LINUX ALLOCATED DEVICES
	     Maintained by H. Peter Anvin <hpa@zytor.com>

		      Last revised: May 20, 1997

This list is the successor to Rick Miller's Linux Device List, which
he stopped maintaining when he got busy with other things in 1993.  It
is a registry of allocated major device numbers, as well as the
recommended /dev directory nodes for these devices.

The latest version of this list is included with the Linux kernel
sources in LaTeX and ASCII form.  In case of discrepancy, the LaTeX
version is authoritative.

This document is included by reference into the Linux Filesystem
Standard (FSSTND).  The FSSTND is available via FTP from
tsx-11.mit.edu in the directory /pub/linux/docs/linux-standards/fsstnd.

To have a major number allocated, or a minor number in situations
where that applies (e.g. busmice), please contact me with the
appropriate device information.  I *very* much appreciate if you send
me a device description in the same format as the ones already in this
file.  Also, if you have additional information regarding any of the
devices listed below, or if I have made a mistake, I would greatly
appreciate a note.

NOTE: When sending me mail, *please* include the word "device" in the
subject so your mail won't accidentally get buried!

Allocations marked (68k/Amiga) apply to Linux/68k on the Amiga
platform only.  Allocations marked (68k/Atari) apply to Linux/68k on
the Atari platform only.

This document is in the public domain.  The author requests, however,
that semantically altered versions are not distributed without
permission of the author, assuming the author can be contacted without
an unreasonable effort.

In particular, please don't sent patches for this list to Linus, at
least not without contacting me first.

I do not have any information about these devices beyond what appears
on this list.  Any such information requests will be deleted without
reply.

  0 		Unnamed devices (e.g. non-device mounts)
		  0 = reserved as null device number

  1 char	Memory devices
    		  1 = /dev/mem		Physical memory access
		  2 = /dev/kmem		Kernel virtual memory access
		  3 = /dev/null		Null device
		  4 = /dev/port		I/O port access
		  5 = /dev/zero		Null byte source
		  6 = /dev/core		OBSOLETE - replaced by /proc/kcore
		  7 = /dev/full		Returns ENOSPC on write
		  8 = /dev/random	Nondeterministic random number gen.
		  9 = /dev/urandom	Faster, less secure random number gen.
    block	RAM disk
		  0 = /dev/ram0		First RAM disk
		    ...
		  7 = /dev/ram7		Eighth RAM disk
		250 = /dev/initrd	Initial RAM disk

		Older kernels had /dev/ramdisk (1, 1) here.
		/dev/initrd refers to a RAM disk which was preloaded
		by the boot loader.
		    
  2 char	Pseudo-TTY masters
		  0 = /dev/ptyp0	First PTY master
		  1 = /dev/ptyp1	Second PTY master
		    ...
		255 = /dev/ptyef	256th PTY master

		Pseudo-tty's are named as follows:
		* Masters are "pty", slaves are "tty";
		* the fourth letter is one of pqrstuvwxyzabcde indicating
		  the 1st through 16th series of 16 pseudo-ttys each, and
		* the fifth letter is one of 0123456789abcdef indicating
		  the position within the series.
  
    block	Floppy disks
		  0 = /dev/fd0		First floppy disk autodetect
		  1 = /dev/fd1		Second floppy disk autodetect
		  2 = /dev/fd2		Third floppy disk autodetect
		  3 = /dev/fd3		Fourth floppy disk autodetect

		To specify format, add to the autodetect device number:
		  0 = /dev/fd?		Autodetect format
		  4 = /dev/fd?d360	5.25"  360K in a 360K  drive(1)
		 20 = /dev/fd?h360	5.25"  360K in a 1200K drive(1)
		 48 = /dev/fd?h410	5.25"  410K in a 1200K drive
		 64 = /dev/fd?h420	5.25"  420K in a 1200K drive
		 24 = /dev/fd?h720	5.25"  720K in a 1200K drive
		 80 = /dev/fd?h880	5.25"  880K in a 1200K drive(1)
		  8 = /dev/fd?h1200	5.25" 1200K in a 1200K drive(1)
		 40 = /dev/fd?h1440	5.25" 1440K in a 1200K drive(1)
		 56 = /dev/fd?h1476	5.25" 1476K in a 1200K drive
	  	 72 = /dev/fd?h1494	5.25" 1494K in a 1200K drive
		 92 = /dev/fd?h1600	5.25" 1600K in a 1200K drive(1)

		 12 = /dev/fd?u360	3.5"   360K Double Density
		120 = /dev/fd?u800	3.5"   800K Double Density(1)
		 52 = /dev/fd?u820	3.5"   820K Double Density(2)
		 68 = /dev/fd?u830	3.5"   830K Double Density
		 84 = /dev/fd?u1040	3.5"  1040K Double Density(1)
		 88 = /dev/fd?u1120	3.5"  1120K Double Density(1)
		 28 = /dev/fd?u1440	3.5"  1440K High Density(1)
		124 = /dev/fd?u1600	3.5"  1600K High Density(1)
		 44 = /dev/fd?u1680	3.5"  1680K High Density(3)
		 60 = /dev/fd?u1722	3.5"  1722K High Density
		 76 = /dev/fd?u1743	3.5"  1743K High Density
		 96 = /dev/fd?u1760	3.5"  1760K High Density
		116 = /dev/fd?u1840	3.5"  1840K High Density(3)
		100 = /dev/fd?u1920	3.5"  1920K High Density(1)
		 32 = /dev/fd?u2880	3.5"  2880K Extra Density(1)
		104 = /dev/fd?u3200	3.5"  3200K Extra Density
		108 = /dev/fd?u3520	3.5"  3520K Extra Density
		112 = /dev/fd?u3840	3.5"  3840K Extra Density(1)

		 36 = /dev/fd?CompaQ	Compaq 2880K drive; obsolete?

		(1) Autodetectable format
		(2) Autodetectable format in a Double Density (720K) drive only
		(3) Autodetectable format in a High Density (1440K) drive only

		NOTE: The letter in the device name (d, q, h or u)
		signifies the type of drive: 5.25" Double Density (d),
		5.25" Quad Density (q), 5.25" High Density (h) or 3.5"
		(any model, u).  The use of the capital letters D, H
		and E for the 3.5" models have been deprecated, since
		the drive type is insignificant for these devices.

