Hi, all
In CentOS 5.5 ,  value of BASH_VERSINFO[5]/MACHTYPE  is "x86_64-redhat-linux-gnu"(bash-3.2-32.el5.x86_64)
However,  "x86_64-unknown-linux-gnu" in CentOS 6.0/cr (bash-4.1.2-8.el6-x86_64)

# cat /proc/cpuinfo
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 23
model name      : Intel(R) Xeon(R) CPU           X3330  @ 2.66GHz
...

ps:  "x86_64-redhat-linux-gnu" in rhel 6.1(bash-4.1.2-8.el6-x86_64)