Difference between revisions of "EXTLINUX"

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==EXTLINUX - SYSLINUX for ext2/ext3 filesystems==
+
EXTLINUX is a Syslinux variant which boots from a Linux filesystem.
EXTLINUX is a new syslinux derivative, which boots from a Linux
+
 
ext2/ext3 filesystem.
+
EXTLINUX [[Filesystem|supports]]:<br />
 +
{{V|3.00+}}ext2/3,<br />
 +
{{V|4.00+}}FAT12/16/32, ext2/3/4, Btrfs,<br />
 +
{{V|4.06+}}FAT12/16/32, NTFS, ext2/3/4, Btrfs,<br />
 +
{{V|5.01+}}FAT12/16/32, NTFS, ext2/3/4, Btrfs, XFS,<br />
 +
{{V|6.03+}}FAT12/16/32, NTFS, ext2/3/4, Btrfs, XFS, UFS/FFS,<br />
 +
 
  
 
It works the same way as SYSLINUX, with a few slight modifications.
 
It works the same way as SYSLINUX, with a few slight modifications.
  
1. The installer is run on a *mounted* filesystem.  Run the extlinux
 
installer on the directory in which you want extlinux installed:
 
  
        extlinux /boot
+
1. The [[install]]er runs on a *'''mounted'''* filesystem.
 +
Run the extlinux installer on the directory in which you want EXTLINUX installed:
 +
 
 +
extlinux --install /boot  
 +
 
 +
Specify <tt>--install (-i)</tt> to install for the first time, or <tt>--update (-U)</tt> to upgrade a previous installation.
 +
 
 +
NOTE: This does not have to be the root directory of a filesystem.
 +
If "<tt>/boot</tt>" is a mount point of a supported filesystem, then you can do:
 +
 
 +
mkdir -p /boot/extlinux
 +
extlinux --install /boot/extlinux
 +
 
 +
... to create a subdirectory and install EXTLINUX in it.
 +
 
 +
 
 +
2. The [[config]]uration file is called "<tt>extlinux.conf</tt>", and is expected
 +
to be found in the same directory as EXTLINUX is installed in.
 +
 
 +
Since v.4.02, <tt>syslinux.cfg</tt> and {{nowrap|<tt>[/boot/]syslinux/</tt>}} are generic terms and also valid for EXTLINUX.
 +
<tt>extlinux.conf</tt> and {{nowrap|<tt>[/boot/]extlinux/</tt>}} take precedence for EXTLINUX if they are present.
 +
 
 +
 
 +
3. Pathnames can be absolute or relative;
 +
if absolute (with a leading slash),
 +
they are relative to the root of the filesystem on which EXTLINUX is installed (<tt>/boot</tt> in the example above);
 +
if relative,
 +
they are relative to the Current Working Directory -
 +
initially the EXTLINUX directory (where <tt>extlinux.conf</tt> - or the alternative <tt>syslinux.cfg</tt> - is located).
 +
<!-- See [[Configuration_location_and_name]] -->
 +
 
 +
EXTLINUX supports subdirectories, but the total path length is limited to 255 characters.
 +
 
 +
 
 +
4. EXTLINUX supports symbolic links.
 +
However, extremely long symbolic links might hit the pathname limit.
 +
Also, please note that absolute symbolic links are interpreted from the root {{nowrap|*<u>of the filesystem</u>*}},
 +
which might be different from how the running system would interpret it (e.g. in the case of a separate <tt>/boot</tt> partition.)
 +
Therefore, use relative symbolic links if at all possible.
 +
 
 +
 
 +
5. EXTLINUX has "boot-once" support.
 +
The boot-once information is stored in an on-disk datastructure,
 +
part of ldlinux.sys,
 +
called the "''Auxillary Data Vector''".
 +
The Auxilliary Data Vector is also available to c32 modules that want to store small amounts of information.
 +
 
 +
To set the boot-once information:
  
NOTE: this doesn't have to be the root directory of a filesystem.
+
extlinux --once 'command' /boot/extlinux
If /boot is a filesystem, you can do:
+
  
        mkdir -p /boot/extlinux
+
where "''command''" is any command you could enter at the Syslinux command line, preferably a label.
        extlinux /boot/extlinux
+
The boot-once information will be executed on the next boot and then erased.
  
... to create a subdirectory and install extlinux in it.
+
To clear the boot-once information:
  
 +
extlinux --clear-once /boot/extlinux
  
2. The configuration file is called "extlinux.conf", and is expected
+
If EXTLINUX is used on a RAID-1, this is recommended, since under certain circumstances a RAID-1 rebuild can "resurrect" the boot-once information otherwise.
to be found in the same directory as extlinux is installed in.
+
  
 +
To clear the entire Auxillary Data Vector:
  
3. Pathnames can be absolute or relative; if absolute (with a leading
+
extlinux --reset-adv /boot/extlinux
slash), they are relative to the root of the filesystem on which
+
extlinux is installed (/boot in the example above), if relative,
+
they are relative to the extlinux directory.
+
  
extlinux supports subdirectories, but the total path length is
+
This will erase all data stored in the ADV, including boot-once.
limited to 255 characters.
+
  
 +
The <tt>--once</tt>, <tt>--clear-once</tt>, and <tt>--reset-adv</tt> commands can be combined with {{nowrap|<tt>--install</tt>}} or {{nowrap|<tt>--update</tt>}}, if desired.
 +
The ADV is preserved across updates, unless {{nowrap|<tt>--reset-adv</tt>}} is specified.
  
