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Physical access
From dankwiki
So you've got physical access to a UNIX box. How do you get root access?
Removing root password
This requires that the filesystem containing /etc is not encrypted. Remove the disk with the filesystem containing /etc, and mount it on another machine.
- Edit /etc/passwd, and remove the second field for the root entry:
root::0:0:root:/root:/bin/bash
- Edit /etc/shadow, and do the same:
root::18242:0:99999:7:::
- If you intend to set a new root password using passwd, it's recommended to add an 'x' back to the /etc/passwd, so that /etc/shadow is used again:
root:x:0:0:root:/root:/bin/bash