1 .. _admin_devices:
2
3 Linux allocated devices (4.x+ version)
4 ======================================
5
6 This list is the Linux Device List, the offici
7 device numbers and ``/dev`` directory nodes fo
8 system.
9
10 The version of this document at lanana.org is
11 version in the mainline Linux kernel is the ma
12 shall be sent as patches to the kernel maintai
13 :ref:`Documentation/process/submitting-patches
14 Specifically explore the sections titled "CHAR
15 "BLOCK LAYER" in the MAINTAINERS file to find
16 to involve for character and block devices.
17
18 This document is included by reference into th
19 Standard (FHS). The FHS is available from htt
20
21 Allocations marked (68k/Amiga) apply to Linux/
22 platform only. Allocations marked (68k/Atari)
23 the Atari platform only.
24
25 This document is in the public domain. The au
26 that semantically altered versions are not dis
27 permission of the authors, assuming the author
28 an unreasonable effort.
29
30
31 .. attention::
32
33 DEVICE DRIVERS AUTHORS PLEASE READ THIS
34
35 Linux now has extensive support for dynamic
36 and can use ``sysfs`` and ``udev`` (``system
37 There are still some exceptions in the seria
38 asking for a device number make sure you a
39
40 To have a major number allocated, or a minor
41 where that applies (e.g. busmice), please su
42 the authors as indicated above.
43
44 Keep the description of the device *in the s
45 as this list*. The reason for this is that i
46 found to ensure we have all the requisite in
47 device and avoid conflicts.
48
49 Finally, sometimes we have to play "namespac
50 offended. We often get submissions for ``/d
51 to cause conflicts down the road. We are tr
52 situation where we would have to suffer an i
53 change. Therefore, please consult with us *
54 device names and numbers in any way public,
55 where it would be at all difficult to get th
56
57 Your cooperation is appreciated.
58
59 .. include:: devices.txt
60 :literal:
61
62 Additional ``/dev/`` directory entries
63 --------------------------------------
64
65 This section details additional entries that s
66 the /dev directory. It is preferred that symb
67 form (absolute or relative) as is indicated he
68 classified as "hard" or "symbolic" depending o
69 link; if possible, the indicated type of link
70
71 Compulsory links
72 ++++++++++++++++
73
74 These links should exist on all systems:
75
76 =============== =============== ==============
77 /dev/fd /proc/self/fd symbolic
78 /dev/stdin fd/0 symbolic
79 /dev/stdout fd/1 symbolic
80 /dev/stderr fd/2 symbolic
81 /dev/nfsd socksys symbolic
82 /dev/X0R null symbolic
83 =============== =============== ==============
84
85 Note: ``/dev/X0R`` is <letter X>-<digit 0>-<le
86
87 Recommended links
88 +++++++++++++++++
89
90 It is recommended that these links exist on al
91
92
93 =============== =============== ==============
94 /dev/core /proc/kcore symbolic
95 /dev/ramdisk ram0 symbolic
96 /dev/ftape qft0 symbolic
97 /dev/bttv0 video0 symbolic
98 /dev/radio radio0 symbolic
99 /dev/i2o* /dev/i2o/* symbolic
100 /dev/scd? sr? hard
101 =============== =============== ==============
102
103 Locally defined links
104 +++++++++++++++++++++
105
106 The following links may be established locally
107 configuration of the system. This is merely a
108 practice, and does not constitute a recommenda
109 exist, they should have the following uses.
110
111 =============== =============== ==============
112 /dev/mouse mouse port symbolic
113 /dev/tape tape device symbolic
114 /dev/cdrom CD-ROM device symbolic
115 /dev/cdwriter CD-writer symbolic
116 /dev/scanner scanner symbolic
117 /dev/modem modem port symbolic
118 /dev/root root device symbolic
119 /dev/swap swap device symbolic
120 =============== =============== ==============
121
122 ``/dev/modem`` should not be used for a modem
123 well as dialout, as it tends to cause lock fil
124 exists, ``/dev/modem`` should point to the app
125 (the use of the alternate callout devices is d
126
127 For SCSI devices, ``/dev/tape`` and ``/dev/cdr
128 *cooked* devices (``/dev/st*`` and ``/dev/sr*`
129 ``/dev/cdwriter`` and /dev/scanner should poin
130 SCSI devices (/dev/sg*).
131
132 ``/dev/mouse`` may point to a primary serial T
133 device, or a socket for a mouse driver program
134
135 Sockets and pipes
136 +++++++++++++++++
137
138 Non-transient sockets and named pipes may exis
139
140 =============== =============== ==============
141 /dev/printer socket lpd local sock
142 /dev/log socket syslog local s
143 /dev/gpmdata socket gpm mouse mult
144 =============== =============== ==============
145
146 Mount points
147 ++++++++++++
148
149 The following names are reserved for mounting
150 under /dev. These special filesystems provide
151 cannot be provided with standard device nodes.
