Changes to the 'find' utility in UNICOS 9

by Tom Parker

For POSIX compliance, the find(1) utility calculates time differently beginning with the UNICOS 9.0 release. You should verify scripts that use the find utility; to achieve the desired results, you may have to rewrite some scripts.
The change affects the -atime, -ctime, and -mtime primaries. The meaning of the numeric argument n to these primaries changed in the following two ways:

In UNICOS 8.0 and earlier, n is day units (0 equals the 24 hours since the last midnight). In UNICOS 9.0 and later, n is 24-hour blocks starting with the current time (0 equals the 24-hour block that begins now).

In UNICOS 8.0 and earlier, - is time after the end of the 24-hour block and + is time before the start of the 24-hour block. In UNICOS 9.0 and later, + and - refer to the same one-second starting point in time.
Therefore, the find utility now calculates starting points in 24-hour increments from the current time (that is, from now, the current second) rather than from the 24-hour block that started at last midnight. A starting point equals the current time minus 86,400 seconds (the number of seconds in 24 hours) times n. The period defined by n is as follows:

n: Starting point to the starting point plus 1 day (or, the 24-hour period that begins at n)

+n: Any time before (earlier than) the starting point (that is, older than n)

-n: Any time after (later than) the starting point (that is, younger than n)

The effects of the first change are illustrated in the following example:
     find . -mtime +0
In UNICOS 8.0 and earlier releases, this command finds any files in the current directory and its subdirectories that are older than last midnight. Some administrators use this as part of a command or script to remove day-old files from /tmp. Conversely, beginning with UNICOS 9.0, this command finds all files older than now (that is, it finds anything older than 24n hours, and because n is 0, it finds all files older than now).
In UNICOS 9.0, to find all files that are older than 24 hours, use the following command:
   find . -mtime +1
The effects of the second change are illustrated in the following command-sequence example:
   find . -mtime +1 -print
   find . -mtime  1 -print
   find . -mtime -1 -print
In UNICOS 8.0 and earlier releases, these three commands produce mutually exclusive listings, which together include any and all files. Beginning with UNICOS 9.0, the second command produces a listing that is almost entirely included in the listing produced by the third command.
In summary, to avoid unexpected results when using the POSIX-compliant find utility, you should verify any scripts that use the find utility with the -atime, -ctime, and -mtime primaries, and you should be aware of these changes in behavior when you invoke the find utility at the command line with these primaries.
Note also, that -print now seems to be the default.

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