View source for Comboot/chain.c32

[[Category:Comboot]]
[[Category:Modules]]
'''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 (via partition's ID). 

All options as available in chain.c32 of Syslinux 3.85 (with some updates introduced in later versions):

'''Usage:'''
<pre>
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]
</pre>

{| border="0" cellpadding="1" cellspacing="0" bgcolor="#f9f9f9" width="100%" style="border: 1px dashed darkgray; padding: 1em; background: #f9f9f9; width: 100%; font-family: monospace; "
|+ style="text-align: left; width: 100%; white-space: nowrap; " | <code>chain.c32 options:</code> 
|-
|style="white-space: nowrap; color: #f9f9f9; visibility: hidden; display: none; height: 0px; " | <code> 123456789012345678901234567 </code>  <!-- THIS ROW SETS COLUMN1 WIDTH -->
|style="white-space: nowrap; color: #f9f9f9; visibility: hidden; display: none; height: 0px; " |  <code> THIS ROW SETS COLUMN1 WIDTH </code>  <!-- THIS ROW SETS COLUMN1 (column1 only. not column2) WIDTH -->
|-
|    <code> file=</><path/to/><loader>  </code>  
|-
| colspan="2" | &nbsp; Load file, instead of boot sector 
&nbsp; 
|-
|    <code> isolinux=<loader>  </code>  
|-
| colspan="2" | &nbsp; Load another version of ISOLINUX 
&nbsp; 
|-
|    <code> ntldr=<loader>  </code>  
|-
| colspan="2" | &nbsp; Load Windows' NTLDR, SETUPLDR.BIN or BOOTMGR, or GRLDR 
&nbsp; 
|-
|    <code> grldr=<loader>  </code>  
|-
| colspan="2" | &nbsp; Load GRUB4DOS' grldr 
&nbsp; 
|-
|    <code> cmldr=<loader>  </code>  
|-
| colspan="2" | &nbsp; Load Recovery Console of Windows NT/2K/XP 
&nbsp; 
|-
|    <code> freedos=<loader>  </code>  
|-
| colspan="2" | &nbsp; Load FreeDOS kernel.sys 
&nbsp; 
|-
|    <code> pcdos=<loader>  </code>  
|-
| colspan="2" | &nbsp; Load PC-DOS ibmbio.com 
&nbsp; 
|-
|    <code> msdos=<loader>  </code>  
|-
| colspan="2" | &nbsp; Load MS-DOS (2.xx to 6.xx) io.sys 
&nbsp; 
|-
|    <code> msdos7=<loader>  </code>  
|-
| colspan="2" | &nbsp; Load MS-DOS 7+ io.sys 
&nbsp; 
|-
|    <code> drmk=<loader>  </code>  
|-
| colspan="2" | &nbsp; Load DRMK dellbio.bin 
&nbsp; 
|-
|    <code> reactos=<loader>  </code>  
|-
| colspan="2" | &nbsp; Load ReactOS freeldr.sys 
&nbsp; 
|-
|    <code> grub=<loader>  &nbsp;[grubcfg=<config>]  </code>  
|-
| colspan="2" | &nbsp; Load grub legacy stage2 
&nbsp; 
|-
<!-- <nowiki> |    <code> seg=<segment>:<offset>:<ip>  </code>   </nowiki> -->
<!-- <nowiki> |- </nowiki> -->
<!-- <nowiki> | colspan="2" | &nbsp; Jump to <seg>:0000 instead of 0000:7C00  </nowiki> -->
<!-- <nowiki> &nbsp;  </nowiki> -->
<!-- <nowiki> |- </nowiki> -->
|    <code> swap  </code>  
|-
| colspan="2" | &nbsp; Swap drive numbers, if boot drive is not fd0/hd0 
&nbsp; 
|-
|    <code> hide  </code>  
|-
| colspan="2" | &nbsp; Hide primary partitions, except selected partition 
<!-- &nbsp;  -->
<!-- <nowiki> |- </nowiki> -->
<!-- <nowiki> |    <code> sethidden  </code>   </nowiki> -->
<!-- <nowiki> |- </nowiki> -->
<!-- <nowiki> | colspan="2" | &nbsp; Set the FAT/NTFS hidden sectors field  </nowiki> -->
|}

See [[doc/chain]] for more options.

