On Wed, Sep 18, 2002 at 12:53:39AM +0530, Raghavendra Bhat wrote: > Vineet Kumar: > > >> If it doesn't, then think about digging deeper to find out what differs > > I have had downloaded the ISO images and the checksums match. A small doubt > though, I can burn CD-Rs using these images without any hitch. But when I do a > `dd' of the resultant CD/s, the generated image md5sum differs from the original > md5sum of the downloaded ISO. Why is it so ? Is it due to control > data/something else being added to the CD during the `cdrecord' burn process ?
The ISO images are rarely the exact size of the media on which you burn them. In order to use dd with md5sum on a CD burned from the images in such a way to reproduce the md5sum of the image file, you have to direct the dd program to read exactly the same number of bytes from the CD as is in the image file. It tends to work better for me if I read the bytes from the CD in large chunks, I've found. So, I'll use the bs= and count= arguments to dd to do this. bs x count = total number of bytes in image file Using as an example this old ISO image I have sitting around: $ ls -ld /opt/iso/Debian/debiani386-2.2-1.iso -rw-r--r-- 1 root root 658933760 Oct 8 2000 /opt/iso/Debian/debiani386-2.2-1.iso I calculate how many 1024byte blocks it is using 'dc': $ echo " 4 k 65893376 1024 / p" | dc 64349.0000 So, having burned that image to a disk in my CD-RW drive, I can check its md5sum this way: $ dd if=/dev/scd0 count=64349 bs=1024 | md5sum The result of this should be the same as running: $ md5sum debiani386-2.2-1.iso I tend to write the size of the iso image on my CD-R labels, along with several digits of the md5 checksum, so that I can check their integrity this way. --Joe -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
