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Booting Linux With the New EXTLINUX - page 2

Boot disks with SYSLINUX and ISOLINUX

  • August 10, 2010
  • By Juliet Kemp

EXTLINUX as a Linux bootloader

The recently-added SYSLINUX derivative EXTLINUX allows booting from Linux ext2/ext3 filesystems, and also, since the 4.00 release, from Btrfs and ext4 filesystems. It works much the same way as SYSLINUX, with the exception that it is run on a mounted filesystem, rather than on a device.

extlinux --install /boot/isolinux
The config file is extlinux.conf and should go in the same directory in which EXTLINUX was installed. As with ISOLINUX, the configuration options and syntax are the same as for syslinux.cfg.

You'll also need a master boot record, since EXTLINUX installs itself (as it should!) in the filesystem partition. The wiki page suggests using the mbr.bin shipped with SYSLINUX and piping that into the correct device:
cat mbr.bin > /dev/hda
You'll need to check before booting that the partition containing EXTLINUX is active. It's also possible to set EXTLINUX up on a software RAID system; the details are explained on the wiki.

A quick note in case you (like me!) weren't familiar with the Btrfs filesystem: it's a newly-developed copy-on-write filesystem for Linux. It handles online growing/shrinking, snapshots, and subvolumes, and looks very promising to help Linux filesystems of the future scale better. ext4 is the journalling successor to ext3. Both can upgrade smoothly from ext3, so if you want better performance from your filesystems, they're well worth looking at. In particular, if you've ever had to go through the complicated process of growing an old partition in situ, btrfs may well appeal to you.

PXELINUX and netbooting

There's also another SYSLINUX derivative, PXELINUX, which can be used to boot from a network server, after which you can install the system over the net. This can be useful for older machines which don't have a bootable CD driver, or for installing a large number of machines with the same install image. For example, check out the Ubuntu instructions for netboot using PXELINUX.

SYSLINUX and the Syslinux Project might be impressively venerable, but it's clearly also still under active development and keeping up with changes in both hardware and software. The Ubuntu install CD these days comes with EXTLINUX as an alternative to GRUB, so you can give it a try next time you're doing an install. It's also useful to have in mind for systems where GRUB causes problems, for netboot installs, or just as a more stripped-down bootloader. It's likely to stay with us for a long while to come.

Juliet Kemp has been messing around with Linux systems, for financial reward and otherwise, for about a decade. She is also the author of "Linux System Administration Recipes: A Problem-Solution Approach" (Apress, 2009).

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