4. EXTLINUX now supports symbolic links.  However, extremely long
 
symbolic links might hit the pathname limit.  Also, please note
 
that absolute symbolic links are interpreted from the root *of the
 
filesystem*, which might be different from now the running system
 
would interpret it (e.g. in the case of a separate /boot
 
partition.)  Therefore, use relative symbolic links if at all
 
possible.
 
  
 +
Note that EXTLINUX installs in the filesystem partition like a well-behaved bootloader :).
 +
Thus, it needs a master boot record in the partition table;
 +
the [[Mbr|mbr.bin]] shipped with SYSLINUX should work well.
 +
To install it:
  
Note that EXTLINUX installs in the filesystem partition like a
+
  cat mbr.bin > /dev/XXX
well-behaved bootloader :) Thus, it needs a master boot record in the
+
partition table; the mbr.bin shipped with SYSLINUX should work well.
+
To install it just do:
+
  
        cat mbr.bin > /dev/XXX
+
... where ''/dev/XXX'' is the appropriate master device, e.g. /dev/hda,
 +
and make sure the correct partition is set as "active".
  
... where /dev/XXX is the appropriate master device, e.g. /dev/hda,
 
and make sure the correct partition in set active.
 
  
 +
If you have multiple disks in a software RAID configuration,
 +
the preferred way to boot is:
  
If you have multiple disks in a software RAID configuration, the
+
* Create a separate RAID-1 partition for /boot.
preferred way to boot is:
+
: Note that the Linux RAID-1 driver can span as many disks as you wish.
  
* Create a separate RAID-1 partition for /boot.  Note that the Linux
+
* Install the MBR on *<u>each disk</u>*, and mark the RAID-1 partition as "active".
RAID-1 driver can span as many disks as you wish.
+
  
* Install the MBR on *each disk*, and mark the RAID-1 partition
+
* Run {{nowrap|"<code>extlinux --raid --install /boot</code>"}} to install EXTLINUX.
active.
+
:  This will install it on all the drives in the RAID-1 set, which means you can boot any combination of drives in any order.
  
* Run "extlinux /boot" to install extlinux.  This will install it on
 
all the drives in the RAID-1 set, which means you can boot any
 
combination of drives in any order.
 
  
  
 +
It is not required to re-run the extlinux installer after installing new kernels.
 +
If you are using ext3 journalling, however, it might be desirable to do so, since running the extlinux installer will flush the log.
 +
Otherwise a dirty shutdown could cause some of the new kernel image to still be in the log.
 +
This is a general problem for boot loaders on journalling filesystems; it is not specific to EXTLINUX.
 +
The "sync" command does not flush the log on the ext3 filesystem.
  
It is not required to re-run the extlinux installer after installing
 
new kernels.  If you are using ext3 journalling, however, it might be
 
desirable to do so, since running the extlinux installer will flush
 
the log.  Otherwise a dirty shutdown could cause some of the new
 
kernel image to still be in the log.  This is a general problem for
 
boot loaders on journalling filesystems; it is not specific to
 
extlinux.  The "sync" command does not flush the log on the ext3
 
filesystem.
 
  
 +
The Syslinux Project boot loaders support chain loading other operating systems via a separate module, [[Comboot/chain.c32|chain.c32]].
 +
To use it, specify a LABEL in the configuration file with KERNEL chain.c32 and APPEND [hd|fd]<number> [<partition>].
  
The SYSLINUX series boot loaders support chain loading other operating
 
systems via a separate module, chain.c32 (located in
 
com32/modules/chain.c32).  To use it, specify a LABEL in the
 
configuration file with KERNEL chain.c32 and
 
APPEND [hd|fd]<number> [<partition>]
 
  
 
For example:
 
For example:
 +
<pre>
 
  # Windows CE/ME/NT, a very dense operating system.
 
  # Windows CE/ME/NT, a very dense operating system.
 
  # Second partition (2) on the first hard disk (hd0);
 
  # Second partition (2) on the first hard disk (hd0);
 
  # Linux would *typically* call this /dev/hda2 or /dev/sda2.
 
  # Linux would *typically* call this /dev/hda2 or /dev/sda2.
 
  LABEL cement
 
  LABEL cement
        KERNEL chain.c32
+
  KERNEL chain.c32
        APPEND hd0 2
+
  APPEND hd0 2
 +
</pre>
  
See also README.menu.
+
See also [[Comboot/menu.c32]].