== Numbering of Drives and Partitions ==


=== Drive numbering ===

Hard drive numbering starts at 0:
* <tt>'''hd0'''</tt> : first hard drive (as seen by the BIOS)
* <tt>'''hd1'''</tt> : second hard drive
* <tt>'''hd2'''</tt> : third hard drive
* ...

Floppy drive numbering starts at 0:
* <tt>'''fd0'''</tt> : first floppy drive
* <tt>'''fd1'''</tt> : second floppy drive

The drive from which Syslinux is booted can be referred to with the parameter:
* <tt>'''boot'''</tt>

The drive and partition from which Syslinux is booted can be referred to with the parameter:
* <tt>'''fs'''</tt>

Find partition by uuid or label in all GPT partitions on all available drives:
* <tt>'''label'''=''mylabel''</tt>
* <tt>'''guid'''=''myguid''</tt>
Note that '''label''' and '''guid''' work only on GPT partition tables; it is not ''filesystem'' but ''partition'' label and guid.


=== Partition numbering ===

The physical devices are counted starting at zero. 
The partitions are counted starting at one.

In a GPT scheme, there are only "primary" partitions. 
Usually up to a maximum of 128 primary partitions can be created in one GPT device 
(the specification allows for more; it requires appropriate conditions).

In a "DOS" (aka. "traditional" or "legacy" or "MBR") partition table scheme, 
a maximum of 4 "primary" partitions can be created, 
or alternatively up to 3 "primary" partitions and one "extended" partition, 
the latter containing "logical" partitions.

Please note that for devices with a traditional MBR ("DOS") partition table scheme, 
{{nowrap|"<tt>chain.c32</tt>"}} counts the "logical" partitions 
starting from "five", even if not all "primary" slots are in used.

GPT partitions are simply counted in order, starting at one.


Partition numbers (short):
* 0 : MBR (default.)
:* 1-4 : primary partitions
::* 5 and higher : logical partitions


Partition numbers (long):
* <tt>'''0'''</tt> : '''MBR''' (default)
:* <tt>'''1'''</tt> : first '''primary''' partition
:* <tt>'''2'''</tt> : second primary partition
:* <tt>'''3'''</tt> : third primary partition
:* <tt>'''4'''</tt> : fourth primary partition
::* <tt>'''5'''</tt> : first '''logical''' partition
::* <tt>'''6'''</tt> : second logical partition
::* <tt>'''7'''</tt> : third logical partition
::* <tt>'''8'''</tt> : fourth logical partition
::* <tt>'''9'''</tt> : fifth logical partition
::* <tt>'''10'''</tt> : sixth logical partition
::* <tt>'''11'''</tt> : seventh logical partition
::* <tt>'''12'''</tt> : eighth logical partition
::* ...

