EXTLINUX

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EXTLINUX - SYSLINUX for ext2/ext3/ext4 and btrfs filesystems

EXTLINUX is a new syslinux derivative, which boots from a Linux ext2/ext3/ext4 or btrfs filesystem. Support for ext4 and btrfs was added in version 4 of extlinux.

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

NOTE: this doesn't have to be the root directory of a filesystem. If /boot is a filesystem, 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 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 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 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.


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 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 in set 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

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 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:

# 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 README.menu.

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