The /dev directory

augustoryan

                 The /dev directory
The /dev directory contains
        the special device files for all the devices.
        The device files are created during
        installation, and later with the /dev/MAKEDEV
        script. The /dev/MAKEDEV.local is a script
        written by the system administrator that creates local-only device
        files or links (i.e. those that are not part of the standard
        MAKEDEV, such as device files for some
        non-standard device driver).
This list which follows is by no means exhaustive or as
        detailed as it could be.  Many of these device files will need
        support compiled into your kernel for the hardware.  Read the kernel
        documentation to find details of any particular device.
/dev/dsp
Digital Signal Processor.  Basically this forms
            the interface between software which produces sound and your
            soundcard.  It is a character device on major node 14 and minor
            3.
/dev/fd0
The first floppy drive.  If you are lucky enough
            to have several drives then they will be numbered sequentially.
            It is a character device on major node 2 and minor
            0.
/dev/fb0
The first framebuffer device. A framebuffer is
            an abstraction layer between software and graphics hardware.
            This means that applications do not need to know about what kind
            of hardware you have but merely how to communicate with the
            framebuffer driver's API (Application Programming Interface)
            which is well defined and standardized.  The framebuffer is a
            character device and is on major node 29 and minor
            0.
/dev/hda
/dev/hda is the master IDE
            drive on the primary IDE controller.
            /dev/hdb the slave drive on the
            primary controller.  /dev/hdc
            , and /dev/hdd
             are the master and slave devices
            on the secondary controller respectively.  Each disk is divided
            into partitions. Partitions 1-4 are primary partitions and
            partitions 5 and above are logical partitions inside extended
            partitions.  Therefore the device file which references each
            partition is made up of several parts.  For example
            /dev/hdc9 references partition 9 (a logical
            partition inside an extended partition type) on the master IDE
            drive on the secondary IDE controller.  The major and minor node
            numbers are somewhat complex.  For the first IDE controller all
            partitions are block devices on major node 3.  The master drive
            hda is at minor 0 and the
            slave drive hdb is at minor 64.  For
            each partition inside the drive add the partition number to the minor
            minor node number for the drive.  For example
            /dev/hdb5 is major 3, minor 69 (64 + 5 =
            69). Drives on the secondary interface are handled the same way,
            but with major node 22.
/dev/ht0
The first IDE tape drive.  Subsequent drives are
            numbered ht1 etc.  They are character
            devices on major node 37 and start at minor node 0 for
            ht0 1 for ht1
            etc.
/dev/js0
The first analogue joystick.  Subsequent joysticks
            are numbered js1, js2
            etc.  Digital joysticks are called djs0,
            djs1 and so on.  They are character devices
            on major node 15.  The analogue joysticks start at minor node 0
            and go up to 127 (more than enough for even the most fanatic
            gamer). Digital joysticks start at minor node
            128.
/dev/lp0
The first parallel printer device.  Subsequent
            printers are numbered lp1,
            lp2 etc.  They are character devices on
            major mode 6 and minor nodes starting at 0 and numbered
            sequentially.
/dev/loop0
The first loopback device.  Loopback devices are
            used for mounting filesystems which are not located on other
            block devices such as disks.  For example if you wish to mount
            an iso9660 CD ROM image without burning it to CD then you need
            to use a loopback device to do so.  This is usually transparent
            to the user and is handled by the mount
            
            command.  Refer to the manual pages for mount
            and losetup.
            The loopback devices are block
            devices on major node 7 and with minor nodes starting at 0 and
            numbered sequentially.
/dev/md0
First metadisk group.  Metadisks are related to
            RAID (Redundant Array of Independent Disks) devices.  Please
            refer to the most current RAID HOWTO at the LDP for more details.
            This can be found at
            
            http://www.tldp.org/HOWTO/Software-RAID-HOWTO.html
.
            Metadisk devices are block devices on major node 9 with minor
            nodes starting at 0 and numbered
            sequentially.
/dev/mixer
This is part of the OSS (Open Sound System)
             driver. Refer to the OSS documentation at
http://www.opensound.com
            for more details.  It is a character device on major node 14,
            minor node 0.
/dev/null
The bit bucket.  A black hole where you can send
            data for it never to be seen again.  Anything sent to
            /dev/null will disappear.  This can be
            useful if, for example, you wish to run a command but not have
            any feedback appear on the terminal.  It is a character device
            on major node 1 and minor node 3.
/dev/psaux
The PS/2 mouse port.  This is a character device
            on major node 10, minor node 1.
/dev/pda
Parallel port IDE disks.  These are named
            similarly to disks on the internal IDE controllers
            (/dev/hd*).  They are block devices on major
            node 45. Minor nodes need slightly more explanation here.  The
            first device is /dev/pda and it is on minor
            node 0.  Partitions on this device are found by adding the
            partition number to the minor number for the device.  Each
            device is limited to 15 partitions each rather than 63 (the
            limit for internal IDE disks).  /dev/pdb
            
            minor nodes start at 16, /dev/pdc
             
            at 32 and /dev/pdd at 48.  So for example the
            minor node number for /dev/pdc6 would be 38 (32 +
            6 = 38).  This scheme limits you to 4 parallel disks of 15
            partitions each.
/dev/pcd0
Parallel port CD ROM drives.  These are numbered
            from 0 onwards.  All are block devices on major node 46.
            /dev/pcd0 is on minor node 0 with
            subsequent drives being on minor nodes 1, 2, 3
            etc.
/dev/pt0
Parallel port tape devices.  Tapes do not have
            partitions so these are just numbered sequentially.  They are
            character devices on major node 96.  The minor node numbers
            start from 0 for /dev/pt0, 1 for
            /dev/pt1, and so on.
               
/dev/parport0
The raw parallel ports.  Most devices which are
            attached to parallel ports have their own drivers.  This is a
            device to access the port directly.  It is a character device on
            major node 99 with minor node 0.  Subsequent devices after the
            first are numbered sequentially incrementing the minor
            node.
/dev/random or
            /dev/urandom
These are kernel random number generators.
            /dev/random is a non-deterministic
            generator which means that the value of the next number cannot
            be guessed from the preceding ones.  It uses the entropy of the
            system hardware to generate numbers.  When it has no more
            entropy to use then it must wait until it has collected more
            before it will allow any more numbers to be read from it.
            /dev/urandom works similarly.  Initially it
            also uses the entropy of the system hardware, but when there is
            no more entropy to use it will continue to return numbers using
            a pseudo random number generating formula.  This is considered
            to be less secure for vital purposes such as cryptographic key
            pair generation.  If security is your overriding concern then
            use /dev/random, if speed is more important
            then /dev/urandom works fine.  They are
            character devices on major node 1 with minor nodes 8 for
            /dev/random and 9 for
            /dev/urandom.
/dev/sda
The first SCSI drive on the first SCSI bus.  
            The following drives are named similar to IDE drives.  
            /dev/sdb is the second SCSI drive,
            /dev/sdc is the third SCSI drive, and so
            forth.
/dev/ttyS0
The first serial port.  Many times this it the port used
            to connect an external modem to your system.
/dev/zero
This is a simple way of getting many 0s.  Every
            time you read from this device it will return 0.  This can be
            useful sometimes, for example when you want a file of fixed
            length but don't really care what it contains.  It is a
            character device on major node 1 and minor node
            5.
               
               
               
               
               

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