1 2Linux allocated devices (4.x+ version) 3====================================== 4 5This list is the Linux Device List, the official registry of allocated 6device numbers and ``/dev`` directory nodes for the Linux operating 7system. 8 9The LaTeX version of this document is no longer maintained, nor is 10the document that used to reside at lanana.org. This version in the 11mainline Linux kernel is the master document. Updates shall be sent 12as patches to the kernel maintainers (see the 13:ref:`Documentation/process/submitting-patches.rst <submittingpatches>` document). 14Specifically explore the sections titled "CHAR and MISC DRIVERS", and 15"BLOCK LAYER" in the MAINTAINERS file to find the right maintainers 16to involve for character and block devices. 17 18This document is included by reference into the Filesystem Hierarchy 19Standard (FHS). The FHS is available from http://www.pathname.com/fhs/. 20 21Allocations marked (68k/Amiga) apply to Linux/68k on the Amiga 22platform only. Allocations marked (68k/Atari) apply to Linux/68k on 23the Atari platform only. 24 25This document is in the public domain. The authors requests, however, 26that semantically altered versions are not distributed without 27permission of the authors, assuming the authors can be contacted without 28an unreasonable effort. 29 30 31.. attention:: 32 33 DEVICE DRIVERS AUTHORS PLEASE READ THIS 34 35 Linux now has extensive support for dynamic allocation of device numbering 36 and can use ``sysfs`` and ``udev`` (``systemd``) to handle the naming needs. 37 There are still some exceptions in the serial and boot device area. Before 38 asking for a device number make sure you actually need one. 39 40 To have a major number allocated, or a minor number in situations 41 where that applies (e.g. busmice), please submit a patch and send to 42 the authors as indicated above. 43 44 Keep the description of the device *in the same format 45 as this list*. The reason for this is that it is the only way we have 46 found to ensure we have all the requisite information to publish your 47 device and avoid conflicts. 48 49 Finally, sometimes we have to play "namespace police." Please don't be 50 offended. We often get submissions for ``/dev`` names that would be bound 51 to cause conflicts down the road. We are trying to avoid getting in a 52 situation where we would have to suffer an incompatible forward 53 change. Therefore, please consult with us **before** you make your 54 device names and numbers in any way public, at least to the point 55 where it would be at all difficult to get them changed. 56 57 Your cooperation is appreciated. 58 59.. include:: devices.txt 60 :literal: 61 62Additional ``/dev/`` directory entries 63-------------------------------------- 64 65This section details additional entries that should or may exist in 66the /dev directory. It is preferred that symbolic links use the same 67form (absolute or relative) as is indicated here. Links are 68classified as "hard" or "symbolic" depending on the preferred type of 69link; if possible, the indicated type of link should be used. 70 71Compulsory links 72++++++++++++++++ 73 74These links should exist on all systems: 75 76=============== =============== =============== =============================== 77/dev/fd /proc/self/fd symbolic File descriptors 78/dev/stdin fd/0 symbolic stdin file descriptor 79/dev/stdout fd/1 symbolic stdout file descriptor 80/dev/stderr fd/2 symbolic stderr file descriptor 81/dev/nfsd socksys symbolic Required by iBCS-2 82/dev/X0R null symbolic Required by iBCS-2 83=============== =============== =============== =============================== 84 85Note: ``/dev/X0R`` is <letter X>-<digit 0>-<letter R>. 86 87Recommended links 88+++++++++++++++++ 89 90It is recommended that these links exist on all systems: 91 92 93=============== =============== =============== =============================== 94/dev/core /proc/kcore symbolic Backward compatibility 95/dev/ramdisk ram0 symbolic Backward compatibility 96/dev/ftape qft0 symbolic Backward compatibility 97/dev/bttv0 video0 symbolic Backward compatibility 98/dev/radio radio0 symbolic Backward compatibility 99/dev/i2o* /dev/i2o/* symbolic Backward compatibility 100/dev/scd? sr? hard Alternate SCSI CD-ROM name 101=============== =============== =============== =============================== 102 103Locally defined links 104+++++++++++++++++++++ 105 106The following links may be established locally to conform to the 107configuration of the system. This is merely a tabulation of existing 108practice, and does not constitute a recommendation. However, if they 109exist, they should have the following uses. 110 111=============== =============== =============== =============================== 112/dev/mouse mouse port symbolic Current mouse device 113/dev/tape tape device symbolic Current tape device 114/dev/cdrom CD-ROM device symbolic Current CD-ROM device 115/dev/cdwriter CD-writer symbolic Current CD-writer device 116/dev/scanner scanner symbolic Current scanner device 117/dev/modem modem port symbolic Current dialout device 118/dev/root root device symbolic Current root filesystem 119/dev/swap swap device symbolic Current swap device 120=============== =============== =============== =============================== 121 122``/dev/modem`` should not be used for a modem which supports dialin as 123well as dialout, as it tends to cause lock file problems. If it 124exists, ``/dev/modem`` should point to the appropriate primary TTY device 125(the use of the alternate callout devices is deprecated). 126 127For SCSI devices, ``/dev/tape`` and ``/dev/cdrom`` should point to the 128*cooked* devices (``/dev/st*`` and ``/dev/sr*``, respectively), whereas 129``/dev/cdwriter`` and /dev/scanner should point to the appropriate generic 130SCSI devices (/dev/sg*). 131 132``/dev/mouse`` may point to a primary serial TTY device, a hardware mouse 133device, or a socket for a mouse driver program (e.g. ``/dev/gpmdata``). 134 135Sockets and pipes 136+++++++++++++++++ 137 138Non-transient sockets and named pipes may exist in /dev. Common entries are: 139 140=============== =============== =============================================== 141/dev/printer socket lpd local socket 142/dev/log socket syslog local socket 143/dev/gpmdata socket gpm mouse multiplexer 144=============== =============== =============================================== 145 146Mount points 147++++++++++++ 148 149The following names are reserved for mounting special filesystems 150under /dev. These special filesystems provide kernel interfaces that 151cannot be provided with standard device nodes. 