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FreeBSD CDROMs - Checking The Media

Suspect a CDROM Media Error ? - First Check The MD5 Checksum Of Your Cdrom

• If you have a problem installing from cdrom, or accessing a file off cdrom, you might be suspicious of the data integrity on your media, if so :
  • It is Not necessary, to re-fetch & compare the entire 650 Meg .iso file, unless your md5 check (below) fails. Re- downloading before doing an md5 check would just be a foolish waste of internet resources - even if your download `pipe' is wide/fast, & you can afford it, you'd still be depriving others of limited Internet bandwidth on the servers.
  • You do Not need to reinstall everything just to check the CDROM data consistency. That would be a foolish thing to do !
• You can can easily check for CDROM media/ data errors like this:
  • Prepare to copy the CDROM image to hard disk (as FreeBSD will not run md5 on a 2K CDROM block device).
  • Find a modern Unix that has the md5 command.
  • Find space for a 650 Meg temporary file - perhaps /tmp or /usr/tmp or /usr1/tmp or ~/tmp maybe. Type "df& "mount" " to see what space is available where.
  • Ascertain correct CDROM image size & expected MD5 checksum by either:
    
    
    • For VSL CDROMs produced by JHS, Look at the bottom of the paper label, or the label on this web page where it says EG

      Size: 639729664  MD5:6b205e3c2e72c90c2e0718da47b26540
      

    • For Generic FreeBSD ISO images, look here:

      ftp ftp.de.freebsd.org ( Or ftp.freebsd.org )
      cd pub/FreeBSD/ISO-IMAGES-i386/4.9
      dir
      dir 4.9-disc1.iso
      get CHECKSUM.MD5 
      bye
      cat CHECKSUM.MD5
      

  • Learn name of your cdrom device driver. (Typically /dev/cd0a or /dev/acd0a) To discover device name of your cdrom, Try one of these:
    • mount /cdrom ; mount | grep cdrom ; umount /cdrom
    • dmesg | more
    • /stand/sysinstall - and add a cdrom
  • Calculate block count from byte size (shown by "dir" above), divide by 2048 bytes / block. count= is not always necessary, but it prevents problems with some cdrom drivers that return 1 block (2048 bytes) too many, which would make md5 later falsely report an error.
  • Start (& wait a while) for

    dd if=/dev/cd0a bs=2k count=`dc -e "639729664 2048 / p"` of=/usr/tmp/650Meg_file
    md5 /usr/tmp/650Meg_file 
    rm /usr/tmp/650Meg_file
    

    & the resulting MD5 checksums should agree.
    
• The above is the best way to conclusively prove if a CDROM containing a FreeBSD distribution image has corrupted data, or if there is any optical incompatibility between my CDROM writer, the CDROM media, & your CDROM reader.

What Not To Do

• Telling me you see bad checksums on individual packages, or failure to install particular bits is near impossible or too time consuming for me to investigate, without access to your hardware & configuration & install sequence, & doesn't interest me at least until you first assure yourself & me that your hardware verifies the md5 is correct & detects no CDROM distribution media error.
• Package errors could (though unlikely) come from FreeBSD package build errors (for which generic FreeBSD would be at fault, not sender's CDROM writer, at which point you should contact FreeBSD.Org, not me).
• More likely, recipient's cdrom drive may have intermittent dirty optics (ie loose dust/fluff), media may be dirty, or RAM error, CPU heat etc error, power supply error, hard disc error, bad contacts, human error etc.

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