  3 char	Pseudo-TTY slaves
		  0 = /dev/ttyp0	First PTY slave
		  1 = /dev/ttyp1	Second PTY slave
		    ...
		256 = /dev/ttyef	256th PTY slave

    block	First MFM, RLL and IDE hard disk/CD-ROM interface
    		  0 = /dev/hda		Master: whole disk (or CD-ROM)
		 64 = /dev/hdb		Slave: whole disk (or CD-ROM)
		
		For partitions, add to the whole disk device number:
		  0 = /dev/hd?		Whole disk
		  1 = /dev/hd?1		First partition
		  2 = /dev/hd?2		Second partition
		    ...
		 63 = /dev/hd?63	63rd partition

		For Linux/i386, partitions 1-4 are the primary
		partitions, and 5 and above are logical partitions.
		Other versions of Linux use partitioning schemes
		appropriate to their respective architectures.
		
  4 char	TTY devices
    		  0 = /dev/console	Console device

		  1 = /dev/tty1		First virtual console
		      ...
		 63 = /dev/tty63	63rd virtual console
		 64 = /dev/ttyS0	First serial port
		      ...
		127 = /dev/ttyS63	64th serial port
		128 = /dev/ptyp0	First old pseudo-tty master
		      ...
		191 = /dev/ptysf	64th old pseudo-tty master
		192 = /dev/ttyp0	First old pseudo-tty slave
		      ...
		255 = /dev/ttysf	64th old pseudo-tty slave

		For compatibility with previous versions of Linux, the
		first 64 PTYs are replicated under this device number.
		This use is deprecated with the release of Linux 2.0
		and may be removed in a future version of Linux.  To
		ensure proper operation, do not mix old and new PTY
		devices.

  5 char	Alternate TTY devices
    		  0 = /dev/tty		Current TTY device
		 64 = /dev/cua0		Callout device corresponding to ttyS0
		      ...
		127 = /dev/cua63	Callout device corresponding to ttyS63

  6 char	Parallel printer devices
    		  0 = /dev/lp0		First parallel printer (0x3bc)
		  1 = /dev/lp1		Second parallel printer (0x378)
		  2 = /dev/lp2		Third parallel printer (0x278)

		Not all computers have the 0x3bc parallel port; hence
		the "first" printer may be either /dev/lp0 or
		/dev/lp1.

  7 char	Virtual console capture devices
    		  0 = /dev/vcs		Current vc text contents
		  1 = /dev/vcs1		tty1 text contents
		      ...
		 63 = /dev/vcs63	tty63 text contents
		128 = /dev/vcsa		Current vc text/attribute contents
		129 = /dev/vcsa1	tty1 text/attribute contents
		      ...
		191 = /dev/vcsa63	tty63 text/attribute contents
	
		NOTE: These devices permit both read and write access.

    block	Loopback devices
		  0 = /dev/loop0	First loopback device
		  1 = /dev/loop1	Second loopback device
		      ...

		The loopback devices are used to mount filesystems not
		associated with block devices.  The binding to the
		loopback devices is handled by mount(8) or losetup(8).

  8 block	SCSI disk devices
    		  0 = /dev/sda		First SCSI disk whole disk
		 16 = /dev/sdb		Second SCSI disk whole disk
		 32 = /dev/sdc		Third SCSI disk whole disk
  		      ...
		240 = /dev/sdp		Sixteenth SCSI disk whole disk

		Partitions are handled in the same way as for IDE
		disks (see major number 3) except that the limit on
		partitions is 15.

  9 char	SCSI tape devices
    		  0 = /dev/st0		First SCSI tape, mode 0
		  1 = /dev/st1		Second SCSI tape, mode 0
		      ...
    		 32 = /dev/st0l		First SCSI tape, mode 1
		 33 = /dev/st1l		Second SCSI tape, mode 1
		      ...
    		 64 = /dev/st0m		First SCSI tape, mode 2
		 65 = /dev/st1m		Second SCSI tape, mode 2
		      ...
    		 96 = /dev/st0a		First SCSI tape, mode 3
		 97 = /dev/st1a		Second SCSI tape, mode 3
		      ...
		128 = /dev/nst0		First SCSI tape, mode 0, no rewind
		129 = /dev/nst1		Second SCSI tape, mode 0, no rewind
		      ...
		160 = /dev/nst0l	First SCSI tape, mode 1, no rewind
		161 = /dev/nst1l	Second SCSI tape, mode 1, no rewind
		      ...
		192 = /dev/nst0m	First SCSI tape, mode 2, no rewind
		193 = /dev/nst1m	Second SCSI tape, mode 2, no rewind
		      ...
		224 = /dev/nst0a	First SCSI tape, mode 3, no rewind
		225 = /dev/nst1a	Second SCSI tape, mode 3, no rewind
		      ...

		"No rewind" refers to the omission of the default
		automatic rewind on device close.  The MTREW or MTOFFL
		ioctl()'s can be used to rewind the tape regardless of
		the device used to access it.

    block	Metadisk (RAID) devices
		  0 = /dev/md0		First metadisk group
		  1 = /dev/md1		Second metadisk group
		      ...

		The metadisk driver is used to span a
		filesystem across multiple physical disks.

 10 char	Non-serial mice, misc features
		  0 = /dev/logibm	Logitech bus mouse
		  1 = /dev/psaux	PS/2-style mouse port
		  2 = /dev/inportbm	Microsoft Inport bus mouse
		  3 = /dev/atibm	ATI XL bus mouse
		  4 = /dev/jbm		J-mouse
		  4 = /dev/amigamouse	Amiga mouse (68k/Amiga)
		  5 = /dev/atarimouse	Atari mouse
		  6 = /dev/sunmouse	Sun mouse
		  7 = /dev/amigamouse1	Second Amiga mouse
		  8 = /dev/smouse	Simple serial mouse driver
		  9 = /dev/pc110pad	IBM PC-110 digitizer pad
		128 = /dev/beep		Fancy beep device
		129 = /dev/modreq	Kernel module load request
		130 = /dev/watchdog	Watchdog timer port
		131 = /dev/temperature	Machine internal temperature
		132 = /dev/hwtrap	Hardware fault trap
		133 = /dev/exttrp	External device trap
		134 = /dev/apm_bios	Advanced Power Management BIOS
		135 = /dev/rtc		Real Time Clock
		136 = /dev/qcam0	QuickCam on lp0
		137 = /dev/qcam1	QuickCam on lp1
		138 = /dev/qcam2	QuickCam on lp2
		139 = /dev/openprom	SPARC OpenBoot PROM
		140 = /dev/relay8	Berkshire Products Octal relay card
		141 = /dev/relay16	Berkshire Products ISO-16 relay card
		142 = /dev/msr		x86 model-specific registers
		143 = /dev/pciconf	PCI configuration space
		144 = /dev/nvram	Non-volatile configuration RAM

 11 char	Raw keyboard device
		  0 = /dev/kbd		Raw keyboard device

		The raw keyboard device is used on Linux/SPARC only.

    block	SCSI CD-ROM devices
    		  0 = /dev/sr0		First SCSI CD-ROM
		  1 = /dev/sr1		Second SCSI CD-ROM
		      ...

