Hi, I have been having a number of problems dealing with time zones and synchronising files using Rsync to my linux machine on Cygwin with Windows XP. I have read discussions previously on these mailing lists on how there are problems that occur when there is a change in daylight savings time.
I saw a page by http://optics.ph.unimelb.edu.au/help/rsync/rsync_pc1.html that discussed how to set the timezone to UTC and then do an ls to see if the file dates are really the same. If there is a DST problem the suggestion was to set --modify-window=3601 to set a 1 hour fuzzy factor to prevent the problem. I had the same problem but didn't want to set this flag since I was worried I would miss important updates on some files that had changed shortly after an rsync run. I did a lot of reading around about this and in this email I have developed a solution to the problem that I have not seen anywhere else. My solution is for WinXP with FAT filesystem but I am not sure what the effect is with NTFS disks. From what I read up, FAT stores its dates in local time and not in GMT. So it uses an offset from the clock settings to calculate the GMT value to report to Rsync. The problem is that these DST calculations have a bug in that if your clock moves over a DST boundary then files created on the "other side" of the bounday will mysteriously get a 1 hour offset applied. Unix avoids this problem by having proper DST calculations but Windows doesn't do this right. The references below contain some discussions about how these are calculated. In Adelaide where I live, we left Daylight Savings Time at the end of March, and so now my files are all 3600 seconds off relative to my Linux box. The files were synchronised while DST is in effect. Now DST is off I need to do something about this, I don't really want to resync 20 Gb of data over SSH. If you run a 'stat' program over the files in question, the seconds since 1970 value will be off by 3600. If you change the time zone nothing seems to change and the 1970 values on the Windows box remain the same. FAT is supposed to use the time zone offset to calculate the GMT time but it doesn't seem to take effect. You have to reboot the box! For some reason parts of the TZ settings affect Windows immediately and others don't kick in until many minutes later, so I just reboot to be safe - I spent half a day to discover this, so it is important! So all we need to do is get a time zone which is one hour away from where we are now and it should apply a 1 hour offset to all the GMT values and then this will fix our problem. I live in Adelaide which is GMT+9:30 normally, so I need GMT+10:30. There is no time zone like this so we need to hack the time zone files that Windows uses instead. I downloaded a tool from Microsoft called TZEDIT.EXE that comes with some versions of Windows resource kit. Using this tool, you can edit the time zone settings for the current area you are in. I created a new time zone based on my previous Adelaide one called "Cygwin Hacked" with GMT+10:30 and daylight savings disabled. Now after doing this you *MUST* activate the time zone change properly. Make the change using TZEDIT, then you need to go to the control panel time/date tool and click on the time zone and hit ok to make it take effect. You can't enable the time zone and then edit it, you have to do it in the right order. Then you must reboot the machine to make it take effect. (It may have a delay to take effect but I don't know how long it is and I'm too lazy to wait all day) Now after the box reboots you will be in GMT+10:30 and when you run Rsync everything just works like a dream, just like it did a week ago before DST finished. You do not need to use --modify-window which could potentially introduce errors and everything just works very well now. In hindsight this problem could have been simplified if I had done the first rsync when DST was not on. So if during July (I am in the southern hemisphere) I did the rsync, then I could have just unticked the "support DST" box in the clock control panel and could have avoided these problems. Unfortunately because my backup was done when DST was enabled I have to now create a time zone that simulates DST. For now this is my fix for the problem but I am not sure if there are any other effects that I am not aware of. Everything seems to be working fine. Here are some references that I collected while researching this problem. They contain a lot of information about the ways that Windows deals with timestamps on NTFS and FAT filesystems. http://optics.ph.unimelb.edu.au/help/rsync/rsync_pc1.html http://list-archive.xemacs.org/xemacs-nt/199911/msg00130.html http://sources.redhat.com/ml/cygwin/2002-12/msg01065.html http://p2p.wrox.com/archive/c_plus_plus_programming/2001-06/53.asp http://www.codeproject.com/datetime/dstbugs.asp http://lists.samba.org/pipermail/rsync/2000-July/002491.html http://support.microsoft.com/default.aspx?scid=kb;[LN];158588 http://www.cygwin.com/ml/cygwin/2000-06/msg00810.html Here is the source code for a short program I wrote to find out what the modified time of a file is, it is important that we print out the seconds since 1970 GMT because this is the value that Rsync uses to determine if it needs to copy the file over. I use this tool because it shows the seconds values and is invariant to the use of the TZ environment variable and other problems that can crop up. #include <stdio.h> #include <sys/stat.h> #include <unistd.h> void main (int argc, char *argv[]) { struct stat buf; if (argc != 2) exit (1); stat (argv[1], &buf); printf ("file %s\n", argv[1]); printf ("atime = %d %s", buf.st_atime, ctime (&buf.st_atime)); printf ("mtime = %d %s", buf.st_mtime, ctime (&buf.st_mtime)); printf ("ctime = %d %s", buf.st_ctime, ctime (&buf.st_ctime)); } Sorry for writing such a long email. This has been bugging me for ages and each time DST kicks in it throws my backup system into chaos. I found pieces of information all over the web but nothing really proposed a proper solution to the problem so I wanted to put this all in one place so people can find it in the future. regards, Wayne ---------------------------------------------------------------------------- Wayne Piekarski - PhD Researcher / Lecturer pho: +61-8-8302-3669 fax: +61-8-8302-3381 Tinmith Project - Wearable Computer Lab mob: 0407-395-889 Advanced Computing Research Centre ema: [EMAIL PROTECTED] University of South Australia www: http://www.tinmith.net -- Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple Bug reporting: http://cygwin.com/bugs.html Documentation: http://cygwin.com/docs.html FAQ: http://cygwin.com/faq/
