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<!--Table of Child-Links-->
<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></A>

<UL>
<LI><A NAME="tex2html2064"
  HREF="#SECTION002110000000000000000">18.1 Device Files</A>
<LI><A NAME="tex2html2065"
  HREF="#SECTION002120000000000000000">18.2 Block and Character Devices</A>
<LI><A NAME="tex2html2066"
  HREF="#SECTION002130000000000000000">18.3 <I>Major</I> and <I>Minor</I> Device Numbers</A>
<LI><A NAME="tex2html2067"
  HREF="#SECTION002140000000000000000">18.4 Common Device Names</A>
<LI><A NAME="tex2html2068"
  HREF="#SECTION002150000000000000000">18.5 <TT>
<FONT COLOR="#0000ff">dd</FONT></TT>, <TT>
<FONT COLOR="#0000ff">tar</FONT></TT>, and Tricks with Block Devices</A>
<UL>
<LI><A NAME="tex2html2069"
  HREF="#SECTION002151000000000000000">18.5.1 Creating boot disks from boot images</A>
<LI><A NAME="tex2html2070"
  HREF="#SECTION002152000000000000000">18.5.2 Erasing disks</A>
<LI><A NAME="tex2html2071"
  HREF="#SECTION002153000000000000000">18.5.3 Identifying data on raw disks</A>
<LI><A NAME="tex2html2072"
  HREF="#SECTION002154000000000000000">18.5.4 Duplicating a disk</A>
<LI><A NAME="tex2html2073"
  HREF="#SECTION002155000000000000000">18.5.5 Backing up to floppies</A>
<LI><A NAME="tex2html2074"
  HREF="#SECTION002156000000000000000">18.5.6 Tape backups</A>
<LI><A NAME="tex2html2075"
  HREF="#SECTION002157000000000000000">18.5.7 Hiding program output, creating blocks of zeros</A>
</UL>
<LI><A NAME="tex2html2076"
  HREF="#SECTION002160000000000000000">18.6 Creating Devices with <TT>
<FONT COLOR="#0000ff">mknod</FONT></TT> and <TT>
<FONT COLOR="#0000ff">/dev/MAKEDEV</FONT></TT></A>
</UL>
<!--End of Table of Child-Links-->
<HR>

<H1><A NAME="SECTION002100000000000000000">
18. U<SMALL>NIX</SMALL> Devices</A>
</H1>

<P>
<A NAME="chap:unixdevices"></A>
<P>
U<SMALL>NIX</SMALL> was designed to allow transparent access to hardware devices
across all CPU architectures. U<SMALL>NIX</SMALL> also supports the philosophy that
all devices be accessible using the same set of command-line
utilities.

<P>

<H1><A NAME="SECTION002110000000000000000">
18.1 Device Files</A>
</H1>

<P>
<A NAME="chap:device"></A>
<P>
U<SMALL>NIX</SMALL> has a beautifully consistent method of allowing programs to
access hardware. Under U<SMALL>NIX</SMALL>, every piece of hardware is a file. To
demonstrate this novelty, try viewing the file <TT>
<FONT COLOR="#0000ff">/dev/hda</FONT></TT> (you will have to
be <TT>
<FONT COLOR="#0000ff">root</FONT></TT> to run this command):

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>less&nbsp;-f&nbsp;/dev/hda</code><br>
</FONT></TD></TR></TABLE><P>
<TT>
<FONT COLOR="#0000ff">/dev/hda</FONT></TT> is not really a file at all. When you read
from it, you are actually reading directly from the first
physical hard disk of your machine. <TT>
<FONT COLOR="#0000ff">/dev/hda</FONT></TT> is known
as a device file, and all of them are stored under the
<TT>
<FONT COLOR="#0000ff">/dev</FONT></TT> directory.

<P>
Device files allow access to hardware. If you have a sound card installed
and configured, you can try:

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>cat&nbsp;/dev/dsp&nbsp;&#062;&nbsp;my_recording</code><br>
</FONT></TD></TR></TABLE><P>
Say something into your microphone and then type:

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>cat&nbsp;my_recording&nbsp;&#062;&nbsp;/dev/dsp</code><br>
</FONT></TD></TR></TABLE><P>
The system will play out the sound through your speakers. (Note that
this does not always work, since the recording volume or the recording
speed may not be set correctly.)

