ERROR 1045 (28000): Access denied for user 'root'@'localhost'

[Sakai Noriko]

Hi everyone,
I understand that this question may have been discussed previously, but here my case seems just could get over by all the ways I found from previous posts.

OS: Ubuntu 16.04
DB: MySQL 5.1.15

After installed and started mysql service, I could not login with following commands:
mysql -u root -p
mysql -h localhost -u root -p

Following cures I found, I started 'mysqld_safe --user=root --skip-grant-tables &', and did following update to user table:

update user set authentication_string='mypassword'
where user='root'

flush privilegs

However after restarted the service, I still couldn't login with 'root' and kept getting following error:

ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

Could any one kindly point me to the direction to solve this?


Thanks