Last command displays wrong information Post: 302544657

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Operating Systems Solaris Last command displays wrong information Post 302544657 by mcarpenter on Thursday 4th of August 2011 12:23:15 PM

08-04-2011

Registered User

Hi,

Author of the ckwtmpx program mentioned above here.

Quote:

wtmpfix does actually fix truncated entries too

This is correct. However there were a couple of things that I found sub-optimal:

1. wtmpfix(1M) is too aggressive. I have a test corrupt wtmpx file as "found in the wild" of 6.7M. Processing with wtmpfix discards 6.3M of data. ckwtmpx on the other hand discards 742 _bytes_ and the resulting file certainly appears valid (it processes correctly with last(1) or fwtmp(1M), no errors, no truncation).

wtmpfix's re-alignment jumps forward by one record plus however many bytes remain after removing a complete number of records from the file (the residue in the source quoted above). ckwtmpx's strategy is to crawl forward byte by byte.
ckwtmpx's strategy to check "does this look like a valid record?" is less complex (strict?). See is_record_valid() in ckwtmpx.c (apparently I can't yet post URLs...).

2. wtmpfix doesn't show what was discarded. I was interested in trying to work out where the corruption was coming from (ckwtmpx -e error_file). This didn't help. I know it isn't always lack of disk, and it isn't LARGEFILE (which I once suspected). The 742 byte example I quoted above contains (almost) two corrupt "system down" records with far too many NULL bytes.

Any problems with ckwtmpx, suggestions, patches, please hit me by email, mcarpenter@free.fr. Thanks!

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LEARN ABOUT DEBIAN

seqdiag

SEQDIAG(1)						      General Commands Manual							SEQDIAG(1)

NAME

       seqdiag - generate sequence-diagram image file from spec-text file.

SYNOPSIS

       seqdiag [options] file

DESCRIPTION

       This manual page documents briefly the seqdiag commands.

       seqdiag is generate sequence-diagram image file from spec-text file.

OPTIONS

       These  programs	follow	the  usual  GNU  command  line	syntax, with long options starting with two dashes (`-').  A summary of options is
       included below.	For a complete description, see the Info files.

       --version
	      show program's version number and exit

       -h, --help
	      show this help message and exit

       -a, --antialias
	      Pass diagram image to anti-alias filter

       -c FILE, --config=FILE
	      read configurations from FILE

       -o FILE
	      write diagram to FILE

       -f FONT, --font=FONT
	      use FONT to draw diagram

       -T TYPE
	      Output diagram as TYPE format

SEE ALSO


       The programs are documented fully by
       http://tk0miya.bitbucket.org/seqdiag/build/html/index.html

AUTHOR

       seqdiag was written by Takeshi Komiya <i.tkomiya@gmail.com>

       This manual page was written by Kouhei Maeda <mkouhei@palmtb.net>, for the Debian project (and may be used by others).

								   May 21, 2011 							SEQDIAG(1)

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