<P>
If no programs are currently using your mouse, you can also try:

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>cat&nbsp;/dev/mouse</code><br>
</FONT></TD></TR></TABLE><P>
If you now move the mouse, the mouse protocol commands will be
written directly to your screen (it will look like garbage).
This is an easy way to see if your mouse is working, and is especially
useful for testing a serial port.
Occasionally this test doesn't work because some command has previously
configured the serial port in some odd way. In that case, also try:

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>cu&nbsp;-s&nbsp;1200&nbsp;-l&nbsp;/dev/mouse</code><br>
</FONT></TD></TR></TABLE><P>

<P>
At a lower level, programs that access device files do so in
two basic ways:

<UL>
<LI>They read and write to the device to send and retrieve
bulk data (much like <TT>
<FONT COLOR="#0000ff">less</FONT></TT> and <TT>
<FONT COLOR="#0000ff">cat</FONT></TT> above).
</LI>
<LI>They use the <B>C</B> <TT>
<FONT COLOR="#0000ff">ioctl</FONT></TT> (<I>IO Control</I>) function
to configure the device. (In the case of the sound card, this
might set mono versus stereo, recording speed, or other parameters.)
</LI>
</UL>

<P>
Because every kind of device that one can think of (except
for network cards) can be twisted to fit these two modes
of operation, U<SMALL>NIX</SMALL>'s scheme has endured since its inception
and is the universal method of accessing hardware.

<P>

<H1><A NAME="SECTION002120000000000000000">
18.2 Block and Character Devices</A>
</H1>

<P>
Hardware devices can generally be categorized into
random access devices
like disk and tape drives, and serial devices like mouse
devices, sound cards, and terminals.

<P>
Random access devices are usually accessed in large contiguous
blocks of data that are stored persistently. They are read from
in discrete units (for most disks, 1024 bytes at a time). These
are known as <I>block</I> devices. Running an <TT>
<FONT COLOR="#0000ff">ls -l /dev/hda</FONT></TT> shows
a <TT>
<FONT COLOR="#0000ff">b</FONT></TT> on the far left of the listing, which means that your hard disk
is a block device:

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>brw-r-----&nbsp;&nbsp;&nbsp;1&nbsp;root&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;disk&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3,&nbsp;&nbsp;64&nbsp;Apr&nbsp;27&nbsp;&nbsp;1995&nbsp;/dev/hdb</code><br>
</FONT></TD></TR></TABLE><P>

<P>
Serial devices, on the other hand, are accessed one byte at a
time. Data can be read or written only once. For example, after
a byte has been read from your mouse, the same byte cannot be
read by some other program. Serial devices are called <I>character</I>
devices and are indicated by a <TT>
<FONT COLOR="#0000ff">c</FONT></TT> on the far left of the
listing. Your <TT>
<FONT COLOR="#0000ff">/dev/dsp</FONT></TT> (<I>Digital
Signal Processor</I>--that is, your sound card) device looks like:

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>crw-r--r--&nbsp;&nbsp;&nbsp;1&nbsp;root&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sys&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;14,&nbsp;&nbsp;&nbsp;3&nbsp;Jul&nbsp;18&nbsp;&nbsp;1994&nbsp;/dev/dsp</code><br>
</FONT></TD></TR></TABLE><P>

<P>

<H1><A NAME="SECTION002130000000000000000">
18.3 <I>Major</I> and <I>Minor</I> Device Numbers</A>
</H1>

<P>
Devices are divided into sets called <I>major device numbers</I>.
For instance, all SCSI disks are <I>major number
8</I>. Further, each individual device has a <I>minor device number</I>
like <TT>
<FONT COLOR="#0000ff">/dev/sda</FONT></TT>, which is <I>minor device 0</I>.
Major and minor device numbers identify the device
to the kernel. The file name of the device is arbitrary
and is chosen for convenience and consistency. You can see the
major and minor device number (<TT>
<FONT COLOR="#0000ff">8,&nbsp;&nbsp;&nbsp;0</FONT></TT>) in the
<TT>
<FONT COLOR="#0000ff">ls</FONT></TT> listing for
<TT>
<FONT COLOR="#0000ff">/dev/sda</FONT></TT>:

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>brw-rw----&nbsp;&nbsp;&nbsp;1&nbsp;root&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;disk&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;8,&nbsp;&nbsp;&nbsp;0&nbsp;May&nbsp;&nbsp;5&nbsp;&nbsp;1998&nbsp;/dev/sda</code><br>
</FONT></TD></TR></TABLE><P>

<P>

<H1><A NAME="SECTION002140000000000000000">
18.4 Common Device Names</A>
</H1>

<P>
<A NAME="sec:miscdevices"></A>
<P>
A list of common devices and their descriptions follows.
The major numbers are shown in parentheses. The complete reference
for devices is the file
<TT>
<FONT COLOR="#0000ff">/usr/src/linux/Documentation/devices.txt</FONT></TT>.

<P>
<DL>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/hd??</FONT></TT></STRONG></DT>
<DD><TT>
<FONT COLOR="#0000ff">hd</FONT></TT> stands for <I>hard disk</I>, but refers here only to
<I>IDE</I> devices--that is, common hard
disks. The first letter after the <TT>
<FONT COLOR="#0000ff">hd</FONT></TT> dictates the physical disk drive:
<DL>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/hda</FONT></TT> (3)</STRONG></DT>
<DD>First drive, or primary master.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/hdb</FONT></TT> (3)</STRONG></DT>
<DD>Second drive, or primary slave.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/hdc</FONT></TT> (22)</STRONG></DT>
<DD>Third drive, or secondary master.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/hdd</FONT></TT> (22)</STRONG></DT>
<DD>Fourth drive, or secondary slave.
</DD>
</DL>
When accessing any of these devices (with, say, <TT>
<FONT COLOR="#0000ff">less /dev/hda</FONT></TT>), you
would be reading raw from the actual physical disk starting at the
first sector of the first track,
sequentially, until the last sector of the last
track.