152
153 =============== =============== ==============
154 /dev/pts devpts PTY slave file
155 /dev/shm tmpfs POSIX shared m
156 =============== =============== ==============
157
158 Terminal devices
159 ----------------
160
161 Terminal, or TTY devices are a special class o
162 terminal device is any device that could act a
163 for a session; this includes virtual consoles,
164 pseudoterminals (PTYs).
165
166 All terminal devices share a common set of cap
167 disciplines; these include the common terminal
168 as SLIP and PPP modes.
169
170 All terminal devices are named similarly; this
171 naming and use of the various types of TTYs.
172 conventions include several historical warts;
173 Linux-specific, some were inherited from other
174 reflect Linux outgrowing a borrowed convention
175
176 A hash mark (``#``) in a device name is used h
177 number without leading zeroes.
178
179 Virtual consoles and the console device
180 +++++++++++++++++++++++++++++++++++++++
181
182 Virtual consoles are full-screen terminal disp
183 monitor. Virtual consoles are named ``/dev/tt
184 starting at ``/dev/tty1``; ``/dev/tty0`` is th
185 ``/dev/tty0`` is the device that should be use
186 card on those architectures for which the fram
187 (``/dev/fb*``) are not applicable. Do not use
188 for this purpose.
189
190 The console device, ``/dev/console``, is the d
191 messages should be sent, and on which logins s
192 single-user mode. Starting with Linux 2.1.71,
193 by the kernel; for previous versions it should
194 either ``/dev/tty0``, a specific virtual conso
195 a serial port primary (``tty*``, not ``cu*``)
196 configuration of the system.
197
198 Serial ports
199 ++++++++++++
200
201 Serial ports are RS-232 serial ports and any d
202 one, either in hardware (such as internal mode
203 as the ISDN driver.) Under Linux, each serial
204 names, the primary or callin device and the al
205 Each kind of device is indicated by a differen
206 letter X, the names of the devices are ``/dev/
207 respectively; for historical reasons, ``/dev/t
208 correspond to ``/dev/cua#`` and ``/dev/cub#``.
209 expected that multiple letters will be used; a
210 case for the "tty" device (e.g. ``/dev/ttyDP#`
211 "cu" device (e.g. ``/dev/cudp#``).
212
213 The names ``/dev/ttyQ#`` and ``/dev/cuq#`` are
214
215 The alternate devices provide for kernel-based
216 different defaults than the primary devices.
217 allow the use of serial ports with programs wi
218 support for serial ports. Their use is deprec
219 removed from a future version of Linux.
220
221 Arbitration of serial ports is provided by the
222 the names ``/var/lock/LCK..ttyX#``. The conten
223 be the PID of the locking process as an ASCII
224
225 It is common practice to install links such as
226 which point to serial ports. In order to ensu
227 presence of these links, it is recommended tha
228 symlinks and lock all possible names; addition
229 that a lock file be installed with the corresp
230 device. In order to avoid deadlocks, it is re
231 are acquired in the following order, and relea
232
233 1. The symbolic link name, if any (``/
234 2. The "tty" name (``/var/lock/LCK..tt
235 3. The alternate device name (``/var/l
236
237 In the case of nested symbolic links, the lock
238 installed in the order the symlinks are resolv
239
240 Under no circumstances should an application h
241 for another to be released. In addition, appl
242 to create lock files for the corresponding alt
243 should take into account the possibility of be
244 port TTY, for which no alternate device would
245
246 Pseudoterminals (PTYs)
247 ++++++++++++++++++++++
248
249 Pseudoterminals, or PTYs, are used to create l
250 other capabilities requiring a TTY line discip
251 PPP capability) to arbitrary data-generation p
252 a master side, named ``/dev/pty[p-za-e][0-9a-f
253 ``/dev/tty[p-za-e][0-9a-f]``. The kernel arbi
254 allowing each master side to be opened only on
255
256 Once the master side has been opened, the corr
257 can be used in the same manner as any TTY devi
258 slave devices are connected by the kernel, gen
259 of a bidirectional pipe with TTY capabilities.
260
261 Recent versions of the Linux kernels and GNU l
262 the System V/Unix98 naming scheme for PTYs, wh
263 device, ``/dev/ptmx``, to all the masters (ope
264 give you a previously unassigned PTY) and a su
265 for the slaves; the slaves are named with deci
266 in our notation). This removes the problem of
267 namespace and enables the kernel to automatica
268 nodes for the slaves on demand using the "devp
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