Now, Nick, did your CD's md5sum come out ok?? Maybe I got some bad burns??...
Chris?? Your md5's??
Nick Rout wrote:
Volker, very very informative, thank you.On Tue, 11 Mar 2003 10:54:43 +1300 Volker Kuhlmann <[EMAIL PROTECTED]> wrote:If you cannot get an .iso image file on your hard drive to md5sum correctly after a couple of tries, it's pointless going on any further.True.Those silver SKC disks are obviously not of sufficient quality for use as stores for computer files. Sorry I didn't know that when I bought them.This may not be the real reason. The implementation of the isofs in Linux is quite bad (e.g. the method of making inodes will prevent hardlinked files from ever being stored properly on an isofs). The kernel also has the habit (ever since the first version) of reading too much data from the device, i.e. it reads past end of file on the disk. Needless to say this can cause I/O errors (oh what a surprise). For this reason only cdrecord has a -pad option, which simply writes additional zeros past the end of the filesystem onto the disk. Of course, this also stuffs your md5 sums. Another bug in the kernel is that it can't properly detect end-of-file on CD media. These additional zeros will screw your md5. For the record, all these are 100% identical: cat /dev/cdrom | md5sum md5sum < /dev/cdrom dd if=/dev/cdrom bs=2k | md5sum dd </dev/cdrom bs=2k | md5sum plus any more combinations everyone can think of. They either all work, or not at all. For current 2.4.18/2.4.19 kernels, they don't work reliably. Depending on how many blocks there are on the CD, reading will work, or fal with an I/O error (when the kernel tries to read past the end of the recorded bit stream on the media). Even if the read goes ok, unless you have happened to read precisely the correct number of bytes your md5 is screwed anyway. I have had kernels where cat /dev/cdrom resulted in a complete crash (kernel panick) right at the very end of reading. In my experience the only way to get reliable md5 sums with cds is to take matters into my own hands. Download the scriptutils package/tar from my web site and use writecd --blockread /dev/cdrom | md5sum or cook your own. The trick is dd bs=2k if=/dev/cdrom count=`isoinfo -i /dev/cdrom -d | awk ...` This will force reading of the correct number of blocks from the disk media (or any disk file). Note it will only work with an isofs on the CD, not with any other filesystem. Recently I got too fed up with this Linux isofs crap that I started to put ext2 onto the cds. Much easier and trouble free: create a 650MB or 700MB file filled with zeros (by reading from /dev/zero). Run mkfs -t ext2, don't forget -m0 as there really isn't any point in reserving blocks for the super user on a read-only filesystem. Loop-mount. Master your cd with cp, or rsync, or tar, or whatever, but no need to mess with mkisofs. Unmount. cdrecord file to cd, finished. Won't be readable by microsofties, but for my backups that's just as well. Volker -- Volker Kuhlmann is possibly list0570 with the domain in header http://volker.dnsalias.net/ Please do not CC list postings to me.-- Nick Rout Barrister & Solicitor Christchurch, NZ Ph +64 3 3798966 Fax + 64 3 3798853 http://www.rout.co.nz [EMAIL PROTECTED]