		The prefix /dev/scd instead of /dev/sr has been used
		as well, and might make more sense.

 12 char	QIC-02 tape
		  2 = /dev/ntpqic11	QIC-11, no rewind-on-close
		  3 = /dev/tpqic11	QIC-11, rewind-on-close
		  4 = /dev/ntpqic24	QIC-24, no rewind-on-close
		  5 = /dev/tpqic24	QIC-24, rewind-on-close
		  6 = /dev/ntpqic120	QIC-120, no rewind-on-close
		  7 = /dev/tpqic120	QIC-120, rewind-on-close
		  8 = /dev/ntpqic150	QIC-150, no rewind-on-close
		  9 = /dev/tpqic150	QIC-150, rewind-on-close

		The device names specified are proposed -- if there
		are "standard" names for these devices, please let me know.

    block	MSCDEX CD-ROM callback support
		  0 = /dev/dos_cd0	First MSCDEX CD-ROM
		  1 = /dev/dos_cd1	Second MSCDEX CD-ROM
		      ...

 13 char	PC speaker
		  0 = /dev/pcmixer	Emulates /dev/mixer
		  1 = /dev/pcsp		Emulates /dev/dsp (8-bit)
		  4 = /dev/pcaudio	Emulates /dev/audio
		  5 = /dev/pcsp16	Emulates /dev/dsp (16-bit)
    block	8-bit MFM/RLL/IDE controller
		  0 = /dev/xda		First XT disk whole disk
		 64 = /dev/xdb		Second XT disk whole disk

		Partitions are handled in the same way as IDE disks
		(see major number 3).

 14 char	Sound card
		  0 = /dev/mixer	Mixer control
		  1 = /dev/sequencer	Audio sequencer
		  2 = /dev/midi00	First MIDI port
		  3 = /dev/dsp		Digital audio
		  4 = /dev/audio	Sun-compatible digital audio
		  6 = /dev/sndstat	Sound card status information
		  8 = /dev/sequencer2	Sequencer -- alternate device
		 16 = /dev/mixer1	Second soundcard mixer control
		 17 = /dev/patmgr0	Sequencer patch manager
		 18 = /dev/midi01	Second MIDI port
		 19 = /dev/dsp1		Second soundcard digital audio
		 20 = /dev/audio1	Second soundcard Sun digital audio
		 33 = /dev/patmgr1	Sequencer patch manager
		 34 = /dev/midi02	Third MIDI port
		 50 = /dev/midi03	Fourth MIDI port
    block	BIOS harddrive callback support
		  0 = /dev/dos_hda	First BIOS harddrive whole disk
		 64 = /dev/dos_hdb	Second BIOS harddrive whole disk
		128 = /dev/dos_hdc	Third BIOS harddrive whole disk
		192 = /dev/dos_hdd	Fourth BIOS harddrive whole disk

		Partitions are handled in the same way as IDE disks
		(see major number 3).

 15 char	Joystick
		  0 = /dev/js0		First analog joystick
		  1 = /dev/js1		Second analog joystick
		    ...
		128 = /dev/djs0		First digital joystick
		129 = /dev/djs1		Second digital joystick
		    ...
    block	Sony CDU-31A/CDU-33A CD-ROM
		  0 = /dev/sonycd	Sony CDU-31a CD-ROM

 16 char	Non-SCSI scanners
		  0 = /dev/gs4500	Genius 4500 handheld scanner
    block	GoldStar CD-ROM
		  0 = /dev/gscd		GoldStar CD-ROM

 17 char	Chase serial card
		  0 = /dev/ttyH0	First Chase port
		  1 = /dev/ttyH1	Second Chase port
		      ...
    block	Optics Storage CD-ROM
		  0 = /dev/optcd	Optics Storage CD-ROM

 18 char	Chase serial card - alternate devices
		  0 = /dev/cuh0		Callout device corresponding to ttyH0
		  1 = /dev/cuh1		Callout device corresponding to ttyH1
		      ...
    block	Sanyo CD-ROM
		  0 = /dev/sjcd		Sanyo CD-ROM

 19 char	Cyclades serial card
		  0 = /dev/ttyC0	First Cyclades port
		      ...
		 31 = /dev/ttyC31	32nd Cyclades port
    block	"Double" compressed disk
		  0 = /dev/double0	First compressed disk
		      ...
		  7 = /dev/double7	Eighth compressed disk
		128 = /dev/cdouble0	Mirror of first compressed disk
		      ...
		135 = /dev/cdouble7	Mirror of eighth compressed disk

		See the Double documentation for the meaning of the
		mirror devices.

 20 char	Cyclades serial card - alternate devices
		  0 = /dev/cub0		Callout device corresponding to ttyC0
		      ...
		 31 = /dev/cub31	Callout device corresponding to ttyC31
    block	Hitachi CD-ROM (under development)
		  0 = /dev/hitcd	Hitachi CD-ROM

 21 char	Generic SCSI access
		  0 = /dev/sg0		First generic SCSI device
		  1 = /dev/sg1		Second generic SCSI device
		      ...

		Most distributions name these /dev/sga, /dev/sgb...;
		this sets an unnecessary limit of 26 SCSI devices in
		the system and is counter to standard Linux
		device-naming practice.

 22 char	Digiboard serial card
		  0 = /dev/ttyD0	First Digiboard port
		  1 = /dev/ttyD1	Second Digiboard port
		      ...
    block	Second IDE hard disk/CD-ROM interface
    		  0 = /dev/hdc		Master: whole disk (or CD-ROM)
		 64 = /dev/hdd		Slave: whole disk (or CD-ROM)
		
		Partitions are handled the same way as for the first
		interface (see major number 3).