Latest revision as of 21:08, 31 March 2017

EXTLINUX is a Syslinux variant which boots from a Linux filesystem.

EXTLINUX supports:
[3.00+] ext2/3,
[4.00+] FAT12/16/32, ext2/3/4, Btrfs,
[4.06+] FAT12/16/32, NTFS, ext2/3/4, Btrfs,
[5.01+] FAT12/16/32, NTFS, ext2/3/4, Btrfs, XFS,
[6.03+] FAT12/16/32, NTFS, ext2/3/4, Btrfs, XFS, UFS/FFS,


It works the same way as SYSLINUX, with a few slight modifications.


1. The installer runs on a *mounted* filesystem. Run the extlinux installer on the directory in which you want EXTLINUX installed:

extlinux --install /boot 

Specify --install (-i) to install for the first time, or --update (-U) to upgrade a previous installation.

NOTE: This does not have to be the root directory of a filesystem. If "/boot" is a mount point of a supported filesystem, then you can do:

mkdir -p /boot/extlinux
extlinux --install /boot/extlinux

... to create a subdirectory and install EXTLINUX in it.


2. The configuration file is called "extlinux.conf", and is expected to be found in the same directory as EXTLINUX is installed in.

Since v.4.02, syslinux.cfg and [/boot/]syslinux/ are generic terms and also valid for EXTLINUX. extlinux.conf and [/boot/]extlinux/ take precedence for EXTLINUX if they are present.


3. Pathnames can be absolute or relative; if absolute (with a leading slash), they are relative to the root of the filesystem on which EXTLINUX is installed (/boot in the example above); if relative, they are relative to the Current Working Directory - initially the EXTLINUX directory (where extlinux.conf - or the alternative syslinux.cfg - is located).

EXTLINUX supports subdirectories, but the total path length is limited to 255 characters.


4. EXTLINUX supports symbolic links. However, extremely long symbolic links might hit the pathname limit. Also, please note that absolute symbolic links are interpreted from the root *of the filesystem*, which might be different from how the running system would interpret it (e.g. in the case of a separate /boot partition.) Therefore, use relative symbolic links if at all possible.


5. EXTLINUX has "boot-once" support. The boot-once information is stored in an on-disk datastructure, part of ldlinux.sys, called the "Auxillary Data Vector". The Auxilliary Data Vector is also available to c32 modules that want to store small amounts of information.

To set the boot-once information:

extlinux --once 'command' /boot/extlinux

where "command" is any command you could enter at the Syslinux command line, preferably a label. The boot-once information will be executed on the next boot and then erased.

To clear the boot-once information:

extlinux --clear-once /boot/extlinux

If EXTLINUX is used on a RAID-1, this is recommended, since under certain circumstances a RAID-1 rebuild can "resurrect" the boot-once information otherwise.

To clear the entire Auxillary Data Vector:

extlinux --reset-adv /boot/extlinux

This will erase all data stored in the ADV, including boot-once.

The --once, --clear-once, and --reset-adv commands can be combined with --install or --update, if desired. The ADV is preserved across updates, unless --reset-adv is specified.


Note that EXTLINUX installs in the filesystem partition like a well-behaved bootloader :). Thus, it needs a master boot record in the partition table; the mbr.bin shipped with SYSLINUX should work well. To install it:

cat mbr.bin > /dev/XXX

... where /dev/XXX is the appropriate master device, e.g. /dev/hda, and make sure the correct partition is set as "active".


If you have multiple disks in a software RAID configuration, the preferred way to boot is:

  • Create a separate RAID-1 partition for /boot.
Note that the Linux RAID-1 driver can span as many disks as you wish.
  • Install the MBR on *each disk*, and mark the RAID-1 partition as "active".
  • Run "extlinux --raid --install /boot" to install EXTLINUX.
This will install it on all the drives in the RAID-1 set, which means you can boot any combination of drives in any order.


It is not required to re-run the extlinux installer after installing new kernels. If you are using ext3 journalling, however, it might be desirable to do so, since running the extlinux installer will flush the log. Otherwise a dirty shutdown could cause some of the new kernel image to still be in the log. This is a general problem for boot loaders on journalling filesystems; it is not specific to EXTLINUX. The "sync" command does not flush the log on the ext3 filesystem.


The Syslinux Project boot loaders support chain loading other operating systems via a separate module, chain.c32. To use it, specify a LABEL in the configuration file with KERNEL chain.c32 and APPEND [hd|fd]<number> [<partition>].


For example:

 # Windows CE/ME/NT, a very dense operating system.
 # Second partition (2) on the first hard disk (hd0);
 # Linux would *typically* call this /dev/hda2 or /dev/sda2.
 LABEL cement
  KERNEL chain.c32
  APPEND hd0 2

See also Comboot/menu.c32.