<P>
Partitions<A NAME="page:partition"></A> <FONT COLOR="#ffa500">[With all operating systems, disk
drives are divided into sections called <I>partitions</I>. A typical disk might
have 2 to 10 partitions. Each partition acts as a whole disk on its own,
giving the effect of having more than one disk. For instance, you might
have Windows installed on one partition
and L<SMALL>INUX</SMALL> installed on another.
More details come in Chapter <A HREF="node22.html#chap:partfilesys">19</A>.]</FONT>are named <TT>
<FONT COLOR="#0000ff">/dev/hda1</FONT></TT>, <TT>
<FONT COLOR="#0000ff">/dev/hda2</FONT></TT>,
etc., indicating the first, second, etc., partition on physical
drive <TT>
<FONT COLOR="#0000ff">a</FONT></TT>.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/sd</FONT></TT><I>??</I> (8)</STRONG></DT>
<DD><TT>
<FONT COLOR="#0000ff">sd</FONT></TT> stands for <I>SCSI disk</I>,
the high-end drives mostly used by servers. <TT>
<FONT COLOR="#0000ff">sda</FONT></TT> is the
first physical disk probed, and so on. Probing goes by SCSI ID
and has a system completely different from that of IDE devices. <TT>
<FONT COLOR="#0000ff">/dev/sda1</FONT></TT>
is the first partition on the first drive, etc.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/ttyS</FONT></TT><I>?</I> (4)</STRONG></DT>
<DD>These are serial devices numbered from
<TT>
<FONT COLOR="#0000ff">0</FONT></TT> up. <TT>
<FONT COLOR="#0000ff">/dev/ttyS0</FONT></TT> is your first serial port (COM1 under MS-DOS or Windows).
If you have a multiport card, these can go to <TT>
<FONT COLOR="#0000ff">32</FONT></TT>, <TT>
<FONT COLOR="#0000ff">64</FONT></TT>, and up.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/psaux</FONT></TT> (10)</STRONG></DT>
<DD>PS/2 mouse.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/mouse</FONT></TT></STRONG></DT>
<DD>A symlink to <TT>
<FONT COLOR="#0000ff">/dev/ttyS0</FONT></TT> or <TT>
<FONT COLOR="#0000ff">/dev/psaux</FONT></TT>.
Other mouse devices are also supported.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/modem</FONT></TT></STRONG></DT>
<DD>A symlink to <TT>
<FONT COLOR="#0000ff">/dev/ttyS1</FONT></TT> or whatever port your
modem is on.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/cua</FONT></TT><I>?</I> (4)</STRONG></DT>
<DD>Identical to <TT>
<FONT COLOR="#0000ff">ttyS</FONT></TT><I>?</I> but now fallen out of use.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/fd</FONT></TT><I>?</I> (2)</STRONG></DT>
<DD><I>Floppy disk</I>. <TT>
<FONT COLOR="#0000ff">fd0</FONT></TT>
is equivalent to your <TT>
<FONT COLOR="#0000ff">A:</FONT></TT> drive and <TT>
<FONT COLOR="#0000ff">fd1</FONT></TT> your
<TT>
<FONT COLOR="#0000ff">B:</FONT></TT> drive. The <TT>
<FONT COLOR="#0000ff">fd0</FONT></TT> and <TT>
<FONT COLOR="#0000ff">fd1</FONT></TT> devices
autodetect the format of the floppy disk, but you can
explicitly specify a higher density by using a device name like
<TT>
<FONT COLOR="#0000ff">/dev/fd0H1920</FONT></TT>, which gives you access to 1.88 MB,
formatted, 3.5-inch floppies. Other floppy devices are shown in
Table <A HREF="node21.html#tab:floppydevicenaming">18.1</A>.

<P>
See Section&nbsp;<A HREF="node22.html#sec:floppyformat">19.3.4</A> on how to format these devices.

