Red Hat LINUX 7.2 Reference Manual page 65

Section 4.2:Top-Level Files in /proc
162 raw
180 usb
Block devices:
1 ramdisk
2 fd
3 ide0
9 md
22 ide1
The output from /proc/devices includes the major number and name of the device.
Character devices are similar to block devices, except for two basic differences.
First, block devices have a buffer available for requests sent to them, allowing them to order the re-
quests before dealing with them. This comes in very handy with devices designed to store information,
such as hard drives, because the ability to order the information before writing it to the device allows
it to be placed in more efficient order. Character devices do not require this kind of buffering.
Second, block devices can send and receive information in blocks of a particular size, which can be
configured to meet the requirements of the particular device. Character devices send data in as many
or few bytes as they see fit, with no preconfigured size.
To discover if a particular device is a block or character device, type the ls -l <device-name>
command. If the first character in the response is a b, then it is a block device; if it is a c, then it is
character device. For example, note the output from a look at some common devices (hda is the first
IDE hard drive and tty0 is the first terminal port) from the /dev directory:
[root@bleach /]# ls -l /dev/hda /dev/tty0
brw-rw----
crw--w----
[root@bleach /]#
More information about devices can be found in /usr/src/linux-2.4/Documenta-
tion/devices.txt.
4.2.5 /proc/dma
This file contains a list of the registered ISA direct memory access (DMA) channels in use. A sample
/proc/dma files looks like this:
4: cascade
4.2.6 /proc/execdomains
This file lists the execution domains currently supported by the Linux kernel, along with the range of
personalities they support.
1 root disk
1 truk truk
3, 0 Mar 23 23:37 /dev/hda
4, 0 May 3 16:28 /dev/tty0
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