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>How does kerneld know what module
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CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="CONFIGURATION"
>How does kerneld know what module
to load?</A
></H1
><P
>Although kerneld comes with builtin knowledge about the
most common types of modules, there are situations where kerneld
will not know how to handle a request from the kernel. This is
the case with things like CD-ROM drivers or network drivers,
where there are more than one possible module that can be
loaded. </P
><P
>The requests that the kerneld daemon gets from the kernel
is for one of the following items: </P
><P
></P
><UL
><LI
><P
>a block-device driver </P
></LI
><LI
><P
>a character-device driver </P
></LI
><LI
><P
>a binary format </P
></LI
><LI
><P
>a tty line discipline </P
></LI
><LI
><P
>a filesystem </P
></LI
><LI
><P
>a network device </P
></LI
><LI
><P
>a network service (e.g. rarp) </P
></LI
><LI
><P
>a network protocol (e.g. IPX)
</P
></LI
></UL
><P
>The kerneld determines what module should be loaded by
scanning the configuration file
<TT
CLASS="FILENAME"
>/etc/conf.modules</TT
><A
NAME="AEN192"
HREF="#FTN.AEN192"
>[1]</A
>. There are
two kinds of entries in this file: Paths where the module-files
are located, and aliases assigning the module to be loaded for a
given service. If you don't have this file already, you could
create it by running
</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
> /sbin/modprobe -c | grep -v '^path' /etc/conf.modules</PRE
></TD
></TR
></TABLE
><P
>If you want to add yet another path directive to the
default paths, you <I
CLASS="EMPHASIS"
>must include all the default paths
as well</I
>, since a path directive in
<TT
CLASS="FILENAME"
>/etc/conf.modules</TT
> will
<I
CLASS="EMPHASIS"
>replace</I
>all the ones that modprobe knows by
default! </P
><P
>Normally you don't want to add any paths by your own,
since the built-in set should take care of all normal setups
(and then some...), I promise! </P
><P
>On the other hand, if you just want to add an alias or an
option directive, your new entries in
<TT
CLASS="FILENAME"
>/etc/conf.modules</TT
> will be
<I
CLASS="EMPHASIS"
>added</I
> to the ones that modprobe already
knows. If you should <I
CLASS="EMPHASIS"
>redefine</I
> an alias or
an option, your new entries in
<TT
CLASS="FILENAME"
>/etc/conf.modules</TT
> will override the
built-in ones.</P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="BLOCKDEV"
>Block devices</A
></H2
><P
>If you run <B
CLASS="COMMAND"
>/sbin/modprobe -c</B
>, you
will get a listing of the modules that kerneld knows about, and
what requests they correspond to. For instance, the request that
ends up loading the floppy driver is for the block-device that
has major number 2: </P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
> osiris:~ $ /sbin/modprobe -c | grep floppy
alias block-major-2 floppy</PRE
></TD
></TR
></TABLE
><P
>Why <TT
CLASS="FILENAME"
>block-major-2</TT
> ? Because the
floppy devices <TT
CLASS="FILENAME"
>/dev/fd*</TT
> use major device 2
and are block devices:
</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
> osiris:~ $ ls -l /dev/fd0 /dev/fd1
brw-rw-rw- 1 root root 2, 0 Mar 3 1995 /dev/fd0
brw-r--r-- 1 root root 2, 1 Mar 3 1995 /dev/fd1</PRE
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="CHARDEV"
>Character devices</A
></H2
><P
>Character devices are dealt with in a similar
way. E.g. the ftape floppy tape driver sits on major-device
27: </P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
> osiris:~ $ ls -lL /dev/ftape
crw-rw---- 1 root disk 27, 0 Jul 18 1994 /dev/ftape</PRE
></TD
></TR
></TABLE
><P
>However, kerneld does not by default know about the
ftape driver - it is not listed in the output from
<B
CLASS="COMMAND"
>/sbin/modprobe -c</B
>. So to setup kerneld to
load the ftape driver, I must add a line to the kerneld
configuration file, <TT
CLASS="FILENAME"
>/etc/conf.modules</TT
>:
</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
> alias char-major-27 ftape</PRE
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="ETH0"
>Network devices</A
></H2
><P
>You can also use the device name instead of the
<TT
CLASS="LITERAL"
>char-major-xxx</TT
> or
<TT
CLASS="LITERAL"
>block-major-yyy</TT
> setup. This is especially
useful for network drivers. For example, a driver for an
ne2000 netcard acting as <TT
CLASS="FILENAME"
>eth0</TT
> would be
loaded with </P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
> alias eth0 ne</PRE
