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18.6. Creating devices with mknod and /dev/MAKEDEV 18.6 18. U NIX devices Creating devices with mknod and /dev/MAKEDEV Although all devices are listed in the /dev directory, you can create a device anywhere in the file system using the mknod command: ¨ ¥ mknod [-m <mode>] <file-name> [b|c] <major-number> <minor-number> § ¦ The letters b and c are for creating a block or character device respectively. ¨ To demonstrate, try ¥ mknod -m 0600 ˜/my-floppy b 2 0 ls -al /dev/fd0 ˜/my-floppy ¦ § my-floppy can be used just like /dev/fd0 Note carefully the mode (i.e. the permissions) of /dev/fd0. /dev/fd0 should be readable and writable only to root and to users belonging to the floppy group, since we obviously don’t want an arbitrary user to be able to login (remotely) and write over a floppy disk. In fact, this is the reason for having devices represented as files in the first place. U NIXfiles naturally support group access control, and therefore so also do devices. To create devices that are missing from your /dev directory (some esoteric devices will not be present by default). Simply look up the device’s major and minor number in /usr/src/linux/Documentation/devices.txt and use the mknod command. This is however somewhat tedious, and the script /dev/MAKEDEV is usually present for convenience. You must be in the /dev directory before you run this script. ¨ Typically example usage of MAKEDEV is, cd /dev ./MAKEDEV -v fd0 ./MAKEDEV -v fd1 ¥ ¦ § to create a complete set of floppy disk devices. The man page for MAKEDEV contains more details, and explains the following: Note that programs giving the error “ENOENT: No such file or directory” normally means that the device file is missing, whereas “ENODEV: No such device” normally means the kernel does not have the driver configured or loaded. 144