<P>
<BR><P></P>
<DIV ALIGN="CENTER"><A NAME="tab:floppydevicenaming"></A><A NAME="page:floppydevice"></A><A NAME="24189"></A>
<TABLE>
<CAPTION><STRONG>Table 18.1:</STRONG>
Floppy device names</CAPTION>
<TR><TD><IMG
 WIDTH="556" HEIGHT="408" BORDER="0"
 SRC="img19.png"
 ALT="\begin{table}\begin{center}
\begin{tabularx}{\textwidth}{\vert l \vert p{24ex} \...
...s
you are most interested in.
\\
\hline
\end{tabularx}\end{center}\end{table}"></TD></TR>
</TABLE>
</DIV><P></P>
<BR>

<P>
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/par</FONT></TT><I>?</I> (6)</STRONG></DT>
<DD><I>Parallel port</I>. <TT>
<FONT COLOR="#0000ff">/dev/par0</FONT></TT> is your first
parallel port or LPT1 under DOS.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/lp</FONT></TT><I>?</I> (6)</STRONG></DT>
<DD><I>Line printer</I>. Identical to <TT>
<FONT COLOR="#0000ff">/dev/par</FONT></TT><I>?</I>.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/urandom</FONT></TT></STRONG></DT>
<DD><I>Random</I> number generator. Reading from this device
gives pseudo-random numbers.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/st</FONT></TT><I>?</I> (9)</STRONG></DT>
<DD><I>SCSI tape</I>. SCSI backup tape drive.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/zero</FONT></TT> (1)</STRONG></DT>
<DD>Produces zero bytes, and as many of them as you need. This is useful
if you need to generate a block of zeros for some reason. Use <TT>
<FONT COLOR="#0000ff">dd</FONT></TT> (see Section <A HREF="node21.html#sec:ddzero">18.5.2</A>)
to read a specific number of zeros.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/null</FONT></TT> (1)</STRONG></DT>
<DD><I>Null device</I>. Reads nothing. Anything you write to the device is discarded.
This is very useful for discarding output.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/pd</FONT></TT><I>?</I></STRONG></DT>
<DD><I>Parallel port IDE disk</I>.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/pcd</FONT></TT><I>?</I></STRONG></DT>
<DD><I>Parallel port ATAPI CD-ROM</I>.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/pf</FONT></TT><I>?</I></STRONG></DT>
<DD><I>Parallel port ATAPI disk</I>.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/sr</FONT></TT><I>?</I></STRONG></DT>
<DD><I>SCSI CD-ROM</I>.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/scd</FONT></TT><I>?</I></STRONG></DT>
<DD><I>SCSI CD-ROM</I> (Identical, alternate name).
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/sg</FONT></TT><I>?</I></STRONG></DT>
<DD><I>SCSI generic</I>. This is a general-purpose SCSI command interface for
devices like scanners.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/fb</FONT></TT><I>?</I> (29)</STRONG></DT>
<DD><I>Frame buffer</I>. This represents the kernel's attempt at
a graphics driver.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/cdrom</FONT></TT></STRONG></DT>
<DD>A symlink to
<TT>
<FONT COLOR="#0000ff">/dev/hda</FONT></TT>, <TT>
<FONT COLOR="#0000ff">/dev/hdb</FONT></TT>, or <TT>
<FONT COLOR="#0000ff">/dev/hdc</FONT></TT>. It can also be linked to your SCSI CD-ROM.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/ttyI</FONT></TT><I>?</I></STRONG></DT>
<DD><I>ISDN modems</I>.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/tty</FONT></TT><I>?</I> (4)</STRONG></DT>
<DD><I>Virtual console</I>. This is the terminal device for
the virtual console itself and is numbered <TT>
<FONT COLOR="#0000ff">/dev/tty1</FONT></TT> through <TT>
<FONT COLOR="#0000ff">/dev/tty63</FONT></TT>.
</DD>
<DT><STRONG><TT>
<FONT COLOR="#0000ff">/dev/tty</FONT></TT><I>??</I> (3) and <TT>
<FONT COLOR="#0000ff">/dev/pty</FONT></TT><I>??</I> (2)</STRONG></DT>
<DD>Other
<I>TTY</I> devices used for emulating a terminal. These are
called <I>pseudo-TTY</I>s and are identified by two lowercase
letters and numbers, such as <TT>
<FONT COLOR="#0000ff">ttyq3</FONT></TT>. To nondevelopers,
these are mostly of theoretical interest.
</DD>
</DL>

<P>
The file <TT>
<FONT COLOR="#0000ff">/usr/src/linux/Documentation/devices.txt</FONT></TT> also has this to
say (quoted verbatim):