 23 char	Digiboard serial card - alternate devices
		  0 = /dev/cud0		Callout device corresponding to ttyD0
		  1 = /dev/cud1		Callout device corresponding to ttyD1
		      ...
    block	Mitsumi proprietary CD-ROM
		  0 = /dev/mcd		Mitsumi CD-ROM

 24 char	Stallion serial card
		  0 = /dev/ttyE0	Stallion port 0 card 0
		  1 = /dev/ttyE1	Stallion port 1 card 0
		      ...
		 64 = /dev/ttyE64	Stallion port 0 card 1
		 65 = /dev/ttyE65	Stallion port 1 card 1
		      ...
		128 = /dev/ttyE128	Stallion port 0 card 2
		129 = /dev/ttyE129	Stallion port 1 card 2
		      ...
		192 = /dev/ttyE192	Stallion port 0 card 3
		193 = /dev/ttyE193	Stallion port 1 card 3
		      ...
    block	Sony CDU-535 CD-ROM
		  0 = /dev/cdu535	Sony CDU-535 CD-ROM

 25 char	Stallion serial card - alternate devices
		  0 = /dev/cue0		Callout device corresponding to ttyE0
		  1 = /dev/cue1		Callout device corresponding to ttyE1
		      ...
		 64 = /dev/cue64	Callout device corresponding to ttyE64
		 65 = /dev/cue65	Callout device corresponding to ttyE65
		      ...
		128 = /dev/cue128	Callout device corresponding to ttyE128
		129 = /dev/cue129	Callout device corresponding to ttyE129
		      ...
		192 = /dev/cue192	Callout device corresponding to ttyE192
		193 = /dev/cue193	Callout device corresponding to ttyE193
		      ...
    block	First Matsushita (Panasonic/SoundBlaster) CD-ROM
		  0 = /dev/sbpcd0	Panasonic CD-ROM controller 0 unit 0
		  1 = /dev/sbpcd1	Panasonic CD-ROM controller 0 unit 1
		  2 = /dev/sbpcd2	Panasonic CD-ROM controller 0 unit 2
		  3 = /dev/sbpcd3	Panasonic CD-ROM controller 0 unit 3

 26 char	Quanta WinVision frame grabber
		  0 = /dev/wvisfgrab	Quanta WinVision frame grabber
    block	Second Matsushita (Panasonic/SoundBlaster) CD-ROM
		  0 = /dev/sbpcd4	Panasonic CD-ROM controller 1 unit 0
		  1 = /dev/sbpcd5	Panasonic CD-ROM controller 1 unit 1
		  2 = /dev/sbpcd6	Panasonic CD-ROM controller 1 unit 2
		  3 = /dev/sbpcd7	Panasonic CD-ROM controller 1 unit 3

 27 char	QIC-117 tape
		  0 = /dev/rft0		Unit 0, rewind-on-close
		  1 = /dev/rft1		Unit 1, rewind-on-close
		  2 = /dev/rft2		Unit 2, rewind-on-close
		  3 = /dev/rft3		Unit 3, rewind-on-close
		  4 = /dev/nrft0	Unit 0, no rewind-on-close
		  5 = /dev/nrft1	Unit 1, no rewind-on-close
		  6 = /dev/nrft2	Unit 2, no rewind-on-close
		  7 = /dev/nrft3	Unit 3, no rewind-on-close
    block	Third Matsushita (Panasonic/SoundBlaster) CD-ROM
		  0 = /dev/sbpcd8	Panasonic CD-ROM controller 2 unit 0
		  1 = /dev/sbpcd9	Panasonic CD-ROM controller 2 unit 1
		  2 = /dev/sbpcd10	Panasonic CD-ROM controller 2 unit 2
		  3 = /dev/sbpcd11	Panasonic CD-ROM controller 2 unit 3

 28 char	Stallion serial card - card programming
		  0 = /dev/staliomem0	First Stallion card I/O memory
		  1 = /dev/staliomem1	Second Stallion card I/O memory
		  2 = /dev/staliomem2	Third Stallion card I/O memory
		  3 = /dev/staliomem3	Fourth Stallion card I/O memory
    char	Atari SLM ACSI laser printer (68k/Atari)
		  0 = /dev/slm0		First SLM laser printer
		  1 = /dev/slm1		Second SLM laser printer
		      ...
    block	Fourth Matsushita (Panasonic/SoundBlaster) CD-ROM
		  0 = /dev/sbpcd12	Panasonic CD-ROM controller 3 unit 0
		  1 = /dev/sbpcd13	Panasonic CD-ROM controller 3 unit 1
		  2 = /dev/sbpcd14	Panasonic CD-ROM controller 3 unit 2
		  3 = /dev/sbpcd15	Panasonic CD-ROM controller 3 unit 3
    block	ACSI disk (68k/Atari)
		  0 = /dev/ada		First ACSI disk whole disk
		 16 = /dev/adb		Second ACSI disk whole disk
		 32 = /dev/adc		Third ACSI disk whole disk
		      ...
		240 = /dev/adp		16th ACSI disk whole disk

		Partitions are handled in the same way as for IDE
		disks (see major number 3) except that the limit on
		partitions is 15, like SCSI.

 29 char	Universal frame buffer
		  0 = /dev/fb0		First frame buffer
		  1 = /dev/fb0autodetect
		 24 = /dev/fb0user0
	              ...
		 31 = /dev/fb0user7
		 32 = /dev/fb1		Second frame buffer
		 33 = /dev/fb1autodetect
		 56 = /dev/fb1user0
		      ...
		 63 = /dev/fb1user7

		The universal frame buffer device is currently only
		supported on Linux/68k and Linux/SPARC.  The plain
		device accesses the frame buffer at current resolution
		(Linux/68k calls this device "current",
		e.g. /dev/fb0current); the "autodetect" one at bootup
		(default) resolution.  Minor numbers 2-23 within each
		frame buffer assignment are used for specific
		device-dependent resolutions.  There appears to be no
		standard naming for these devices.  Finally, 2-31
		within each device are reserved for user-selected
		modes, usually entered at boot time.  Currently only
		Linux/68k uses the mode-specific devices.

    block	Aztech/Orchid/Okano/Wearnes CD-ROM
		  0 = /dev/aztcd	Aztech CD-ROM

 30 char	iBCS-2 compatibility devices
		  0 = /dev/socksys	Socket access
		  1 = /dev/spx		SVR3 local X interface
		  2 = /dev/inet/arp	Network access
		  2 = /dev/inet/icmp	Network access
		  2 = /dev/inet/ip	Network access
		  2 = /dev/inet/udp	Network access
		  2 = /dev/inet/tcp	Network access

		iBCS-2 requires /dev/nfsd to be a link to
		/dev/socksys, and /dev/X0R to be a link to /dev/null.

    block	Philips LMS CM-205 CD-ROM
		  0 = /dev/cm205cd	Philips LMS CM-205 CD-ROM

		/dev/lmscd is an older name for this device.  This
		driver does not work with the CM-205MS CD-ROM.

