--- psinib.pl	2003/01/04 11:42:56	1.1
+++ psinib.pl	2003/01/04 13:29:12	1.3
@@ -21,6 +21,7 @@
 use List::Compare;
 use Filesys::SmbClient;
 #use Taint;
+use Fcntl qw(LOCK_EX LOCK_NB);
 
 # configuration
 my $LOG_TIME_FMT = '%Y-%m-%d %H:%M:%S';	# strftime format for logfile
@@ -39,6 +40,18 @@
 open(L, "> $LOG") || die "can't open log $LOG: $!";
 select((select(L), $|=1)[0]);	# flush output
 
+# make a lock on logfile
+
+my $c = 0;
+{
+	flock L, LOCK_EX | LOCK_NB and last;
+	sleep 1;
+	redo if ++$c < 10;
+	# no response for 10 sec, bail out
+	print STDERR "can't take lock on $LOG -- another $0 running?\n";
+	exit 1;
+}
+
 # taint path: nmblookup should be there!
 $ENV{'PATH'} = "/usr/bin:/bin";
 
@@ -426,5 +439,92 @@
 	xlog($share,"backup completed...");
 }
 
+__END__
 #-------------------------------------------------------------------------
 
+
+=head1 NAME
+
+psinib - Perl Snapshot Is Not Incremental Backup
+
+=head1 SYNOPSIS
+
+./psinib.pl
+
+=head1 DESCRIPTION
+
+This script in current version support just backup of Samba (or Micro$oft
+Winblowz) shares to central disk space. Central disk space is organized in
+multiple directories named after:
+
+=over 4
+
+=item *
+server which is sharing files to be backed up
+
+=item *
+name of share on server
+
+=item *
+dated directory named like standard ISO date format (YYYYMMDD).
+
+=back
+
+In each dated directory you will find I<snapshot> of all files on
+exported share on that particular date.
+
+You can also use symlink I<latest> which will lead you to
+last completed backup. After that you can use some other backup
+software to transfer I<snapshot> to tape, CD-ROM or some other media.
+
+=head2 Design considerations
+
+Since taking of share snapshot every day requires a lot of disk space and
+network bandwidth, B<psinib> uses several techniques to keep disk usage and
+network traffic at acceptable level:
+
+=over 3
+
+=item - usage of hard-links to provide same files in each snapshot (as opposed
+to have multiple copies of same file)
+
+=item - usage of file size, atime and mtime to find changes of files without
+transferring whole file over network (just share browsing is transfered
+over network)
+
+=item - usage of C<.md5sum> files (compatible with command-line utility
+C<md5sum> to keep file between snapshots hard-linked
+
+=back
+
+=head1 CONFIGURATION
+
+This section is not yet written.
+
+=head1 BUGS and LIMITATIONS
+
+There is not real reason why you can't take snapshot more often than
+one a day. Actually, if you are using B<psinib> to backup Windows workstations
+they tend to come-and-go, so running B<psinib> several times a day
+increases your chance of having up-to-date backup (B<psinib> will not
+make multiple backups for same day if such backup already exists).
+
+However, changing that to produce backups which are, for example, hourly
+is a simple change of C<$DIR_TIME_FMT> which is currently set to
+C<'%Y%m%d'> (see I<strftime> documentation for explanation of that 
+format). If you change that to C<'%Y%m%d-%H> you can have hourly snapshots
+(if your network is fast enough, that is...). Also, some of messages in
+program will sound strange, but other than that it should work.
+I<You have been warned>.
+
+=head1 AUTHOR
+
+Dobrica Pavlinusic <dpavlin@rot13.org>
+
+L<http://www.rot13.org/~dpavlin/>
+
+=head1 LICENSE
+
+This product is licensed under GNU Public License (GPL) v2 or later.
+
+=cut