<P>
<BLOCKQUOTE>
 <FONT SIZE="-1"><B>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Recommended links</B>
</FONT></BLOCKQUOTE>
<P>
<BLOCKQUOTE><FONT SIZE="-1">It is recommended that these links exist on all systems:
</FONT></BLOCKQUOTE>
<P>
<BLOCKQUOTE><IMG
 WIDTH="515" HEIGHT="159" ALIGN="BOTTOM" BORDER="0"
 SRC="img20.png"
 ALT="\begin{tabular}{l \vert l \vert l \vert l}
\texttt{\protect\leavevmode{\color{bl...
...}{sr}}}\emph{?} &amp; hard &amp; Alternate SCSI CD-ROM \\
&amp; &amp; &amp; name \\
\end{tabular}">
<BR>
<FONT SIZE="-1">
<BR>
<BR>
</FONT></BLOCKQUOTE>
<P>
<BLOCKQUOTE><FONT SIZE="-1"><B>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Locally defined links</B>
</FONT></BLOCKQUOTE>
<P>
<BLOCKQUOTE><FONT SIZE="-1">The following links may be established locally to conform to the
configuration of the system.  This is merely a tabulation of existing
practice, and does not constitute a recommendation.  However, if they
exist, they should have the following uses:
</FONT></BLOCKQUOTE>
<P>
<BLOCKQUOTE><IMG
 WIDTH="544" HEIGHT="159" ALIGN="BOTTOM" BORDER="0"
 SRC="img21.png"
 ALT="\begin{tabular}{l \vert l \vert l \vert l}
\texttt{\protect\leavevmode{\color{bl...
...e}{/dev/swap}}} &amp; swap device &amp; symbolic &amp; Current swap device \\
\end{tabular}">
<BR>
</BLOCKQUOTE>
<P>
<BLOCKQUOTE><FONT SIZE="-1"><TT>
<FONT COLOR="#0000ff">/dev/modem</FONT></TT> should not be used for a modem which supports dial-in as
well as dialout, as it tends to cause lock file problems.  If it
exists, <TT>
<FONT COLOR="#0000ff">/dev/modem</FONT></TT> should point to the appropriate primary TTY device
(the use of the alternate callout devices is deprecated).
</FONT></BLOCKQUOTE>
<P>
<BLOCKQUOTE><FONT SIZE="-1">For SCSI devices, <TT>
<FONT COLOR="#0000ff">/dev/tape</FONT></TT> and <TT>
<FONT COLOR="#0000ff">/dev/cdrom</FONT></TT> should point to the
``cooked'' devices (<TT>
<FONT COLOR="#0000ff">/dev/st</FONT></TT><I>*</I> and <TT>
<FONT COLOR="#0000ff">/dev/sr</FONT></TT><I>*</I>, respectively), whereas
<TT>
<FONT COLOR="#0000ff">/dev/cdwriter</FONT></TT> and <TT>
<FONT COLOR="#0000ff">/dev/scanner</FONT></TT> should point to the appropriate generic
SCSI devices (<TT>
<FONT COLOR="#0000ff">/dev/sg</FONT></TT><I>*</I>).
</FONT></BLOCKQUOTE>
<P>
<BLOCKQUOTE><FONT SIZE="-1"><TT>
<FONT COLOR="#0000ff">/dev/mouse</FONT></TT> may point to a primary serial TTY device, a hardware mouse
device, or a socket for a mouse driver program (e.g. <TT>
<FONT COLOR="#0000ff">/dev/gpmdata</FONT></TT>).
<BR>
<BR>
</FONT></BLOCKQUOTE>
<P>
<BLOCKQUOTE><FONT SIZE="-1"><B>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Sockets and pipes</B>
</FONT></BLOCKQUOTE>
<P>
<BLOCKQUOTE><FONT SIZE="-1">Non-transient sockets and named pipes may exist in <TT>
<FONT COLOR="#0000ff">/dev</FONT></TT>.  Common entries are:
</FONT></BLOCKQUOTE>
<P>
<BLOCKQUOTE><IMG
 WIDTH="329" HEIGHT="64" ALIGN="BOTTOM" BORDER="0"
 SRC="img22.png"
 ALT="\begin{tabular}{l \vert l \vert l}
\texttt{\protect\leavevmode{\color{blue}{/dev...
...mode{\color{blue}{/dev/gpmdata}}} &amp; socket &amp; mouse multiplexer \\
\end{tabular}">
<BR>


</BLOCKQUOTE>

<P>

<H1><A NAME="SECTION002150000000000000000">
18.5 <TT>
<FONT COLOR="#0000ff">dd</FONT></TT>, <TT>
<FONT COLOR="#0000ff">tar</FONT></TT>, and Tricks with Block Devices</A>
</H1>

<P>
<TT>
<FONT COLOR="#0000ff">dd</FONT></TT> probably originally stood for <I>disk dump</I>. It is actually just
like <TT>
<FONT COLOR="#0000ff">cat</FONT></TT> except it can read and write in discrete
blocks. It essentially reads and writes between devices while
converting the data in some way. It is generally used in one of these ways:

