| Advanced Bash-Scripting Guide: A complete guide to shell scripting, using Bash | ||
|---|---|---|
| Prev | Chapter 28. /dev and /proc | Next |
The /dev directory contains entries for the physical devices that may or may not be present in the hardware. [1] The hard drive partitions containing the mounted filesystem(s) have entries in /dev, as a simple df shows.
bash$ df
Filesystem 1k-blocks Used Available Use%
Mounted on
/dev/hda6 495876 222748 247527 48% /
/dev/hda1 50755 3887 44248 9% /boot
/dev/hda8 367013 13262 334803 4% /home
/dev/hda5 1714416 1123624 503704 70% /usr
|
Among other things, the /dev directory also contains loopback devices, such as /dev/loop0. A loopback device is a gimmick allows an ordinary file to be accessed as if it were a block device. [2] This enables mounting an entire filesystem within a single large file. See Example 13-6 and Example 13-5.
A few of the pseudo-devices in /dev have other specialized uses, such as /dev/null, /dev/zero and /dev/urandom.
| [1] |
The entries in /dev provide mount points for physical and virtual devices. These entries use very little drive space. Some devices, such as /dev/null, /dev/zero, and /dev/urandom are virtual. They are not actual physical devices and exist only in software. |
| [2] |
A block device reads and/or writes data in chunks, or blocks, in contrast to a character device, which acesses data in character units. Examples of block devices are a hard drive and CD ROM drive. An example of a character device is a keyboard. |