 31 char	MPU-401 MIDI
		  0 = /dev/mpu401data	MPU-401 data port
		  1 = /dev/mpu401stat	MPU-401 status port
    block	ROM/flash memory card
		  0 = /dev/rom0		First ROM card (rw)
		      ...
		  7 = /dev/rom7		Eighth ROM card (rw)
		  8 = /dev/rrom0	First ROM card (ro)
		      ...
		 15 = /dev/rrom7	Eighth ROM card (ro)
		 16 = /dev/flash0	First flash memory card (rw)
		      ...
		 23 = /dev/flash7	Eighth flash memory card (rw)
		 24 = /dev/rflash0	First flash memory card (ro)
		      ...
		 31 = /dev/rflash7	Eighth flash memory card (ro)

		The read-write (rw) devices support back-caching
		written data in RAM, as well as writing to flash RAM
		devices.  The read-only devices (ro) support reading
		only.

 32 char	Specialix serial card
		  0 = /dev/ttyX0	First Specialix port
		  1 = /dev/ttyX1	Second Specialix port
		      ...
    block	Philips LMS CM-206 CD-ROM
		  0 = /dev/cm206cd	Philips LMS CM-206 CD-ROM

 33 char	Specialix serial card - alternate devices
		  0 = /dev/cux0		Callout device corresponding to ttyX0
		  1 = /dev/cux1		Callout device corresponding to ttyX1
		      ...
    block	Third IDE hard disk/CD-ROM interface
    		  0 = /dev/hde		Master: whole disk (or CD-ROM)
		 64 = /dev/hdf		Slave: whole disk (or CD-ROM)

		Partitions are handled the same way as for the first
		interface (see major number 3).

 34 char	Z8530 HDLC driver
		  0 = /dev/scc0		First Z8530, first port
		  1 = /dev/scc1		First Z8530, second port
		  2 = /dev/scc2		Second Z8530, first port
		  3 = /dev/scc3		Second Z8530, second port
		      ...

		In a previous version these devices were named
		/dev/sc1 for /dev/scc0, /dev/sc2 for /dev/scc1, and so
		on.

    block	Fourth IDE hard disk/CD-ROM interface
    		  0 = /dev/hdg		Master: whole disk (or CD-ROM)
		 64 = /dev/hdh		Slave: whole disk (or CD-ROM)
		
		Partitions are handled the same way as for the first
		interface (see major number 3).

 35 char	tclmidi MIDI driver
		  0 = /dev/midi0	First MIDI port, kernel timed
		  1 = /dev/midi1	Second MIDI port, kernel timed
		  2 = /dev/midi2	Third MIDI port, kernel timed
		  3 = /dev/midi3	Fourth MIDI port, kernel timed
	         64 = /dev/rmidi0	First MIDI port, untimed
	         65 = /dev/rmidi1	Second MIDI port, untimed
	         66 = /dev/rmidi2	Third MIDI port, untimed
	         67 = /dev/rmidi3	Fourth MIDI port, untimed
		128 = /dev/smpte0	First MIDI port, SMPTE timed
		129 = /dev/smpte1	Second MIDI port, SMPTE timed
		130 = /dev/smpte2	Third MIDI port, SMPTE timed
		131 = /dev/smpte3	Fourth MIDI port, SMPTE timed

 36 char	Netlink support
		  0 = /dev/route	Routing, device updates, kernel to user
		  1 = /dev/skip		enSKIP security cache control
    block	MCA ESDI hard disk
		  0 = /dev/eda		First ESDI disk whole disk
		 64 = /dev/edb		Second ESDI disk whole disk
		      ...

		Partitions are handled in the same way as IDE disks
		(see major number 3).

 37 char	IDE tape
		  0 = /dev/ht0		First IDE tape
		128 = /dev/nht0		First IDE tape, no rewind-on-close

		Currently, only one IDE tape drive is supported.

    block	Zorro II ramdisk
		  0 = /dev/z2ram	Zorro II ramdisk

 38 char	Myricom PCI Myrinet board
		  0 = /dev/mlanai0	First Myrinet board
		  1 = /dev/mlanai1	Second Myrinet board
		      ...

		This device is used for status query, board control
		and "user level packet I/O."  This board is also
		accessible as a standard networking "eth" device.

    block	Reserved for Linux/AP+

 39 char	ML-16P experimental I/O board
		  0 = /dev/ml16pa-a0	First card, first analog channel
		  1 = /dev/ml16pa-a1	First card, second analog channel
		      ...
		 15 = /dev/ml16pa-a15	First card, 16th analog channel
		 16 = /dev/ml16pa-d	First card, digital lines
		 17 = /dev/ml16pa-c0	First card, first counter/timer
		 18 = /dev/ml16pa-c1	First card, second counter/timer
		 19 = /dev/ml16pa-c2	First card, third counter/timer
		 32 = /dev/ml16pb-a0	Second card, first analog channel
		 33 = /dev/ml16pb-a1	Second card, second analog channel
		      ...
		 47 = /dev/ml16pb-a15	Second card, 16th analog channel
		 48 = /dev/ml16pb-d	Second card, digital lines
		 49 = /dev/ml16pb-c0	Second card, first counter/timer
		 50 = /dev/ml16pb-c1	Second card, second counter/timer
		 51 = /dev/ml16pb-c2	Second card, third counter/timer
		      ...
    block	Reserved for Linux/AP+

 40 char	Matrox Meteor frame grabber
		  0 = /dev/mmetfgrab	Matrox Meteor frame grabber
    block	Syquest EZ135 parallel port removable drive
		  0 = /dev/eza		Parallel EZ135 drive, whole disk

		Partitions are handled in the same way as IDE disks
		(see major number 3).

 41 char	Yet Another Micro Monitor
		  0 = /dev/yamm		Yet Another Micro Monitor
    block	MicroSolutions BackPack parallel port CD-ROM
		  0 = /dev/bpcd		BackPack CD-ROM

 42		Demo/sample use

		This number is intended for use in sample code, as
		well as a general "example" device number.  It
		should never be used for a device driver that is being
		distributed; either obtain an official number or use
		the local/experimental range.  The sudden addition or
		removal of a driver with this number should not cause
		ill effects to the system (bugs excepted.)

