You probably mean:
[user] mknod /tmp/dev.0
mknod is a command to make a special file.
On unix "special files" are files that represent (usually) hardware devices. (=definition)
Special files are indicated when issueing the following command:
[nejoom@fire dev]$ cd /dev
[nejoom@fire dev]$ ls -la fd0 zero
brw-rw---- 1 nejoom floppy 2, 0 Aug 30 2001 fd0
crw-rw-rw- 1 root root 1, 5 Aug 30 2001 zero
+------ special file character
b = block (eg floppy)
c = character (eg terminial line)
Writing to a special file sends data directly to the hardware"
]$ cat mytext.txt > /dev/fd0
... reading the special file gets data directly from hardware
In practice most of these special files are located in your /dev directory (devices), and have been made for you at installation.
If your /dev doesn't contain the device you need (if your into attaching esoteric devices), then you might need to use the mknod command.
Take a look at the following if your into this type of stuff: