i386/121124: FreeBSD 6.3 installation deletes MBR partition

[Dan Strick]

>Number:         121124
>Category:       i386
>Synopsis:       FreeBSD 6.3 installation deletes MBR partition
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    freebsd-i386
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue Feb 26 17:40:00 UTC 2008
>Closed-Date:
>Last-Modified:
>Originator:     Dan Strick
>Release:        FreeBSD 6.3-RELEASE i386
>Organization:
none
>Environment:
System: FreeBSD mist.nodomain 6.3-RELEASE FreeBSD 6.3-RELEASE #0: Sun Feb 24 23:23:03 PST 2008 root at mist.nodomain:/usr/src/sys/i386/compile/MIST i386
>Description:
This was the MBR partition table for disk ad0 before I booted the
release 6.3 installation cd disk 1:

        The data for partition 1 is:
        sysid 11 (0x0b),(DOS or Windows 95 with 32 bit FAT)
            start 63, size 8209152 (4008 Meg), flag 0
                beg: cyl 0/ head 1/ sector 1;
                end: cyl 510/ head 254/ sector 63
        The data for partition 2 is:
        sysid 99 (0x63),(System V/386 (such as ISC UNIX), GNU HURD or Mach)
            start 8209214, size 1 (0 Meg), flag 0
                beg: cyl 510/ head 254/ sector 63;
                end: cyl 510/ head 254/ sector 63
        The data for partition 3 is:
        sysid 165 (0xa5),(FreeBSD/NetBSD/386BSD)
            start 8209215, size 8225280 (4016 Meg), flag 80 (active)
                beg: cyl 511/ head 0/ sector 1;
                end: cyl 1022/ head 254/ sector 63
        The data for partition 4 is:
        sysid 165 (0xa5),(FreeBSD/NetBSD/386BSD)
            start 16434495, size 143637165 (70135 Meg), flag 0
                beg: cyl 1023/ head 0/ sector 1;
                end: cyl 1023/ head 254/ sector 63

When I selected disk ad0 under the sysinstall partition menu it popped up
this warning message:

			Disk slicing warning:
	chunk 'ad0s2' [8209214..8209214] does not start on a track boundary

and showed this information when it entered the FDISK partition editor:

  Disk name:      ad0                                    FDISK Partition Editor
  DISK Geometry:  9964 cyls/255 heads/63 sectors = 160071660 sectors (78159MB)

  Offset       Size(ST)        End     Name  PType       Desc  Subtype    Flags

           0    8209214    8209213        -     12     unused        0          
     8209214          1    8209214    ad0s2      4    unknown       99
     8209215    8225280   16434494    ad0s3      8    freebsd      165
    16434495  143637165  160071659    ad0s4      8    freebsd      165
   160071660      12755  160084414        -     12     unused        0

I exited the partition editor without changing any partitions but I did
request installation of the usual FreeBSD boot manager (menu option BootMgr)
in the next menu.

After the installation was over I discovered that the first partition,
Windows XP, was now <UNUSED>.  The other partitions were unmodified.

>How-To-Repeat:

	Create a similar MBR partition table on some disk, run sysinstall
	and select that disk under the

		3 Partition      Allocate disk space for FreeBSD

	menu item in the "Choose Custom Installation Options" menu.
	This also works if you run sysinstall from inside FreeBSD.

>Fix:

	Work around:  manually edit the MBR partition table with fdisk
	from FreeBSD after the installation is complete.  Of course we
	saved a backup copy of the MBR before we began the FreeBSD
	installion.  Doesn't everybody?  :-)

	I used to think that only MS Windows installations callously
	destroyed competing OS partions.  Now FreeBSD joins the club.
	:-)
>Release-Note:
>Audit-Trail:
>Unformatted: