Why can't dd write to /dev/ram0 on Core Linux?

I created an ext2 file-system on /dev/ram0 ramdisk, and mounted it at /mnt/ram. mkdir /mnt/ram mkext2fs /dev/ram0 sudo mount /dev/ram0 /mnt/ram -o rw Reading from ramdisk with dd works. dd if=/dev/ram0 bs=1 count=1 When I want to write the contents of the file my_file to ramdisk, it fails. dd if=./my_file of=/dev/ram0 bs=1 count=1 0+0 records in 0+0 records out 0 bytes (0B) copied, 0.000913 seconds, 0B/s However, just reading the file dumps its content on stdin. dd if=./my_file bs=1 count=1 The permission on /dev/ram0 shows rw permisssion for root. ls -l /dev/ram0 brw-rw---- 1 root staff 1, 0 Jul 5 02:56 /dev/ram0 What does prevent dd from writing to /dev/ram0?