Why can't i mount a ramdisk in ep2c35 DEV board

I have run the Linux .But I want to use the ramdisk. i find i can't mount

# dd if=/ramfs.img of=/dev/ram0

dd if=/ramfs.img of=/dev/ram0

6+1 records in

6+1 records out# mount /dev/ram0 /mnt/ide0

mount /dev/ram0 /mnt/ide0

can't create lock file /etc/mtab~31: Read-only file system (use -n flag to overr

ide)

when i type the next command

# dd if=/dev/zero of=/dev/ram0 bs=1k count=4096

dd if=/dev/zero of=/dev/ram0 bs=1k count=4096

/dev/ram0: No space left on device

4097+0 records in

4096+0 records out

# mke2fs -s0 -vm0 /dev/ram0 4096

mke2fs -s0 -vm0 /dev/ram0 4096

mke2fs 1.25 (20-Sep-2001)

/dev/ram0 is mounted; will not make a filesystem

help me !!