This list is the Linux Device List, the official registry of allocated
device numbers and /dev directory nodes for the Linux operating
system.
The LaTeX version of this document is no longer maintained, nor is the document that used to reside at lanana.org. This version in the mainline Linux kernel is the master document. Updates shall be sent as patches to the kernel maintainers (see the :ref:`Documentation/process/submitting-patches.rst <submittingpatches>` document). Specifically explore the sections titled "CHAR and MISC DRIVERS", and "BLOCK LAYER" in the MAINTAINERS file to find the right maintainers to involve for character and block devices.
This document is included by reference into the Filesystem Hierarchy Standard (FHS). The FHS is available from https://www.pathname.com/fhs/.
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 authors requests, however, that semantically altered versions are not distributed without permission of the authors, assuming the authors can be contacted without an unreasonable effort.
Attention!
DEVICE DRIVERS AUTHORS PLEASE READ THIS
Linux now has extensive support for dynamic allocation of device numbering
and can use sysfs and udev (systemd) to handle the naming needs.
There are still some exceptions in the serial and boot device area. Before
asking for a device number make sure you actually need one.
To have a major number allocated, or a minor number in situations where that applies (e.g. busmice), please submit a patch and send to the authors as indicated above.
Keep the description of the device in the same format as this list. The reason for this is that it is the only way we have found to ensure we have all the requisite information to publish your device and avoid conflicts.
Finally, sometimes we have to play "namespace police." Please don't be
offended. We often get submissions for /dev names that would be bound
to cause conflicts down the road. We are trying to avoid getting in a
situation where we would have to suffer an incompatible forward
change. Therefore, please consult with us before you make your
device names and numbers in any way public, at least to the point
where it would be at all difficult to get them changed.
Your cooperation is appreciated.
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.
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: /dev/X0R is <letter X>-<digit 0>-<letter R>.
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 | qft0 | symbolic | Backward compatibility |
| /dev/bttv0 | video0 | symbolic | Backward compatibility |
| /dev/radio | radio0 | symbolic | Backward compatibility |
| /dev/i2o* | /dev/i2o/* | symbolic | Backward compatibility |
| /dev/scd? | sr? | hard | Alternate SCSI CD-ROM name |
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 primary TTY device
(the use of the alternate callout devices is deprecated).
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).
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 |
The following names are reserved for mounting special filesystems under /dev. These special filesystems provide kernel interfaces that cannot be provided with standard device nodes.
| /dev/pts | devpts | PTY slave filesystem |
| /dev/shm | tmpfs | POSIX shared memory maintenance access |
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 disciplines; these include the common terminal line discipline 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 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*) are not applicable. 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. Starting with Linux 2.1.71, /dev/console is managed
by the kernel; for previous versions it 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 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 (e.g. /dev/ttyDP#) and lower case for the
"cu" device (e.g. /dev/cudp#).
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. Their use is deprecated, and they may be removed from a future version of Linux.
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:
- The symbolic link name, if any (
/var/lock/LCK..modem)- The "tty" name (
/var/lock/LCK..ttyS2)- 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, or PTYs, are used to create login sessions or provide
other capabilities requiring a TTY line discipline (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.
Recent versions of the Linux kernels and GNU libc contain support for
the System V/Unix98 naming scheme for PTYs, which assigns a common
device, /dev/ptmx, to all the masters (opening it will automatically
give you a previously unassigned PTY) and a subdirectory, /dev/pts,
for the slaves; the slaves are named with decimal integers (/dev/pts/#
in our notation). This removes the problem of exhausting the
namespace and enables the kernel to automatically create the device
nodes for the slaves on demand using the "devpts" filesystem.