When I login, system accepts my password to use system. But, when I try to update software programs, system says "manipulation error" or something like that.
Went to login screen with Ubuntu recovery mode and tried to reset password using mount -re, etc but says password unchanged. What am I doing wrong?
I found this and it worked for me:
How to reset your root / admin password in Ubuntu:
(It may not work in 12.10 if you have used full disk encryption)
Instructions:
Reboot to the Grub Menu. (Hold down Left-Shift Key if you have a single boot system)
Choose Recovery Mode
Select Root -- Drop to root shell prompt
mount -o rw,remount /
ls /home
passwd username
reboot
To test out new password:
su username
sudo su
reboot
