Josh Work U-Michigan MTS Anecdotes Change Log

3:15pm 16 November 1989
Problems with the file system, notably $PERMIT and $FILESTATUS, on every system that uses MTS, made emergency reloads a requirement. The UB system was reloaded at 1:53pm and the UM system at 1:25pm.
4:47pm 16 November 1989
More information from the systems staff:

The down-time on the UM and UB systems was due to a bug that was exposed at midnight of November 16, 1989, which was the 32768th day after Mar 1, 1900. The file system uses halfwords to store the number of days since Mar. 1, 1900 for lastref, lastcat, and credat.

A halfword can be used to store values from -32768 to 32767. or from 0 to 65535. Parts of the system assumed the first value range, which caused various other parts of the system to PGNT, or use an incorrect value for evaluating how old a file is. This caused the $PERMIT PGNT, and the problems with HASPLOG and CMDSTAT. $FILESTATUS and $DUPLICATE also suffered from this bug.

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