></TD
></TR
></TABLE
><P
>If you need to pass some options to the driver, for
example to tell the module about what IRQ the netcard is
using, you must add an <SPAN
CLASS="QUOTE"
>"options"</SPAN
> line: </P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
> options ne irq=5</PRE
></TD
></TR
></TABLE
><P
>This will cause kerneld to load the NE2000 driver with
the command </P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
> /sbin/modprobe ne irq=5</PRE
></TD
></TR
></TABLE
><P
>Of course, the actual options available are specific to
the module you are loading. </P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="BINFMT"
>Binary formats</A
></H2
><P
>Binary formats are handled in a similar way. Whenever
you try to run a program that the kernel does not know how to
load, kerneld gets a request for
<TT
CLASS="LITERAL"
>binfmt-</TT
><TT
CLASS="VARNAME"
>xxx</TT
>, where
<TT
CLASS="VARNAME"
>xxx</TT
> is a number determined from the first
few bytes of the executable. So, the kerneld configuration to
support loading the binfmt_aout module for ZMAGIC (a.out)
executables is
</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
> alias binfmt-267 binfmt_aout</PRE
></TD
></TR
></TABLE
><P
>Since the magic number for ZMAGIC files is 267, if you
check <TT
CLASS="FILENAME"
>/etc/magic</TT
>, you will see the number
0413; keep in mind that <TT
CLASS="FILENAME"
>/etc/magic</TT
> uses
octal numbers where kerneld uses decimal, and octal 413 =
decimal 267. There are actually three slightly different
variants of a.out executables (NMAGIC, QMAGIC and ZMAGIC), so
for full support of the binfmt_aout module we need
</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
> alias binfmt-264 binfmt_aout # pure executable (NMAGIC)
alias binfmt-267 binfmt_aout # demand-paged executable (ZMAGIC)
alias binfmt-204 binfmt_aout # demand-paged executable (QMAGIC)</PRE
></TD
></TR
></TABLE
><P
>a.out, Java and iBCS binary formats are recognized
automatically by kerneld, without any configuration. </P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="LDISC"
>Line disciplines (slip, cslip and ppp)</A
></H2
><P
>Line disciplines are requested with
<TT
CLASS="LITERAL"
>tty-ldisc-</TT
><TT
CLASS="VARNAME"
>x</TT
>, with
<TT
CLASS="VARNAME"
>x</TT
>
being usually 1 (for SLIP) or 3 (for PPP). Both of these are
known by kerneld automatically. </P
><P
>Speaking of ppp, if you want kerneld to load the
bsd_comp data compression module for ppp, then you must add
the following two lines to your
<TT
CLASS="FILENAME"
>/etc/conf.modules</TT
>:</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
> alias tty-ldisc-3 bsd_comp
alias ppp0 bsd_comp</PRE
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="NET-PF"
>Network protocol families (IPX,
AppleTalk, AX.25)</A
></H2
><P
>Some network protocols can be loaded as modules as
well. The kernel asks kerneld for a protocol family (e.g. IPX)
with a request for
<TT
CLASS="LITERAL"
>net-pf-</TT
><TT
CLASS="VARNAME"
>X</TT
> where
<TT
CLASS="VARNAME"
>X</TT
> is a number indicating what family is
wanted. E.g. <TT
CLASS="LITERAL"
>net-pf-3</TT
> is AX.25,
<TT
CLASS="LITERAL"
>net-pf-4</TT
> is IPX and
<TT
CLASS="LITERAL"
>net-pf-5</TT
> is AppleTalk; These numbers are
determined by the AF_AX25, AF_IPX etc. definitions in the
linux source file <TT
CLASS="FILENAME"
>include/linux/socket.h</TT
>.
So to autoload the IPX module, you would need an entry like
this in <TT
CLASS="FILENAME"
>/etc/conf.modules</TT
>:</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
> alias net-pf-4 ipx</PRE
></TD
></TR
></TABLE
><P
>See <A
HREF="commonproblems.html"
>Common Problems</A
> for information
about how you can avoid some annoying boot-time messages
related to undefined protocol families. </P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="FS"
>File systems</A
></H2
><P
>kerneld requests for filesystems are simply the name of
the filesystem type. A common use of this would be to load the
isofs module for CD-ROM filesystems, i.e. filesystems of type
iso9660: </P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
> alias iso9660 isofs</PRE
></TD
></TR
></TABLE
></DIV
></DIV
><H3
CLASS="FOOTNOTES"
>Notes</H3
><TABLE
BORDER="0"
CLASS="FOOTNOTES"
WIDTH="100%"
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN192"
HREF="configuration.html#AEN192"
>[1]</A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
>Some
distributions call this file
<TT
CLASS="FILENAME"
>modules.conf</TT
></P
></TD
></TR
></TABLE
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