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I compiled a new kernel(3.2) and I have it running on an ARM board. I wanted to enable some params on the /proc directories. Therefore I have to be logged in as root. Hence I did the following on my newly compiled system:

sudo passwd su

and set a new root password.

Then I logged in as root. However I get the error message su-Authentication failure.

How do I solve this problem? Has this to do with the /usr/bin file permissions?

What setting should I change to be able to login as root?

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Then I logged in as root. However I get su-Authentication failure error message., were you doing root login or su login? – warl0ck Sep 28 '12 at 12:42
Why are you trying to change the password? You can't sudo su -? – Mat Sep 28 '12 at 13:07
Oops that really was a typo! I had done only sudo passwd root... – user489152 Oct 1 '12 at 11:10

the argument passwd takes is a username

sudo passwd root

if that doesn't work you should reboot into single user mode and change the password that way

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could you please explain how I can reboot into this mode? although I reset the password SUCCESSFULLY, I cannot login as root with the new password. Please help – user489152 Oct 1 '12 at 11:12
assuming you're using grub:to reboot into single user mode you reboot the machine and when the GRUB boot loader comes up you need to edit the command line to load the kernel and append a 1 after all the arguments – h3rrmiller Oct 1 '12 at 11:54
I fixed it. I had to set the sticky bit of the su binary! So when I did chmod +s /bin/su, I could "su" with the changed root password.Thanks for all your help – user489152 Oct 1 '12 at 14:45
you could've also used sudo -i to gain root via sudo without elevating with su – h3rrmiller Oct 1 '12 at 15:46

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