C.2. Linux Devices
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## C.2. Linux Devices

In Linux you have various special files in `/dev`. These files are called device files. In the Unix world accessing hardware is different. There you have a special file which actually runs a driver which in turn accesses the hardware. The device file is an interface to the actual system component. Files under `/dev` also behave differently than ordinary files. Below are the most important device files listed.

`fd0` | First Floppy Drive
`fd1` | Second Floppy Drive

`hda` | IDE Hard disk / CD-ROM on the first IDE port (Master)
`hdb` | IDE Hard disk / CD-ROM on the first IDE port (Slave)
`hdc` | IDE Hard disk / CD-ROM on the second IDE port (Master)
`hdd` | IDE Hard disk / CD-ROM on the second IDE port (Slave)
`hda1` | First partition of the first IDE hard disk
`hdd15` | Fifteenth partition of the fourth IDE hard disk

`sda` | SCSI Hard disk with lowest SCSI ID (e.g. 0)
`sdb` | SCSI Hard disk with next higher SCSI ID (e.g. 1)
`sdc` | SCSI Hard disk with next higher SCSI ID (e.g. 2)
`sda1` | First partition of the first SCSI hard disk
`sdd10` | Tenth partition of the fourth SCSI hard disk

`sr0` | SCSI CD-ROM with the lowest SCSI ID
`sr1` | SCSI CD-ROM with the next higher SCSI ID

`ttyS0` | Serial port 0, COM1 under MS-DOS
`ttyS1` | Serial port 1, COM2 under MS-DOS
`psaux` | PS/2 mouse device
`gpmdata` | Pseudo device, repeater data from GPM (mouse) daemon

`cdrom` | Symbolic link to the CD-ROM drive
`mouse` | Symbolic link to the mouse device file

`null` | Everything pointed to this device will disappear
`zero` | One can endlessly read zeros out of this device

### C.2.1. Setting Up Your Mouse

The mouse can be used in both the Linux console (with gpm) and the X window environment. The two uses can be made compatible if the gpm repeater is used to allow the signal to flow to the X server as shown:

    mouse => /dev/psaux  => gpm => /dev/gpmdata -> /dev/mouse => X
             /dev/ttyS0             (repeater)        (symlink)
             /dev/ttyS1

Set the repeater protocol to be raw (in `/etc/gpm.conf`) while setting X to the original mouse protocol in `/etc/X11/XF86Config` or `/etc/X11/XF86Config-4`.

This approach to use gpm even in X has advantages when the mouse is unplugged inadvertently. Simply restarting gpm with

    user@debian:# /etc/init.d/gpm restart

will re-connect the mouse in software without restarting X.

If gpm is disabled or not installed with some reason, make sure to set X to read directly from the mouse device such as /dev/psaux. For details, refer to the 3-Button Mouse mini-Howto at `/usr/share/doc/HOWTO/en-txt/mini/3-Button-Mouse.gz`, `man gpm`, `/usr/share/doc/gpm/FAQ.gz`, and README.mouse.

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