Recently, I have tried a FreeBSD 7.4 i386 Install DVD just to take a look at some screens of FreeBSD on my Mac mini Intel 2006. After seeing several dialog screens, I was going to try the Live CD feature of FreeBSD, just to take a look at the contents of its harddisk on which Mac OS X Leopard is installed. And I did see them and later I ejected the FreeBSD Install DVD without changing anything on Mac mini's harddisk.
But after restart I found that Mac mini would not boot Mac OS X Leopard. Apparently, some code on FreeBSD DVD have tampered with someting on the Leopard harddisk.
When I checked the harddisk using another (and working) Leopard on a firewire connected harddisk
which is exactly the same with a working Mac OS X harddisk, except one section:
On a working Mac OS X harddisk, the first entry is "pmbr" , whereas it's "mbr" in my unworking OS X harddisk.
Furthermore I noticed that this unworking harddisk, though it shows 2 partitions in gpt, does not show up as ./disk0s1 ./disk0s2 under /dev, but it shows up simply as ./disk0
If only can I make it show up as ./disk0s1 ./disk0s2 under /dev, I think I can fix it. Is there a way to do it that way?
But after restart I found that Mac mini would not boot Mac OS X Leopard. Apparently, some code on FreeBSD DVD have tampered with someting on the Leopard harddisk.
When I checked the harddisk using another (and working) Leopard on a firewire connected harddisk
# gpt -r show disk0
returned this: 
which is exactly the same with a working Mac OS X harddisk, except one section:
On a working Mac OS X harddisk, the first entry is "pmbr" , whereas it's "mbr" in my unworking OS X harddisk.
Furthermore I noticed that this unworking harddisk, though it shows 2 partitions in gpt, does not show up as ./disk0s1 ./disk0s2 under /dev, but it shows up simply as ./disk0
If only can I make it show up as ./disk0s1 ./disk0s2 under /dev, I think I can fix it. Is there a way to do it that way?