152 153=============== =============== =============================================== 154/dev/pts devpts PTY slave filesystem 155/dev/shm tmpfs POSIX shared memory maintenance access 156=============== =============== =============================================== 157 158Terminal devices 159---------------- 160 161Terminal, or TTY devices are a special class of character devices. A 162terminal device is any device that could act as a controlling terminal 163for a session; this includes virtual consoles, serial ports, and 164pseudoterminals (PTYs). 165 166All terminal devices share a common set of capabilities known as line 167disciplines; these include the common terminal line discipline as well 168as SLIP and PPP modes. 169 170All terminal devices are named similarly; this section explains the 171naming and use of the various types of TTYs. Note that the naming 172conventions include several historical warts; some of these are 173Linux-specific, some were inherited from other systems, and some 174reflect Linux outgrowing a borrowed convention. 175 176A hash mark (``#``) in a device name is used here to indicate a decimal 177number without leading zeroes. 178 179Virtual consoles and the console device 180+++++++++++++++++++++++++++++++++++++++ 181 182Virtual consoles are full-screen terminal displays on the system video 183monitor. Virtual consoles are named ``/dev/tty#``, with numbering 184starting at ``/dev/tty1``; ``/dev/tty0`` is the current virtual console. 185``/dev/tty0`` is the device that should be used to access the system video 186card on those architectures for which the frame buffer devices 187(``/dev/fb*``) are not applicable. Do not use ``/dev/console`` 188for this purpose. 189 190The console device, ``/dev/console``, is the device to which system 191messages should be sent, and on which logins should be permitted in 192single-user mode. Starting with Linux 2.1.71, ``/dev/console`` is managed 193by the kernel; for previous versions it should be a symbolic link to 194either ``/dev/tty0``, a specific virtual console such as ``/dev/tty1``, or to 195a serial port primary (``tty*``, not ``cu*``) device, depending on the 196configuration of the system. 197 198Serial ports 199++++++++++++ 200 201Serial ports are RS-232 serial ports and any device which simulates 202one, either in hardware (such as internal modems) or in software (such 203as the ISDN driver.) Under Linux, each serial ports has two device 204names, the primary or callin device and the alternate or callout one. 205Each kind of device is indicated by a different letter. For any 206letter X, the names of the devices are ``/dev/ttyX#`` and ``/dev/cux#``, 207respectively; for historical reasons, ``/dev/ttyS#`` and ``/dev/ttyC#`` 208correspond to ``/dev/cua#`` and ``/dev/cub#``. In the future, it should be 209expected that multiple letters will be used; all letters will be upper 210case for the "tty" device (e.g. ``/dev/ttyDP#``) and lower case for the 211"cu" device (e.g. ``/dev/cudp#``). 212 213The names ``/dev/ttyQ#`` and ``/dev/cuq#`` are reserved for local use. 214 215The alternate devices provide for kernel-based exclusion and somewhat 216different defaults than the primary devices. Their main purpose is to 217allow the use of serial ports with programs with no inherent or broken 218support for serial ports. Their use is deprecated, and they may be 219removed from a future version of Linux. 220 221Arbitration of serial ports is provided by the use of lock files with 222the names ``/var/lock/LCK..ttyX#``. The contents of the lock file should 223be the PID of the locking process as an ASCII number. 224 225It is common practice to install links such as /dev/modem 226which point to serial ports. In order to ensure proper locking in the 227presence of these links, it is recommended that software chase 228symlinks and lock all possible names; additionally, it is recommended 229that a lock file be installed with the corresponding alternate 230device. In order to avoid deadlocks, it is recommended that the locks 231are acquired in the following order, and released in the reverse: 232 233 1. The symbolic link name, if any (``/var/lock/LCK..modem``) 234 2. The "tty" name (``/var/lock/LCK..ttyS2``) 235 3. The alternate device name (``/var/lock/LCK..cua2``) 236 237In the case of nested symbolic links, the lock files should be 238installed in the order the symlinks are resolved. 239 240Under no circumstances should an application hold a lock while waiting 241for another to be released. In addition, applications which attempt 242to create lock files for the corresponding alternate device names 243should take into account the possibility of being used on a non-serial 244port TTY, for which no alternate device would exist. 245 246Pseudoterminals (PTYs) 247++++++++++++++++++++++ 248 249Pseudoterminals, or PTYs, are used to create login sessions or provide 250other capabilities requiring a TTY line discipline (including SLIP or 251PPP capability) to arbitrary data-generation processes. Each PTY has 252a master side, named ``/dev/pty[p-za-e][0-9a-f]``, and a slave side, named 253``/dev/tty[p-za-e][0-9a-f]``. The kernel arbitrates the use of PTYs by 254allowing each master side to be opened only once. 255 256Once the master side has been opened, the corresponding slave device 257can be used in the same manner as any TTY device. The master and 258slave devices are connected by the kernel, generating the equivalent 259of a bidirectional pipe with TTY capabilities. 260 261Recent versions of the Linux kernels and GNU libc contain support for 262the System V/Unix98 naming scheme for PTYs, which assigns a common 263device, ``/dev/ptmx``, to all the masters (opening it will automatically 264give you a previously unassigned PTY) and a subdirectory, ``/dev/pts``, 265for the slaves; the slaves are named with decimal integers (``/dev/pts/#`` 266in our notation). This removes the problem of exhausting the 267namespace and enables the kernel to automatically create the device 268nodes for the slaves on demand using the "devpts" filesystem. 269