root crontab bug? (Undocumented find -mount option)

[Joe Smith]

In article <2802 at brchh104.bnr.ca> ray at kea.am.dsir.govt.nz (Ray Brownrigg) writes:
: What is this leading up to? Well I believe that an undocumented option to
: find will alleviate the problem. Certainly the "can't stat" message is no
: longer issued, and hopefully the hanging no longer occurs also.
: 
: The -mount option to find appears to restrict the activities of the
: command to the mounted partition(s) specified in the pathname-list. Thus
: the other common root crontab entry would be written something like:
: 
: 15 2 * * * find / /usr /home -mount -name core -atime +1 -exec rm {} \;

I have been using -xdev to prevent 'find' from going into mount points.
("-xdev" is documented in the man pages).  Therefore I was very curious
as to the difference between the -xdev and -mount options.
Here's what I found:

	% df
	Filesystem            kbytes    used   avail capacity  Mounted on
	/dev/sd0a               7855    3071    3998    43%    /
	/dev/sd0g             172117  142655   12250    92%    /usr
	/dev/sd0h             352909  288956   28662    91%    /export
	tardis:/var/spool/mail 61418   40105   15171    73%    /var/spool/mail
	tardis:/home/tardis   596610  519868   17081    97%    /home/tardis
	swap                   37424       0   37424     0%    /tmp
	% find / -xdev -print >temp.1
	% find / -mount -print >temp.2
	% diff temp.1 temp.2
	3,4d2
	< /export				4.2 mount point
	< /usr					4.2 mount point
	8d5
	< /home/tardis				nfs mount point
	252d248
	< /tmp					tmpfs mount point
	286d281
	< /var/spool/mail			nfs mount point

The end result is that -xdev tells 'find' to process mount points as if
the were empty directories.  (The directory is visible, but the files
inside it are not.)  The -mount option tells 'find' to completely ignore
any mount point not explicitly listed on the command line.  (The directory
is invisible.)
-- 
Joe Smith (408)922-6220 | SMTP: jms at tardis.tymnet.com or jms at gemini.tymnet.com
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