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Re: crontab and editors (was Re: Editor Priorities)

>>"Steve" == Steve Greenland <steveg@moregruel.net> writes:

 Steve> Crontab works like this roughly:

 Steve> 0. open /tmp/funnyname
 Steve> 1. copy existing /var/spool/cron/crontabs/whatever to /tmp/funnyname
 Steve> 2. start ($VISUAL|$EDITOR|/usr/bin/editor) on /tmp/funnyname,
 Steve>    wait for child to exit.
 Steve> 3. if stat.modtime(/tmp/funnyname) hasn't changed, then goto
 Steve>    7.

	Hmm. this could be a different inode from the one we had opened.

 Steve> 4. rewind(/tmp/funnyname)

	reopen, instead of rewind.

 Steve> 5. check that /tmp/funnyname parses
 Steve> 6. copy /tmp/funnyname /var/spool/cron/crontabs/whatever
 Steve> 7. rm /tmp/funnyname

 Steve> (All without closing /tmp/funnyname between 1 and 7).

	That is the bug. You are making assumptions about the
 environment that are not warranted, based on how some popular editors

 Steve> How is this broken - Other than in the presence of editors that do
 Steve> backups incorrectly. :-)

	The assumption that the inode has not changed is the breakage.
 I should have read the whole thread before posting (I thought there
 was a tmp race y'all were talking about), but this is still a problem
 with crontab. (incidentally, I just use crontab ~/etc/crontab, and thus I
 never noticed this bug).

 If someone says he will do something "without fail", he won't.
Manoj Srivastava   <srivasta@debian.org>  <http://www.debian.org/%7Esrivasta/>
1024R/C7261095 print CB D9 F4 12 68 07 E4 05  CC 2D 27 12 1D F5 E8 6E
1024D/BF24424C print 4966 F272 D093 B493 410B  924B 21BA DABB BF24 424C

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