As of right now, I create a brand new Google virtual machine. I upgraded the OS from Debian 9 (Jessie) to Debian 10 (Buster). For whatever reason, I cannot use superuser. Whenever I try, I get the error: su: Permission denied. The file permissions for /bin/su are

-rwsr-xr-x 1 root root 63K Jan 10 2019 su

The groups my user (Lunar) is in, are:

root sudo developers lunar

I also tried doing sudo adduser lunar wheel, although the group did not exist beforehand, and is not appearing in the groups above. I am SSH-ing into the computer, and I've tried the commands:

su -
su root

Each above the above commands have been executed with and without sudo. Any suggestions?

Edit: After further testing, I cannot su into ANY user, including my own account.

  • Check with strace what file it doesn't have permission to read.
    – arved
    Jul 24, 2019 at 15:04
  • 1
    With su you need to use the target user's password. For root accounts this means that someone has to have set the root account at some point, and on more modern systems that's not always the case
    – roaima
    Nov 26, 2021 at 11:07

1 Answer 1


I've never heard of this happening with Debian 10, but somethimes with macOS you have to run

sudo -i

to get it to work, because your root account probably doesn’t have a password. With sudo, as long as you are in the sudo group, you can use your own password.

  • 1
    @roaima that’s true, back when I wrote this I didn’t know about sudo -i. I have changed by answer. Nov 27, 2021 at 13:52

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