruser.

If I prevent remote root login at all by making changes to sshd_config file, how will I ever be able to login as ROOT if I want to in future?

You will log in with your non-root user and use sudo to edit the configuration files and restart sshd.

Best Answer

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Ubuntu – meant by “no password set” for root account (and otthers)

Ubuntu – Disabling SSH password login for Ubuntu

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