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<font size="-1"><code>5</code></font><code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>dd&nbsp;if=&#060;in-file&#062;&nbsp;of=&#060;out-file&#062;&nbsp;[bs=&#060;block-size&#062;]&nbsp;\</code><br>
<code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[count=&#060;number-of-blocks&#062;]&nbsp;[seek=&#060;output-offset&#062;]&nbsp;\</code><br>
<code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[skip=&#060;input-offset&#062;]</code><br>
<code>&nbsp;</code><br>
<code>dd&nbsp;if=&#060;in-file&#062;&nbsp;[bs=&#060;block-size&#062;]&nbsp;[count=&#060;number-of-blocks&#062;]&nbsp;\</code><br>
<code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[skip=&#060;input-offset&#062;]&nbsp;&#062;&nbsp;&#060;outfile&#062;</code><br>
<code>&nbsp;</code><br>
<code>dd&nbsp;of=&#060;out-file&#062;&nbsp;[bs=&#060;block-size&#062;]&nbsp;[count=&#060;number-of-blocks&#062;]&nbsp;\</code><br>
<code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[seek=&#060;output-offset&#062;]&nbsp;&#060;&nbsp;&#060;infile&#062;</code><br>
</FONT></TD></TR></TABLE><P>

<P>
To use <TT>
<FONT COLOR="#0000ff">dd</FONT></TT>, you must specify an input file and an output file with the
<TT>
<FONT COLOR="#0000ff">if=</FONT></TT> and <TT>
<FONT COLOR="#0000ff">of=</FONT></TT> options. If the <TT>
<FONT COLOR="#0000ff">of=</FONT></TT> option is omitted,
then <TT>
<FONT COLOR="#0000ff">dd</FONT></TT> writes to stdout. If the <TT>
<FONT COLOR="#0000ff">if=</FONT></TT> option is omitted,
then <TT>
<FONT COLOR="#0000ff">dd</FONT></TT> reads from stdin. <FONT COLOR="#ffa500">[If you are confused, remember that
<TT>
<FONT COLOR="#0000ff">dd</FONT></TT> thinks of <I>in</I> and <I>out</I> with respect to itself.]</FONT>
<P>
Note that <TT>
<FONT COLOR="#0000ff">dd</FONT></TT> is an unforgiving and destructive command
that should be used with caution.

<P>

<H2><A NAME="SECTION002151000000000000000">
18.5.1 Creating boot disks from boot images</A>
</H2>

<P>
To create a new RedHat boot floppy, find the <TT>
<FONT COLOR="#0000ff">boot.img</FONT></TT> file on <TT>
<FONT COLOR="#0000ff">ftp.redhat.com</FONT></TT>,
and with a new floppy, run:

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>dd&nbsp;if=boot.img&nbsp;of=/dev/fd0</code><br>
</FONT></TD></TR></TABLE><P>
This command writes the raw disk image directly to the floppy disk. All distributions will
have similar disk images for creating installation floppies (and sometimes rescue floppies).

<P>

<H2><A NAME="SECTION002152000000000000000">
18.5.2 Erasing disks</A>
</H2>

<P>
<A NAME="sec:ddzero"></A>
<P>
If you have ever tried to repartition a L<SMALL>INUX</SMALL> disk back into a
DOS/Windows disk, you will
know that DOS/Windows <TT>
<FONT COLOR="#0000ff">FDISK</FONT></TT> has bugs in it that prevent it from recreating the
partition table. A quick

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>dd&nbsp;if=/dev/zero&nbsp;of=/dev/hda&nbsp;bs=1024&nbsp;count=10240</code><br>
</FONT></TD></TR></TABLE><P>
will write zeros to the first 10 megabytes of your first IDE drive.
This will wipe out the partition table as well as any
file system information and give you a ``brand new'' disk.

<P>
To zero a floppy disk is just as easy:

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>dd&nbsp;if=/dev/zero&nbsp;of=/dev/fd0&nbsp;bs=1024&nbsp;count=1440</code><br>
</FONT></TD></TR></TABLE><P>

<P>
Even writing zeros to a floppy may not be sufficient. Specialized equipment
can probably still read magnetic media after it has been erased several
times. If, however, you write random bits to the floppy, it becomes
completely impossible to determine what was on it:

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>mknod&nbsp;/dev/urandom&nbsp;c&nbsp;1&nbsp;9</code><br>
<code>for&nbsp;i&nbsp;in&nbsp;1&nbsp;2&nbsp;3&nbsp;4&nbsp;&#059;&nbsp;do</code><br>
<code>&nbsp;&nbsp;&nbsp;&nbsp;dd&nbsp;if=/dev/urandom&nbsp;of=/dev/fd0&nbsp;bs=1024&nbsp;count=1440</code><br>
<code>done</code><br>
</FONT></TD></TR></TABLE><P>

<P>

<H2><A NAME="SECTION002153000000000000000">
18.5.3 Identifying data on raw disks</A>
</H2>

<P>
Here is a nice trick to find out something about a hard drive:

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>dd&nbsp;if=/dev/hda1&nbsp;count=1&nbsp;bs=512&nbsp;|&nbsp;file&nbsp;-</code><br>
</FONT></TD></TR></TABLE><P>
gives <TT>
<FONT COLOR="#0000ff">x86 boot sector</FONT></TT>.

<P>
To discover what a floppy disk is, try

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>dd&nbsp;if=/dev/fd0&nbsp;count=1&nbsp;bs=512&nbsp;|&nbsp;file&nbsp;-</code><br>
</FONT></TD></TR></TABLE><P>
which gives <TT>
<FONT COLOR="#0000ff">x86 boot sector, system )k?/bIHC, FAT (12 bit)</FONT></TT>
for DOS floppies.

<P>

<H2><A NAME="SECTION002154000000000000000">
18.5.4 Duplicating a disk</A>
</H2>

<P>
If you have two IDE drives that are of identical size, and provided that
you are sure they contain no bad sectors and <I>provided
neither are mounted</I>, you can run

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>dd&nbsp;if=/dev/hdc&nbsp;of=/dev/hdd</code><br>
</FONT></TD></TR></TABLE><P>
to copy the entire disk and avoid having to install an operating
system from scratch. It doesn't matter what is on the original
(Windows, L<SMALL>INUX</SMALL>, or whatever) since each sector is identically
duplicated; the new system will work perfectly.

<P>
(If they are not the same size, you will have to use
<TT>
<FONT COLOR="#0000ff">tar</FONT></TT> or <TT>
<FONT COLOR="#0000ff">mirrordir</FONT></TT> to replicate the file system exactly.)

<P>

<H2><A NAME="SECTION002155000000000000000">
18.5.5 Backing up to floppies</A>
</H2>

<P>
You can use <TT>
<FONT COLOR="#0000ff">tar</FONT></TT> to back up to <I>any</I> device.
Consider periodic backups to an ordinary IDE drive instead of a
tape. Here we back up to the secondary slave:

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>tar&nbsp;-cvzf&nbsp;/dev/hdd&nbsp;/bin&nbsp;/boot&nbsp;/dev&nbsp;/etc&nbsp;/home&nbsp;/lib&nbsp;/sbin&nbsp;/usr&nbsp;/var</code><br>
</FONT></TD></TR></TABLE><P>

<P>
<TT>
<FONT COLOR="#0000ff">tar</FONT></TT> can also back up across multiple floppy disks:

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>tar&nbsp;-cvMf&nbsp;/dev/fd0&nbsp;/home/simon</code><br>
</FONT></TD></TR></TABLE><P>

<P>

<H2><A NAME="SECTION002156000000000000000">
18.5.6 Tape backups</A>
</H2>

<P>
<A NAME="page:tapebackups"></A><TT>
<FONT COLOR="#0000ff">tar</FONT></TT> traditionally backs up onto tape drives. The commands

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>mt&nbsp;-f&nbsp;/dev/st0&nbsp;rewind</code><br>
<code>tar&nbsp;-cvf&nbsp;/dev/st0&nbsp;/home</code><br>
</FONT></TD></TR></TABLE><P>
rewind <TT>
<FONT COLOR="#0000ff">s</FONT></TT>csi <TT>
<FONT COLOR="#0000ff">t</FONT></TT>ape <TT>
<FONT COLOR="#0000ff">0</FONT></TT> and archive the
<TT>
<FONT COLOR="#0000ff">/home</FONT></TT> directory onto it. You should not try to use
compression with tape drives because they are error prone, and a single
error could make the entire archive unrecoverable. The <TT>
<FONT COLOR="#0000ff">mt</FONT></TT> command stands
for <TT>
<FONT COLOR="#0000ff">m</FONT></TT>agnetic <TT>
<FONT COLOR="#0000ff">t</FONT></TT>ape and controls generic SCSI tape
devices. See also <TT>
<FONT COLOR="#0000ff">mt</FONT></TT>(1).

<P>

<H2><A NAME="SECTION002157000000000000000">
18.5.7 Hiding program output, creating blocks of zeros</A>
</H2>

<P>
If you don't want to see any program output,
just append <TT>
<FONT COLOR="#0000ff">&gt; /dev/null</FONT></TT> to the command. For example,
we aren't often interested in the output of
<TT>
<FONT COLOR="#0000ff">make</FONT></TT>. <FONT COLOR="#ffa500">[<TT>
<FONT COLOR="#0000ff">make</FONT></TT> is discussed later.]</FONT>Here we absorb everything save for error messages.

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>make&nbsp;&#062;&nbsp;/dev/null</code><br>
</FONT></TD></TR></TABLE><P>
Then, of course, we can absorb all output <I>including</I> error messages
with either

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>make&nbsp;&#062;&#038;&nbsp;/dev/null</code><br>
</FONT></TD></TR></TABLE><P>
or

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>make&nbsp;&#062;&nbsp;/dev/null&nbsp;2&#062;&#038;1</code><br>
</FONT></TD></TR></TABLE><P>
The device <TT>
<FONT COLOR="#0000ff">/dev/null</FONT></TT> finds
innumerable uses in shell scripting to suppress the output of a
command or to feed a command dummy (empty) input.
<TT>
<FONT COLOR="#0000ff">/dev/null</FONT></TT> is a <I>safe</I> file from a security point
of view. It is often used when a file is required for some
feature in a configuration script, and you would like the
particular feature disabled. For instance, specifying the users
shell to <TT>
<FONT COLOR="#0000ff">/dev/null</FONT></TT> inside the password file will
<I>certainly</I> prevent insecure use of a shell, and is an explicit
way of saying that that account does <I>not</I> allow shell
logins.

