mknod Post: 23660

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Top Forums UNIX for Dummies Questions & Answers mknod Post 23660 by killerserv on Wednesday 26th of June 2002 08:28:18 PM

06-26-2002

Registered User

In order to use mknod you need to know the major and minor node numbers for the device you wish to create. The devices.txt file in the kernel source documentation is the canonical source of this information.

To take an example, suppose that version of the MAKEDEV script does not know how to create the /dev/ttyS0 device file. Then you need to use mknod to create it. From looking at the devices.txt file that it should be a character device with major number 4 and minor number 64. So you now know all you need to create the file.

Exp:

Code:

	# mknod /dev/ttyS0 c 4 64
	# chown root.dialout /dev/ttyS0
	# chmod 0644 /dev/ttyS0
	# ls -l /dev/ttyS0
crw-rw----   1 root dialout    4,   64 Oct 23 18:23 /dev/ttyS0

As you can see, many more steps are required to create the file. In this example you can see the process required however

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mknod

MKNOD(8)						    BSD System Manager's Manual 						  MKNOD(8)

NAME

     mknod -- make device special file

SYNOPSIS

     mknod [-F format] name [c | b] major minor
     mknod [-F format] name [c | b] major unit subunit
     mknod name [c | b] number
     mknod name w

DESCRIPTION

     The mknod command creates device special files.

     To make nodes manually, the required arguments are:

     name    Device name, for example ``sd'' for a SCSI disk on an HP300 or a ``pty'' for pseudo-devices.

     b | c | w
	     Type of device. If the device is a block type device such as a tape or disk drive which needs both cooked and raw special files, the
	     type is b.  Whiteout nodes are type w.  All other devices are character type devices, such as terminal and pseudo devices, and are
	     type c.

     major   The major device number is an integer number which tells the kernel which device driver entry point to use.

     minor   The minor device number tells the kernel which one of several similar devices the node corresponds to; for example, it may be a spe-
	     cific serial port or pty.

     unit and subunit
	     The unit and subunit numbers select a subset of a device; for example, the unit may specify a particular SCSI disk, and the subunit a
	     partition on that disk.  (Currently this form of specification is only supported by the bsdos format, for compatibility with the
	     BSD/OS mknod(8).)

     Device numbers for different operating systems may be packed in a different format.  To create device nodes that may be used by such an oper-
     ating system (e.g. in an exported file system used for netbooting), the -F option is used.  The following formats are recognized: native,
     386bsd, 4bsd, bsdos, freebsd, hpux, isc, linux, netbsd, osf1, sco, solaris, sunos, svr3, svr4 and ultrix.

     Alternatively, a single opaque device number may be specified.

SEE ALSO

     mkfifo(1), mkfifo(2), mknod(2)

HISTORY

     A mknod command appeared in Version 6 AT&T UNIX.  The -F option appeared in NetBSD 1.4.

NetBSD 1.4							September 11, 1998							NetBSD 1.4