What is password in R24.2.1?

I install R24.2.1 in my TX1. I can’t enter root user. I try to use nvidia,ubuntu as password, but all failed.

If you are trying to log in directly to root, then this doesn’t exist in Ubuntu. You’d use one of the forms of “sudo” to do this. You can unlock the root account, but normally this is discouraged (there are sometimes valid reasons to do this). So for example, single sudo use with “ls”:

sudo ls

Dropping into a root shell:

sudo -s

Full su to root:

sudo su -

If you really must unlock root, then you have to assign a password as well. Example:

sudo passwd root
# Now enter a password.

Unlock root:

sudo passwd -u root

You will perhaps need to take extra steps for ssh login to root, and often this is one of the security weaknesses. In cases where I do this I set ssh login for root as key only.

nvidia@tegra-ubuntu:/home/ubuntu/Downloads$ su -l
su: Authentication failure
nvidia@tegra-ubuntu:/home/ubuntu/Downloads$ su -l
su: Authentication failure

first password is nvidia,second password is ubuntu. All failed.
What is true password?

The default passwords are known by the entire world: “nvidia” for “nvidia”, “ubuntu” for “ubuntu”. If these fail, then one of these conditions exist:

  • The "sudo" command itself has the wrong permissions (improper flash from a non-Linux filesystem type can do this). What do you get from:
    ls -l /usr/bin/sudo

    (the suid root bit should be set)

  • Your Jetson is network accessible to a hostile network. Someone may have changed the passwords. You would never want to leave the default passwords if the network you are using is not controlled, e.g., a private router without random public WiFi is ok, but direct internet or sharing of a large router is bad.
  • You're running into a different issue and it isn't the password which is at fault.

Note that “su” is different from “sudo”. “su” won’t work on Ubuntu unless you’ve unlocked root login. This is not a password failure (even if the password is correct the command won’t be allowed on Ubuntu). “sudo” works because it is a regular user (in sudoers) assuming privileges and not a direct root login the way “su” is. If you want a root shell:

sudo -s

…sorry, that’s an “Ubuntu thing” (every Ubuntu install does this). Most Linux distributions don’t handle root login this way. Are you interested in unlocking root? Before doing so, make sure the other issues listed above are not a problem.