Default can't install TWRP

Trying to install TWRP on my phone... Android Terminal Emulator says: "No space left on the device" and ADB shell says something like Permission denied, however they both have SuperUser permission. What's wrong?
I type:
su
dd if=/sdcard/recovery.img of=/dev/block/mmcblk0p7
and it responds:
/dev/bock/mmcblk0p7: write error: No space left on device
5121+0 records in
5120+0 records out
2621440 bytes transferred in x seconds (xxxxxx bytes/s)