Hardware, Devices, and Tools
Knowledge speaks, but wisdom listens.
Jimi Hendrix
This chapter gives an overview of what a device file is, and how to
create one. The canonical list of device files is
/usr/src/linux/Documentation/devices.txt
kerneldevices
if you have
the Linux kernel source code installed on your system. The devices listed
here are correct as of kernel version 2.6.8.
Hardware Utilities
The <command>MAKEDEV</command><indexterm id="ch04-makedev">
<primary>commands</primary><secondary>MAKEDEV</secondary>
</indexterm> Script
Most device files will already be created and will be there
ready to use after you install your Linux system. If by some chance
you need to create one which is not provided then you should first
try to use the MAKEDEV script. This script is
usually located in /dev/MAKEDEV but might also
have a copy (or a symbolic link) in
/sbin/MAKEDEV. If it turns out not to be in
your path then you will need to specify the path to it
explicitly.
In general the command is used as:
# /dev/MAKEDEV -v ttyS0
create ttyS0 c 4 64 root:dialout 0660
This will create the device file /dev/ttyS0
filesystem
/dev/dev/ttyS0
with major node 4 and minor node 64 as a character device with
access permissions 0660 with owner root and group dialout.
ttyS0 is a serial port. The major and
minor node numbers are numbers understood by the kernel. The kernel
refers to hardware devices as numbers, this would be very difficult
for us to remember, so we use filenames. Access permissions of 0660
means read and write permission for the owner (root in this case)
and read and write permission for members of the group (dialout in
this case) with no access for anyone else.
The <command>mknod</command><indexterm id="ch04-mknod">
<primary>commands</primary><secondary>mknod</secondary>
</indexterm> command
MAKEDEV
commandsMAKEDEV
is the preferred way of creating
device files which are not present. However sometimes the
MAKEDEV script will not know about the device
file you wish to create. This is where the mknod
command comes in. In order to use mknod you need
to know the major and minor node numbers for the device you wish to
create. The devices.txt
kerneldocumentation
devices.txt file in the kernel
source documentation is the canonical source of this
information.
To take an example, let us suppose that our version of the
MAKEDEV
commandsMAKEDEV
script does not know how to create the
/dev/ttyS0
filesystem/dev
/dev/ttyS0 device file. We need
to use mknod
commandsmknod
to create it. We know from looking at the
devices.txt
kerneldocumentation
devices.txt that it should be a character
device with major number 4 and minor number 64. So we now know all
we need to create the file.
# mknod /dev/ttyS0 c 4 64
# chown root.dialout /dev/ttyS0
# chmod 0644 /dev/ttyS0
# ls -l /dev/ttyS0
crw-rw---- 1 root dialout 4, 64 Oct 23 18:23 /dev/ttyS0
As you can see, many more steps are required to create the file. In
this example you can see the process required however. It is
unlikely in the extreme that the ttyS0 file would not be provided by
the MAKEDEV
commandsMAKEDEV
script, but it suffices to illustrate
the point.
The <command>lspci</command><indexterm id="ch04-lspci">
<primary>commands</primary><secondary>lspci</secondary>
</indexterm> command
lspci
TO BE ADDED
The <command>lsdev</command><indexterm id="ch04-lsdev">
<primary>commands</primary><secondary>lsdev</secondary>
</indexterm> command
lsdev
TO BE ADDED
The <command>lsusb</command><indexterm id="ch04-lsusb">
<primary>commands</primary><secondary>lsusb</secondary>
</indexterm> command
lsusb
TO BE ADDED
The <command>lsraid</command><indexterm id="ch04-lsraid">
<primary>commands</primary><secondary>lsraid</secondary>
</indexterm> command
lsraid
TO BE ADDED
The <command>hdparm</command><indexterm id="ch04-hdparm">
<primary>commands</primary><secondary>hdparm</secondary>
</indexterm> command
hdparm
TO BE ADDED
More Hardware Resources
More information on what hardware resources the kernel is using
can be found in the /proc directory. Refer to
in chapter 3.
Kernel Modules<indexterm id="ch04-modules"><primary>kernel</primary>
<secondary>modules</secondary></indexterm>
This section will discuss kernel modules.
TO BE ADDED
lsmod<indexterm id="ch04-lsmod1"><primary>commands</primary>
<secondary>lsmod</secondary></indexterm><indexterm id="ch04-lsmod2">
<primary>kernel</primary><secondary>modules</secondary>
<tertiary>lsmod</tertiary></indexterm>
lsmod
TO BE ADDED
insmod<indexterm id="ch04-insmod1"><primary>commands</primary>
<secondary>insmod</secondary></indexterm><indexterm id="ch04-insmod2">
<primary>kernel</primary><secondary>modules</secondary>
<tertiary>insmod</tertiary></indexterm>
insmod
TO BE ADDED
depmod<indexterm id="ch04-depmod1"><primary>commands</primary>
<secondary>depmod</secondary></indexterm><indexterm id="ch04-depmod2">
<primary>kernel</primary><secondary>modules</secondary>
<tertiary>depmod</tertiary></indexterm>
depmod
TO BE ADDED
rmmod<indexterm id="ch04-rmmod1"><primary>commands</primary>
<secondary>rmmod</secondary></indexterm><indexterm id="ch04-rmmod2">
<primary>kernel</primary><secondary>modules</secondary>
<tertiary>rmmod</tertiary></indexterm>
rmmod
TO BE ADDED
modprobe<indexterm id="ch04-modprobe1"><primary>commands</primary>
<secondary>modprobe</secondary></indexterm><indexterm id="ch04-modprobe2">
<primary>kernel</primary><secondary>modules</secondary>
<tertiary>modprobe</tertiary></indexterm>
modprobe
TO BE ADDED