bin/54492: tail -F duplicates lines
Colin Percival
cperciva at daemonology.net
Tue Jul 15 00:10:19 PDT 2003
>Number: 54492
>Category: bin
>Synopsis: tail -F duplicates lines
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Tue Jul 15 00:10:17 PDT 2003
>Closed-Date:
>Last-Modified:
>Originator: Colin Percival
>Release: FreeBSD 4.7-SECURITY
>Organization:
>Environment:
>Description:
tail -F sometimes duplicates lines after the first rotation.
>How-To-Repeat:
cperciva at beastie$ rm foo && touch foo && ( for x in 1 2 3 4 5; do echo
hello $x > foo && sleep 2 && echo world $x >> foo;done & tail -F foo )
hello 1
world 1
hello 2
hello 2 # this line shouldn't be here
world 2
hello 3
hello 3 # this line shouldn't be here
world 3
hello 4
hello 4 # this line shouldn't be here
world 4
hello 5
hello 5 # this line shouldn't be here
world 5
I've also observed this when using `tail -F` on Apache logfiles (again,
after the file has been rotated once; when that happens, it prints out
all the lines in the file again, as if the file had been rotated).
>Fix:
Based on the symptoms, I'd say it looks like a bug in either the
rotation-detection or the truncation-detection code; but I'm not familiar
enough with kqueue to say any more than that.
>Release-Note:
>Audit-Trail:
>Unformatted:
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