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Revision as of 16:43, 16 April 2011 by Gerth (talk | contribs) (Options: Use the right name for PC-DOS: instead of io.sys + add MS- and PC- before DOS)

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chain.c32 is a COM32 module for Syslinux. It can chainload MBRs, partition boot sectors, Windows bootloaders (ntldr, setupldr.bin and bootmgr), MS-DOS and PC-DOS io.sys, Freedos kernel.sys, isolinux.bin (only from ISOLINUX), grldr of grub4dos or a bootsector saved to a file. It can also swap BIOS drive numbers or hide partitions.

All options as available in chain.c32 of Syslinux 3.85:

Usage:   chain.c32 hd<disk#> [<partition>] [options]
         chain.c32 fd<disk#> [options]
         chain.c32 mbr:<id> [<partition>] [options]
         chain.c32 boot [<partition>] [options]
         chain.c32 fs [options]
         chain.c32 label=<label> [options]
         chain.c32 guid=<label> [options]

Options: file=<loader>      load file, instead of boot sector
         isolinux=<loader>  load another version of ISOLINUX
         ntldr=<loader>     load Windows NTLDR, SETUPLDR.BIN or BOOTMGR
         cmldr=<loader>     load Recovery Console of Windows NT/2K/XP
         freedos=<loader>   load FreeDOS kernel.sys
         msdos=<loader>     load MS-DOS io.sys
         pcdos=<loader>     load PC-DOS
         seg=<segment>      jump to <seg>:0000 instead of 0000:7C00
         swap               swap drive numbers, if bootdisk is not fd0/hd0
         hide               hide primary partitions, except selected partition
         sethidden          set the FAT/NTFS hidden sectors field

Numbering of Drives and Partitions

Drive numbering

Hard drive numbering starts at 0:

  • hd0 : first hard drive (as seen by the BIOS)
  • hd1 : second hard drive
  • hd2 : third hard drive
  • ...

Floppy drive numbering starts at 0:

  • fd0 : first floppy drive
  • fd1 : second floppy drive

The drive from which Syslinux is booted can be referred to with the parameter:

  • boot

The drive and partition from which Syslinux is booted can be referred to with the parameter:

  • fs

Find partition by uuid or label in all GPT partitions on all available drives:

  • label=label
  • guid=guid

Note that label and guid works only on GPT partition tables, it is not filesystem but partition label and uuid.

Partition numbering

Partition numbers (short):

  • 0 : MBR (default.)
  • 1-4 : primary partitions
  • 5 and higher : logical partitions

Partition numbers (long):

  • 0 : MBR (default)
  • 1 : first primary partition
  • 2 : second primary partition
  • 3 : third primary partition
  • 4 : fourth primary partition
  • 5 : first logical partition
  • 6 : second logical partition
  • 7 : third logical partition
  • 8 : fourth logical partition
  • 9 : fifth logical partition
  • 10 : sixth logical partition
  • 11 : seventh logical partition
  • 12 : eighths logical partition
  • ...


UI menu.c32

LABEL boot_hd0
MENU LABEL Boot from first hard drive
COM32 chain.c32

LABEL boot_hd1
MENU LABEL Boot from second hard drive
COM32 chain.c32

LABEL boot_fd0
MENU LABEL Boot from first floppy drive
COM32 chain.c32

LABEL boot_syslinux_drive
MENU LABEL Boot the drive from which Syslinux is booted (hard drive or floppy drive)
COM32 chain.c32

LABEL boot_syslinux_filesystem
MENU LABEL Boot the filesystem from which Syslinux is booted (partition in hard drive or floppy drive)
COM32 chain.c32

LABEL boot_hd2_2
MENU LABEL Boot second primary partition from thirth hard drive
COM32 chain.c32
APPEND hd2 2

LABEL boot_hd1_5
MENU LABEL Boot first logical partition from second hard drive
COM32 chain.c32
APPEND hd1 5

LABEL boot_hd3_0
MENU LABEL Boot MBR of fourth hard drive (same as "APPEND hd3")
COM32 chain.c32
APPEND hd3 0

LABEL boot_part_win7fs
MENU LABEL Boot ntld from GPT partition labelled "win7fs"
COM32 chain.c32
APPEND label=win7fs ntldr=/bootmgr


The mbr: syntax means search all the hard disks until one with a specific MBR serial number (bytes 440-443) is found.

You can get the MBR serial number, by running the following command (change /dev/sda to the correct device):

$ hexdump -s 440 -n 4 -e '"0x%08x\n"' /dev/sda

Or by running:

$ fdisk -l /dev/sda
Disk identifier: 0x0ec8694c


LABEL mbr_serial
COM32 chain.c32
APPEND mbr:0x0ec8694c



loads the file <loader> **from the SYSLINUX filesystem** instead of loading the boot sector.


loads at and jumps to <seg>:0000 instead of 0000:7C00.


Chainload another version/build of the ISOLINUX bootloader and patch the loader with appropriate parameters in memory. This avoids the need for the -eltorito-alt-boot parameter of mkisofs, when you want more than one ISOLINUX per CD/DVD.


equivalent to seg=0x2000 file=<loader> sethidden, used with WinNT's loaders
Example loaders: NTLDR (XP, 2003), BOOTMGR (Vista, 2008, 7), GRLDR (Grub4DOS).
See: HowTos & Linux and Windows deployment


used with Recovery Console of Windows NT/2K/XP. same as ntldr=<loader> & "cmdcons\0" written to the system name field in the bootsector.


equivalent to seg=0x60 file=<loader> sethidden, used with FreeDOS kernel.sys.


equivalent to seg=0x70 file=<loader> sethidden, used with MS-DOS' io.sys.


equivalent to seg=0x70 file=<loader> sethidden, used with PC-DOS'


if the disk is not fd0/hd0, install a BIOS stub which swaps the drive numbers.


change type of primary partitions with IDs 01, 04, 06, 07, 0b, 0c, or 0e to 1x, except for the selected partition, which is converted the other way.


update the "hidden sectors" (partition offset) field in a FAT/NTFS boot sector.