Marshall Kirk McKusick (born January 19, 1954) is a computer scientist, known for his extensive work on BSD, from the 1980s to FreeBSD in the present day. He was president of the USENIX Association from 1990 to 1992 and again from 2002 to 2004, and still serves on the board. He is on the editorial board of ACM Queue Magazine. He is known to friends and colleagues as "Kirk".
McKusick is openly gay and lives in California with Eric Allman, who was his domestic partner since graduate school and whom he married in October, 2013. McKusick is an avid wine collector and the temperature and vital statistics of his house and wine cellar are available on the web from his homepage.
McKusick started with BSD by virtue of the fact that he shared an office at Berkeley with Bill Joy, who in essence spearheaded the beginnings of the BSD system.
Some of his largest contributions to BSD have been to the file system. He helped design the original Berkeley Fast File System (FFS). More recently, he implemented soft updates, an alternative approach to maintaining disk integrity after a crash or power outage, in FFS, and a revised version of UFS known as "UFS2". The magic number used in the UFS2 super block structure reflects McKusick's birth date: #define FS_UFS2_MAGIC 0x19540119 (as found in /usr/include/ufs/ffs/fs.h on FreeBSD systems).
He was also primarily responsible for creating the complementary features of filesystem snapshots and background fsck (file system check and repair), which both integrate closely with soft updates. After the filesystem snapshot, the filesystem can be brought up immediately after a power outage, and fsck can run as a background process.
The Design and Implementation series of books are regarded as very high quality works in computer science. They have been strongly influential in the development of the BSD descendants and have contributed to their cohesive and well-thought-out nature. The well-known daemon image, often used to identify BSD, is copyrighted by Marshall Kirk McKusick.
S. Leffler, M. McKusick, M. Karels, J. Quarterman: The Design and Implementation of the 4.3BSD UNIX Operating System, Addison-Wesley, January 1989, ISBN 0-201-06196-1. German translation published June 1990, ISBN 3-89319-239-5. Japanese translation published June 1991, ISBN 4-621-03607-6 (out of print).
S. Leffler, M. McKusick: The Design and Implementation of the 4.3BSD UNIX Operating System Answer Book, Addison-Wesley, April 1991, ISBN 0-201-54629-9. Japanese translation published January 1992, ISBN 4-8081-8039-5
M. McKusick, K. Bostic, M. Karels, J. Quarterman: The Design and Implementation of the 4.4BSD Operating System, Addison-Wesley, April 1996, ISBN 0-201-54979-4. French translation published 1997, International Thomson Publishing, Paris, France, ISBN 2-84180-142-X.