 43 char	isdn4linux virtual modem
		  0 = /dev/ttyI0	First virtual modem
		      ...
		 63 = /dev/ttyI63	64th virtual modem
    block	Network block devices
		  0 = /dev/nb0		First network block device
		  1 = /dev/nb1		Second network block device
		      ...

		Network Block Device is somehow similar to loopback
		devices: If you read from it, it sends packet accross
		network asking server for data. If you write to it, it
		sends packet telling server to write. It could be used
		to mounting filesystems over the net, swapping over
		the net, implementing block device in userland etc.

 44 char	isdn4linux virtual modem - alternate devices
		  0 = /dev/cui0		Callout device corresponding to ttyI0
		      ...
		 63 = /dev/cui63	Callout device corresponding to ttyI63

 45 char	isdn4linux ISDN BRI driver
		  0 = /dev/isdn0	First virtual B channel raw data
		      ...
		 63 = /dev/isdn63	64th virtual B channel raw data
		 64 = /dev/isdnctrl0	First channel control/debug
		      ...
		127 = /dev/isdnctrl63	64th channel control/debug

		128 = /dev/ippp0	First SyncPPP device
		      ...
		191 = /dev/ippp63	64th SyncPPP device

		255 = /dev/isdninfo	ISDN monitor interface

 46 char	Comtrol Rocketport serial card
		  0 = /dev/ttyR0	First Rocketport port
		  1 = /dev/ttyR1	Second Rocketport port
		      ...

 47 char	Comtrol Rocketport serial card - alternate devices
		  0 = /dev/cur0		Callout device corresponding to ttyR0
		  1 = /dev/cur1		Callout device corresponding to ttyR1
		      ...

 48 char	SDL RISCom serial card
		  0 = /dev/ttyL0	First RISCom port
		  1 = /dev/ttyL1	Second RISCom port
		      ...

 49 char	SDL RISCom serial card - alternate devices
		  0 = /dev/cul0		Callout device corresponding to ttyL0
		  1 = /dev/cul1		Callout device corresponding to ttyL1
		      ...

 50 char	Reserved for GLINT

 51 char	Baycom radio modem
		  0 = /dev/bc0		First Baycom radio modem
		  1 = /dev/bc1		Second Baycom radio modem
		      ...

 52 char	Spellcaster DataComm/BRI ISDN card
		  0 = /dev/dcbri0	First DataComm card
		  1 = /dev/dcbri1	Second DataComm card
		  2 = /dev/dcbri2	Third DataComm card
		  3 = /dev/dcbri3	Fourth DataComm card

 53 char	BDM interface for remote debugging MC683xx microcontrollers
		  0 = /dev/pd_bdm0	PD BDM interface on lp0
          	  1 = /dev/pd_bdm1	PD BDM interface on lp1
          	  2 = /dev/pd_bdm2	PD BDM interface on lp2
		  4 = /dev/icd_bdm0	ICD BDM interface on lp0
		  5 = /dev/icd_bdm1	ICD BDM interface on lp1
		  6 = /dev/icd_bdm2	ICD BDM interface on lp2

		This device is used for the interfacing to the MC683xx
		microcontrollers via Background Debug Mode by use of a
		Parallel Port interface. PD is the Motorola Public
		Domain Interface and ICD is the commercial interface
		by P&E.

 54 char	Electrocardiognosis Holter serial card
		  0 = /dev/holter0	First Holter port
		  1 = /dev/holter1	Second Holter port
		  2 = /dev/holter2	Third Holter port

		A custom serial card used by Electrocardiognosis SRL
		<mseritan@ottonel.pub.ro> to transfer data from Holter
		24-hour heart monitoring equipment.

 55 char	DSP56001 digital signal processor
		  0 = /dev/dsp56k	First DSP56001

 56 char	Apple Desktop Bus
		  0 = /dev/adb		ADB bus control

		Additional devices will be added to this number, all
		starting with /dev/adb.

 57 char	Hayes ESP serial card
		  0 = /dev/ttyP0	First ESP port
		  1 = /dev/ttyP1	Second ESP port
		      ...

 58 char	Hayes ESP serial card - alternate devices
		  0 = /dev/cup0		Callout device corresponding to ttyP0
		  1 = /dev/cup1		Callout device corresponding to ttyP1
		      ...

 59 char	sf firewall package
		  0 = /dev/firewall	Communication with sf kernel module

 60-63		LOCAL/EXPERIMENTAL USE
		Allocated for local/experimental use.  For devices not
		assigned official numbers, these ranges should be
		used, in order to avoid conflicting with future assignments.

 64 char	ENskip kernel encryption package
		  0 = /dev/enskip	Communication with ENskip kernel module

 65 char	Sundance "plink" Transputer boards
		  0 = /dev/plink0	First plink device
		  1 = /dev/plink1	Second plink device
		  2 = /dev/plink2	Third plink device
		  3 = /dev/plink3	Fourth plink device
		 64 = /dev/rplink0	First plink device, raw
		 65 = /dev/rplink1	Second plink device, raw
		 66 = /dev/rplink2	Third plink device, raw
		 67 = /dev/rplink3	Fourth plink device, raw
		128 = /dev/plink0d	First plink device, debug
		129 = /dev/plink1d	Second plink device, debug
		130 = /dev/plink2d	Third plink device, debug
		131 = /dev/plink3d	Fourth plink device, debug
		192 = /dev/rplink0d	First plink device, raw, debug
		193 = /dev/rplink1d	Second plink device, raw, debug
		194 = /dev/rplink2d	Third plink device, raw, debug
		195 = /dev/rplink3d	Fourth plink device, raw, debug

		This is a commercial driver; contact James Howes
		<jth@prosig.demon.co.uk> for information.

 66 char	YARC PowerPC PCI coprocessor card
		  0 = /dev/yppcpci0	First YARC card
		  1 = /dev/yppcpci1	Second YARC card
		      ...

 67 char	Coda network file system
		  0 = /dev/cfs0		Coda cache manager

		See http://www.coda.cs.cmu.edu for information about Coda.

 68 char	CAPI 2.0 interface
		  0 = /dev/capi20	Control device
		  1 = /dev/capi20.00	First CAPI 2.0 application
		  2 = /dev/capi20.01	Second CAPI 2.0 application
		      ...
		 20 = /dev/capi20.19	19th CAPI 2.0 application

		ISDN CAPI 2.0 driver for use with CAPI 2.0
		applications; currently supports the AVM B1 card.

