chntpw is a software utility for resetting or blanking local passwords used by Windows NT operating systems on Linux.

It does this by editing the SAM database where Windows stores password hashes.

There are two ways to use the program: via the standalone chntpw utility installed as a package available in most modern Linux distributions (e.g. Ubuntu[1]) or via a bootable CD/USB image.

chntpw has no support for fully encrypted NTFS partitions (the only possible exceptions to this are encrypted partitions readable by Linux such as LUKS), usernames containing Unicode characters, or Active Directory passwords (with the exception of local users of systems that are members of an AD domain).

[2] The chntpw utility is included in many various Linux distributions, including ones focused on security: For the software's 10th anniversary, the author changed the license from a non-commercial one to the GNU General Public License (GPL) Version 2.