<P>
You can also use <TT>
<FONT COLOR="#0000ff">/dev/null</FONT></TT> to create a file containing nothing:

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>cat&nbsp;/dev/null&nbsp;&#062;&nbsp;myfile</code><br>
</FONT></TD></TR></TABLE><P>
or alternatively, to create a file containing only zeros. Try

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>dd&nbsp;if=/dev/zero&nbsp;bs=1024&nbsp;count=&#060;number-of-kilobytes&#062;&nbsp;&#062;&nbsp;myfile</code><br>
</FONT></TD></TR></TABLE><P>

<P>

<H1><A NAME="SECTION002160000000000000000">
18.6 Creating Devices with <TT>
<FONT COLOR="#0000ff">mknod</FONT></TT> and <TT>
<FONT COLOR="#0000ff">/dev/MAKEDEV</FONT></TT></A>
</H1>

<P>
Although all devices are listed in the <TT>
<FONT COLOR="#0000ff">/dev</FONT></TT> directory,
you can create a device anywhere in the file system by using the
<TT>
<FONT COLOR="#0000ff">mknod</FONT></TT> command:

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>mknod&nbsp;[-m&nbsp;&#060;mode&#062;]&nbsp;&#060;file-name&#062;&nbsp;[b|c]&nbsp;&#060;major-number&#062;&nbsp;&#060;minor-number&#062;</code><br>
</FONT></TD></TR></TABLE><P>

<P>
The letters <TT>
<FONT COLOR="#0000ff">b</FONT></TT> and <TT>
<FONT COLOR="#0000ff">c</FONT></TT> are for creating a block
or character device, respectively.

<P>
To demonstrate, try

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>mknod&nbsp;-m&nbsp;0600&nbsp;~/my-floppy&nbsp;b&nbsp;2&nbsp;0</code><br>
<code>ls&nbsp;-al&nbsp;/dev/fd0&nbsp;~/my-floppy</code><br>
</FONT></TD></TR></TABLE><P>
<TT>
<FONT COLOR="#0000ff">my-floppy</FONT></TT> can be used just like <TT>
<FONT COLOR="#0000ff">/dev/fd0</FONT></TT>

<P>
Note carefully the <I>mode</I> (i.e., the permissions) of <TT>
<FONT COLOR="#0000ff">/dev/fd0</FONT></TT>.
<TT>
<FONT COLOR="#0000ff">/dev/fd0</FONT></TT> should be readable and writable only to <TT>
<FONT COLOR="#0000ff">root</FONT></TT> and
to users belonging to the <TT>
<FONT COLOR="#0000ff">floppy</FONT></TT> group, since we
obviously don't want an arbitrary user to be able to log in
(remotely) and overwrite a floppy disk.

<P>
In fact, this is the reason for having devices represented as
files in the first place. U<SMALL>NIX</SMALL> files naturally support group
access control, and therefore so do devices.

<P>
To create devices that are missing from your <TT>
<FONT COLOR="#0000ff">/dev</FONT></TT>
directory (some esoteric devices will not be present by
default), simply look up the device's major and minor number in
<TT>
<FONT COLOR="#0000ff">/usr/src/linux/Documentation/devices.txt</FONT></TT> and use the
<TT>
<FONT COLOR="#0000ff">mknod</FONT></TT> command. This procedure is, however, somewhat tedious, and
the script <TT>
<FONT COLOR="#0000ff">/dev/MAKEDEV</FONT></TT> is usually available for convenience.
<I>You must be in the <TT>
<FONT COLOR="#0000ff">/dev</FONT></TT> directory before you run this
script.</I>

<P>
Typical usage of <TT>
<FONT COLOR="#0000ff">MAKEDEV</FONT></TT> is

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>cd&nbsp;/dev</code><br>
<code>./MAKEDEV&nbsp;-v&nbsp;fd0</code><br>
<code>./MAKEDEV&nbsp;-v&nbsp;fd1</code><br>
</FONT></TD></TR></TABLE><P>
to create a complete set of floppy disk devices.

<P>
The <TT>
<FONT COLOR="#0000ff">man</FONT></TT> page for <TT>
<FONT COLOR="#0000ff">MAKEDEV</FONT></TT> contains more
details. In particular, it states:

<P>

<BLOCKQUOTE><FONT SIZE="-1">Note that programs giving the error ``ENOENT: No such file
       or  directory''  normally  means  that  the device file is
       missing, whereas ``ENODEV: No such device'' normally means
       the  kernel does not have the driver configured or loaded.
</FONT></BLOCKQUOTE>

<P>
<HR>
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