 69 char	MA16 numeric accelerator card
		  0 = /dev/ma16		Board memory access

 70 char	SpellCaster Protocol Services Interface
		  0 = /dev/apscfg	Configuration interface
		  1 = /dev/apsauth	Authentication interface
		  2 = /dev/apslog	Logging interface
		  3 = /dev/apsdbg	Debugging interface
		 64 = /dev/apsisdn	ISDN command interface
		 65 = /dev/apsasync	Async command interface
		128 = /dev/apsmon	Monitor interface

 71 char	Computone IntelliPort II serial card
		  0 = /dev/ttyF0	IntelliPort II board 0, port 0
		  1 = /dev/ttyF1	IntelliPort II board 0, port 1
		      ...
		 63 = /dev/ttyF63	IntelliPort II board 0, port 63
		 64 = /dev/ttyF64	IntelliPort II board 1, port 0
		 65 = /dev/ttyF65	IntelliPort II board 1, port 1
		      ...
		127 = /dev/ttyF127	IntelliPort II board 1, port 63
		128 = /dev/ttyF128	IntelliPort II board 2, port 0
		129 = /dev/ttyF129	IntelliPort II board 2, port 1
		      ...
		191 = /dev/ttyF191	IntelliPort II board 2, port 63
		192 = /dev/ttyF192	IntelliPort II board 3, port 0
		193 = /dev/ttyF193	IntelliPort II board 3, port 1
		      ...
		255 = /dev/ttyF255	IntelliPort II board 3, port 63

 72 char	Computone IntelliPort II serial card - alternate devices
		  0 = /dev/cuf0		Callout device corresponding to ttyF0
		  1 = /dev/cuf1		Callout device corresponding to ttyF1
		      ...
		 63 = /dev/cuf63	Callout device corresponding to ttyF63
		 64 = /dev/cuf64	Callout device corresponding to ttyF64
		 65 = /dev/cuf65	Callout device corresponding to ttyF65
		      ...
		127 = /dev/cuf127	Callout device corresponding to ttyF127
		128 = /dev/cuf128	Callout device corresponding to ttyF128
		129 = /dev/cuf129	Callout device corresponding to ttyF129
		      ...
		191 = /dev/cuf191	Callout device corresponding to ttyF191
		192 = /dev/cuf192	Callout device corresponding to ttyF192
		193 = /dev/cuf193	Callout device corresponding to ttyF193
		      ...
		255 = /dev/cuf255	Callout device corresponding to ttyF255

 73 char	Computone IntelliPort II serial card - control devices
		  0 = /dev/ip2ipl0	Loadware device for board 0
		  1 = /dev/ip2stat0	Status device for board 0
		  4 = /dev/ip2ipl1	Loadware device for board 1
		  5 = /dev/ip2stat1	Status device for board 1
		  8 = /dev/ip2ipl2	Loadware device for board 2
		  9 = /dev/ip2stat2	Status device for board 2
		 12 = /dev/ip2ipl3	Loadware device for board 3
		 13 = /dev/ip2stat3	Status device for board 3

 74 char	SCI bridge
		  0 = /dev/SCI/0	SCI device 0
		  1 = /dev/SCI/1	SCI device 1
		      ...

		Currently for Dolphin Interconnect Solutions' PCI-SCI
		bridge.

 75 char	Specialix IO8+ serial card
		  0 = /dev/ttyW0	First IO8+ port, first card
		  1 = /dev/ttyW1	Second IO8+ port, first card
		      ...
		  8 = /dev/ttyW8	First IO8+ port, second card
		      ...

 76 char	Specialix IO8+ serial card - alternate devices
		  0 = /dev/cuw0		Callout device corresponding to ttyW0
		  1 = /dev/cuw1		Callout device corresponding to ttyW1
		      ...
		  8 = /dev/cuw8		Callout device corresponding to ttyW8
		      ...

 77 char	ComScire Quantum Noise Generator
		  0 = /dev/qng		ComScire Quantum Noise Generator

 78 char	PAM Software's multimodem boards
		  0 = /dev/ttyM0	First PAM modem
		  1 = /dev/ttyM1	Second PAM modem
		      ...

 79 char	PAM Software's multimodem boards - alternate devices
		  0 = /dev/cum0		Callout device corresponding to ttyM0
		  1 = /dev/cum1		Callout device corresponding to ttyM1
		      ...

 80 char	Photometrics AT200 CCD camera
		  0 = /dev/at200	Photometrics AT200 CCD camera

 81 char	Brooktree Bt848 frame grabbers
		  0 = /dev/bttv0	First Bt848 card
		  1 = /dev/bttv1	Second Bt848 card
		      ...
		 16 = /dev/bttvc0	Control for first Bt848 card
		 17 = /dev/bttvc1	Control for second Bt848 card
		      ...
		 32 = /dev/bttv-vbi0	VBI data of first Bt848 card
		 33 = /dev/bttv-vbi1	VBI data of second Bt848 card
		      ...

 82 char	WiNRADiO communications receiver card
		  0 = /dev/winradio0	First WiNRADiO card
		  1 = /dev/winradio1	Second WiNRADiO card
		      ...

		The driver and documentation may be obtained from
                http://www.proximity.com.au/~brian/winradio/

 83 char	Teletext/videotext interfaces
                  0 = /dev/vtx          Teletext decoder
                 16 = /dev/vttuner      TV tuner on teletext interface

                Devices for the driver contained in the VideoteXt package.
                More information on http://home.pages.de/~videotext/

 84 char	Ikon 1011[57] Versatec Greensheet Interface
                  0 = /dev/ihcp0        First Greensheet port
                  1 = /dev/ihcp1        Second Greensheet port

 85-119		UNALLOCATED

120-127		LOCAL/EXPERIMENTAL USE

128-239		UNALLOCATED

240-254		LOCAL/EXPERIMENTAL USE

255		RESERVED


 ****	ADDITIONAL /dev DIRECTORY ENTRIES

This section details additional entries that should or may exist in
the /dev directory.  It is preferred that symbolic links use the same
form (absolute or relative) as is indicated here.  Links are
classified as "hard" or "symbolic" depending on the preferred type of
link; if possible, the indicated type of link should be used.


