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Re: Tailing a series of log files

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On 6/14/2013 7:00 PM, Arved Sandstrom wrote:
> On 06/12/2013 09:04 AM, SamXiao wrote:
>> Hi all,
>>
>> I am working on a solution to keep track of a series of log files and
>> read the tail lines. At the very beginning, there is only one log file
>> named “TEST-YYYYMMDD-00.log” (where YYYYMMDD is the current date).
>> When the size of this log reaches to 10 MB, another log file
>> “TEST-YYYYMMDD-01.log” will be generated and so forth. After midnight
>> (12:00), a new log file with the next date starting with 00 again will
>> be generated.
>>
>> I know Apache Commons IO containing tail.java. However, seems it is
>> for tailing a single log file only. How could I keep tailing a series
>> of log files?
>>
>> Any help would be highly appreciated. Thanks.
>>
> For what it's worth, a sane logging system with a rollover policy has a
> base log file which always has the same name, like TEST.log. Decent text
> editors can follow a filename, UNIX command line "tail" doesn't follow a
> filename but rather the precise file in question. But point being, if
> you're looking to follow an "active" log file it may help if it's always
> got the same name. It's the rolled-over logs that have the suffixes.

     This is true, but I don't think it's going to help the
O.P. much.  Argument: The tailer (or any program) will use
the name to open the file, but subsequent accesses will use a
name-independent means -- "vnode," perhaps, or "handle."  If
the name-to-vnode/handle mapping changes after the program has
created its connection to the file, that's unlikely to affect
the existing connection: The program will, most likely, just
keep on tailing the original, oblivious to the name change.

     A tailer might, I suppose, open TEST.log anew for each
access: open, tail, close, pause, open, tail, close, pause,
and so on.  That approach would catch the renames, but would
also risk missing the last few lines of the pre-rename file:

	Tailer: open, tail, close, pause, open, tail, close, ...
	Writer: ... write ... write ... rename ... write ...
	Upshot:               ^^^^^
	               this batch isn't tailed

     If the log writer switches from file to file occasionally,
I think the only reliable approach is to have the log reader be
explicitly aware of the fact.

-- 
Eric Sosman
esosman@comcast-dot-net.invalid

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Thread

Tailing a series of log files SamXiao <foolsmart2005@gmail.com> - 2013-06-12 05:04 -0700
  Re: Tailing a series of log files Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-06-12 08:56 -0400
  Re: Tailing a series of log files Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-06-14 20:00 -0300
    Re: Tailing a series of log files Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-06-14 21:06 -0400
      Re: Tailing a series of log files Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2013-06-14 21:11 -0700
        Re: Tailing a series of log files Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-06-15 09:20 -0400
          Re: Tailing a series of log files JLP <JLP@jlp.com> - 2013-06-15 18:59 +0200
            Re: Tailing a series of log files JLP <JLP@jlp.com> - 2013-06-15 19:15 +0200
      Re: Tailing a series of log files Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-06-16 16:43 -0300

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