grub-setup: error: no mapping exists for `live-rw'

[holmes86]

hello,everyone!

I make a liveCD,and used grub2. I boot livecd ,and I found a problem.I executed "grub2-install /dev/sda" failure.and reported follwing error:
# grub2-install /dev/sda
grub-probe: error: no mapping exists for `live-rw'
Auto-detection of a filesystem module failed.
Please specify the module with the option `--modules' explicitly.

why need to detecting livecd root? I executed "/usr/sbin/grub2-setup --directory=/boot/grub2 --device-map=/boot/grub2/device.map /dev/sda" ,also reported as some error.
# /usr/sbin/grub2-setup --directory=/boot/grub2 --device-map=/boot/grub2/device.map /dev/sda
grub-setup: error: no mapping exists for `live-rw'

df -h command  results:
# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/mapper/live-rw    3096336   2004408   1060512  66% /
tmpfs                   516844        88    516756   1% /dev/shm
/dev/sr0                659160    659160         0 100% /mnt/live
varcacheyum             516844         0    516844   0% /var/cache/yum
/tmp                    516844        12    516832   1% /tmp
vartmp                  516844         0    516844   0% /var/tmp


who can help me? how should  I do it?
thanks very much!

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