	Compulsory links

These links should exist on all systems:

/dev/fd		/proc/self/fd	symbolic	File descriptors
/dev/stdin	fd/0		symbolic	stdin file descriptor
/dev/stdout	fd/1		symbolic	stdout file descriptor
/dev/stderr	fd/2		symbolic	stderr file descriptor
/dev/nfsd	socksys		symbolic	Required by iBCS-2
/dev/X0R	null		symbolic	Required by iBCS-2

Note: the last device is <letter X>-<digit 0>-<letter R>.

	Recommended links

It is recommended that these links exist on all systems:

/dev/core	/proc/kcore	symbolic	Backward compatibility
/dev/ramdisk	ram0		symbolic	Backward compatibility
/dev/ftape	rft0		symbolic	Backward compatibility
/dev/scd?	sr?		hard		Alternate SCSI CD-ROM name


	Locally defined links

The following links may be established locally to conform to the
configuration of the system.  This is merely a tabulation of existing
practice, and does not constitute a recommendation.  However, if they
exist, they should have the following uses.

/dev/mouse	mouse port	symbolic	Current mouse device
/dev/tape	tape device	symbolic	Current tape device
/dev/cdrom	CD-ROM device	symbolic	Current CD-ROM device
/dev/cdwriter	CD-writer	symbolic	Current CD-writer device
/dev/scanner	scanner		symbolic	Current scanner device
/dev/modem	modem port	symbolic	Current dialout device
/dev/root	root device	symbolic	Current root filesystem
/dev/swap	swap device	symbolic	Current swap device

/dev/modem should not be used for a modem which supports dialin as
well as dialout, as it tends to cause lock file problems.  If it
exists, /dev/modem should point to the appropriate dialout (alternate)
device.

For SCSI devices, /dev/tape and /dev/cdrom should point to the
``cooked'' devices (/dev/st* and /dev/sr*, respectively), whereas
/dev/cdwriter and /dev/scanner should point to the appropriate generic
SCSI devices (/dev/sg*).

/dev/mouse may point to a primary serial TTY device, a hardware mouse
device, or a socket for a mouse driver program (e.g. /dev/gpmdata).

	Sockets and pipes

Non-transient sockets and named pipes may exist in /dev.  Common entries are:

/dev/printer	socket		lpd local socket
/dev/log	socket		syslog local socket
/dev/gpmdata	socket		gpm mouse multiplexer


 ****	TERMINAL DEVICES

Terminal, or TTY devices are a special class of character devices.  A
terminal device is any device that could act as a controlling terminal
for a session; this includes virtual consoles, serial ports, and
pseudoterminals (PTYs).

All terminal devices share a common set of capabilities known as line
diciplines; these include the common terminal line dicipline as well
as SLIP and PPP modes.

All terminal devices are named similarly; this section explains the
naming and use of the various types of TTYs.  Note that the naming
conventions include several historical warts; some of these are
Linux-specific, some were inherited from other systems, and some
reflect Linux outgrowing a borrowed convention.

A hash mark (#) in a device name is used here to indicate a decimal
number without leading zeroes.

	Virtual consoles and the console device

Virtual consoles are full-screen terminal displays on the system video
monitor.  Virtual consoles are named /dev/tty#, with numbering
starting at /dev/tty1; /dev/tty0 is the current virtual console.
/dev/tty0 is the device that should be used to access the system video
card on those architectures for which the frame buffer devices
(/dev/fb*) do not exist (including the x86).  Do not use /dev/console
for this purpose.

The console device, /dev/console, is the device to which system
messages should be sent, and on which logins should be permitted in
single-user mode.  /dev/console should be a symbolic link to either
/dev/tty0, a specific virtual console such as /dev/tty1, or to a
serial port primary (tty*, not cu*) device, depending on the
configuration of the system.

	Serial ports

Serial ports are RS-232 serial ports and any device which simulates
one, either in hardware (such as internal modems) or in software (such
as the ISDN driver.)  Under Linux, each serial ports has two device
names, the primary or callin device and the alternate or callout one.
Each kind of device is indicated by a different letter.  For any
letter X, the names of the devices are /dev/ttyX# and /dev/cux#,
respectively; for historical reasons, /dev/ttyS# and /dev/ttyC#
correspond to /dev/cua# and /dev/cub#.  In the future, it should be
expected that multiple letters will be used; all letters will be upper
case for the "tty" device and lower case for the "cu" device.

The names /dev/ttyQ# and /dev/cuq# are reserved for local use.

The alternate devices provide for kernel-based exclusion and somewhat
different defaults than the primary devices.  Their main purpose is to
allow the use of serial ports with programs with no inherent or broken
support for serial ports.  For programs with proper knowledge of
serial port operation, their use should probably be avoided.

Arbitration of serial ports is provided by the use of lock files with
the names /var/lock/LCK..ttyX#.  The contents of the lock file should
be the PID of the locking process as an ASCII number.

It is common practice to install links such as /dev/modem
which point to serial ports.  In order to ensure proper locking in the
presence of these links, it is recommended that software chase
symlinks and lock all possible names; additionally, it is recommended
that a lock file be installed with the corresponding alternate
device.  In order to avoid deadlocks, it is recommended that the locks
are acquired in the following order, and released in the reverse:

	1. The symbolic link name, if any (/var/lock/LCK..modem)
	2. The "tty" name (/var/lock/LCK..ttyS2)
	3. The alternate device name (/var/lock/LCK..cua2)

In the case of nested symbolic links, the lock files should be
installed in the order the symlinks are resolved.

Under no circumstances should an application hold a lock while waiting
for another to be released.  In addition, applications which attempt
to create lock files for the corresponding alternate device names
should take into account the possibility of being used on a non-serial
port TTY, for which no alternate device would exist.

	Pseudoterminals (PTYs)

Pseudoterminals, or PTYs, are used to create login sessions or provide
other capabilities requiring a TTY line dicipline (including SLIP or
PPP capability) to arbitrary data-generation processes.  Each PTY has
a master side, named /dev/pty[p-za-e][0-9a-f], and a slave side, named
/dev/tty[p-za-e][0-9a-f].  The kernel arbitrates the use of PTYs by
allowing each master side to be opened only once.

Once the master side has been opened, the corresponding slave device
can be used in the same manner as any TTY device.  The master and
slave devices are connected by the kernel, generating the equivalent
of a bidirectional pipe with TTY capabilities.

The entire namespace /dev/[pt]ty[p-za-o][0-9a-z] should be considered
reserved for the future use of PTYs.  Should more than 936 PTYs ever
become a necessity, we will likely adopt a System V-like scheme by
which PTYs use a subdirectory of /dev.