Help! I've forgotten my master password to my imac.

Question

I was recently going through a divorce, and had stored my entire household in a storage unit, including my iMac. Now I can't remember the Master password. Can anyone tell me how to reset it, PLEASE? Thanks so much!

Answer 1

Classic operating system passwords, which refer to passwords on 13 + year old operating systems are much different in setting.
You should at minimum be able to find your Darwin version if running some version of Mac OS X by booting with command-S on a wired USB keyboard.
That should help tell us your Mac OS X version.  This table comes from: http://en.wikipedia.org/wiki/Darwin_(operating_system)
Version
Date
Corresponding releases
Notes
0.1
March 16, 1999
Mac OS X DP
0.1 is contrived (for sorting and identification) as this identified itself simply as Mac OS 10.0
0.2
November 10, 1999
Mac OS X DP2
1.0
February 2000
Mac OS X DP3
1.1
April 5, 2000
Mac OS X DP4
1.2.1
November 15, 2000
Mac OS X Public Beta
Code named "Kodiak"
1.3.1
April 13, 2001
Mac OS X v10.0
First commercial release of Darwin
1.3.1
June 21, 2001
Mac OS X v10.0.4
All releases of "Cheetah" (10.0–10.0.4) had the same version of Darwin
1.4.1
October 2, 2001
Mac OS X v10.1
Performance improvements to "boot time, real-time threads, thread management, cache flushing, and preemption handling," support for SMB network file system, Wget replaced with cURL.[15]
5.1
November 12, 2001
Mac OS X v10.1.1
Change in numbering scheme to match Mac OS X build numbering scheme (e.g., Mac OS X v10.1 contains build numbers starting with 5 so Mac OS X v10.1.1 is now based on Darwin 5.1; i.e., 10.1 means 5 so 10.1.1 means 5.1, etc.)
5.5
June 5, 2002
Mac OS X v10.1.5
Last release of "Puma"
6.0.1
September 23, 2002
Mac OS X v10.2(Darwin 6.0.2)
GCC upgraded from 2 to 3.1, IPv6 and IPSec support, mDNSResponder service discovery daemon (Rendezvous), addition of CUPS, Ruby, and Python, journaling support in HFS+ (Darwin 6.2), application profiles ("pre-heat files") for faster program launching.[16]
6.8
October 3, 2003
Mac OS X v10.2.8
Last release of "Jaguar"
7.0
October 24, 2003
Mac OS X v10.3
BSD layer synchronized with FreeBSD 5, automatic file defragmentation, hot-file clustering, and optional case sensitivity in HFS+, bash instead of tcsh as default shell, read-only NTFS support (Darwin 7.9).[17]
7.9
April 15, 2005
Mac OS X v10.3.9
Last release of "Panther"
8.0
April 29, 2005
Mac OS X v10.4
Mac OS X forApple TV(Darwin 8.8.2)
Stable kernel programming interface, finer-grained kernel locking, 64-bit BSD layer, launchd service managementframework, extended file attributes, access control lists, commands such as cp and mv updated to preserve extended attributes and resource forks.[18]
8.11
November 14, 2007
Mac OS X v10.4.11
Last release of "Tiger"
9.0
October 26, 2007
iPhone OS 1(Darwin 9.0.0d1)
Mac OS X v10.5
Full POSIX compliance, improved hierarchical process scheduling model, dynamically allocated swap files, dynamic resource limits (for files and processes), process sandboxing, address space layout randomization, DTrace tracingframework, file system events daemon, directory hard links, Apache 1.3 and PHP 4 updated to Apache 2.2 and PHP 5, read-only ZFS support.[19]
9.8
August 5, 2009
Mac OS X v10.5.8
Last release of "Leopard"
10.0
August 28, 2009
Mac OS X v10.6
iOS 4
End of official support for PowerPC architecture (although several fat binaries, such as Kernel, still contain PPC images); 64-bit kernel and drivers, libdispatch task parallelization framework, OpenCL heterogeneous computingframework, support for blocks in C, transparent file compression in HFS+.[20]
10.8
June 23, 2011
Mac OS X v10.6.8
Last release of "Snow Leopard"
11.0.0
July 20, 2011
Mac OS X v10.7iOS 5[21]
XNU no longer supports PPC binaries (fat binary only for i386, x86_64). XNU requires an x86_64 processor. Improved sandboxing of applications
11.4.2
October 4, 2012
Mac OS X v10.7.5
Last release of "Lion", supplemental
12.0.0
February 16, 2012
OS X v10.8
Code named "Mountain Lion"; the word "Mac" has been dropped from the name
12.5.0
September 12, 2013
OS X v10.8.5
Last release of "Mountain Lion"
13.0.0
June 11, 2013
iOS 7 and OS X v10.9
If you are indeed running a Classic operating system, here's how to reset your password:
Mac OS 9.1 - forgot password - reset
Here's how to reset your password with Apple Article to reset the password for OS X 10.6.8 and earlier, and 10.7 and later.
Note: Macs can't boot an operating system older than shipped with them, or a different Mac model or different version of the same Mac model's installer disc.  They can use newer retail discs as long as they meet specs.   Lastly no discs were included for Mac OS X 10.7 or later.