Single mode
 

Hi, can anybody say how to enter into single user mode to tresspass password for root. Thanks.

edit the grub boot entry (menu before kernel loads) and append S

init 1

Will drop you into single user mode. However, that would require you to already to already be logged in with root access.

Booting into single mode is different for each distributions. On RHEL, for example, at the boot screen, type

linux single

Check your distribution documentation on how to boot into single user mode