{| cellpadding="10" cellspacing="1" style="text-align:center; padding: 1em; border-style: solid; border-width: 1px;"
|+ style="text-align: left; width: 100%; white-space: nowrap; " | <code>Partition Numbering:</code> 
! scope="col" | First disk<br />as seen by BIOS 
! scope="col" bgcolor="#FFFF00" | PRIMARY 
! scope="col" bgcolor="#FFFF00" | LOGICAL 
! scope="col" colspan="3" | Numbering
|-
| scope="row" bgcolor="#E6E6FA" | hd0 
| 
| 
| bgcolor="#E6E64C" | 0 
| colspan="2" bgcolor="#FFFF99" style="text-align:left;font-weight: light;" | (MBR) 
|-
| scope="row" bgcolor="#E6E6FA" | hd0 1 
| scope="row" bgcolor="#FFFF99" style="text-align:left; font-weight: light;" | First 
| 
| 
| bgcolor="#E6E64C" | 1 
|
|-
| scope="row" bgcolor="#E6E6FA" | hd0 2 
| scope="row" bgcolor="#FFFF99" style="text-align:left; font-weight: light;" | Second 
| 
| 
| bgcolor="#E6E64C" | 2 
|
|-
| scope="row" bgcolor="#E6E6FA" | hd0 3 
| scope="row" bgcolor="#FFFF99" style="text-align:left; font-weight: light;" | Third 
| 
| 
| bgcolor="#E6E64C" | 3 
|
|-
| scope="row" bgcolor="#E6E6FA" | hd0 4 
| scope="row" bgcolor="#FFFF99" style="text-align:left; font-weight: light;" | Fourth 
| 
| 
| bgcolor="#E6E64C" | 4 
|
|-
| scope="row" bgcolor="#E6E6FA" | hd0 5 
| 
| scope="row" bgcolor="#FFFF99" style="text-align:left; font-weight: light;" | First 
| 
| 
| bgcolor="#E6E64C" | 5 
|-
| scope="row" bgcolor="#E6E6FA" | hd0 6 
| 
| scope="row" bgcolor="#FFFF99" style="text-align:left; font-weight: light;" | Second 
| 
| 
| bgcolor="#E6E64C" | 6 
|-
| scope="row" bgcolor="#E6E6FA" | hd0 7 
| 
| scope="row" bgcolor="#FFFF99" style="text-align:left; font-weight: light;" | Third 
| 
| 
| bgcolor="#E6E64C" | 7 
|-
| scope="row" bgcolor="#E6E6FA" | hd0 8 
| 
| scope="row" bgcolor="#FFFF99" style="text-align:left; font-weight: light;" | Fourth 
| 
| 
| bgcolor="#E6E64C" | 8 
|-
| scope="row" bgcolor="#E6E6FA" | hd0 9 
| 
| scope="row" bgcolor="#FFFF99" style="text-align:left; font-weight: light;" | Fifth 
| 
| 
| bgcolor="#E6E64C" | 9 
|-
| scope="row" bgcolor="#E6E6FA" | hd0 10 
| 
| scope="row" bgcolor="#FFFF99" style="text-align:left; font-weight: light;" | Sixth 
| 
| 
| bgcolor="#E6E64C" | 10 
|-
| scope="row" bgcolor="#E6E6FA" style="font-weight: light;" | hd0 ... 
| 
| scope="row" bgcolor="#FFFF99" style="text-align:left; font-weight: light;" | ... 
| 
| 
| bgcolor="#E6E64C" style="font-weight: light;" | ... 
|}

=== Examples ===

<pre>
UI menu.c32

LABEL boot_hd0
MENU LABEL Boot from first hard drive
COM32 chain.c32
APPEND hd0

LABEL boot_hd1
MENU LABEL Boot from second hard drive
COM32 chain.c32
APPEND hd1

LABEL boot_fd0
MENU LABEL Boot from first floppy drive
COM32 chain.c32
APPEND fd0

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

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

LABEL boot_hd2_2
MENU LABEL Boot second primary partition from third 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 ntldr from GPT partition labelled "win7fs"
COM32 chain.c32
APPEND label=win7fs ntldr=/bootmgr
</pre>

== mbr ==

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):
<pre>
$ hexdump -s 440 -n 4 -e '"0x%08x\n"' /dev/sda
0x0ec8694c
</pre>
Or by running:
<pre>
$ fdisk -l /dev/sda
...
Disk identifier: 0x0ec8694c
</pre>
Example:
<pre>
LABEL mbr_serial
COM32 chain.c32
APPEND mbr:0x0ec8694c
</pre>


== Options ==

The following are some popular options available for chain.c32. 
See [[doc/chain]] for more options.

''' file=<loader> '''
:Load the file <loader> <u>from the SYSLINUX filesystem</u> instead of loading the boot sector.
<!-- -->
<!-- This is not a "popular" option -->
<!-- ''' seg=<segment> ''' -->
<!-- :loads at and jumps to <segment>:0000 instead of 0000:7C00. -->

''' isolinux=<loader> '''
:Load another version/build of the ISOLINUX bootloader <!--
--> and patch the loader with appropriate parameters in memory. <!--
--> This avoids the need for the {{nowrap|-eltorito-alt-boot}} <!--
--> parameter of mkisofs, when more than one ISOLINUX per CD/DVD is needed.

''' ntldr=<loader> '''
:Equivalent to {{nowrap|1=<tt>file=<loader> seg=0x2000 setbpb nohand</tt>}}
:Used with WinNT's loaders
::Example loaders: NTLDR (XP, 2003), BOOTMGR (Vista, 2008, 7), GRLDR (Grub4DOS).
::See: [[HowTos]] & [[Linux_and_Windows_deployment|Linux and Windows deployment]]

''' grldr=<loader> '''
:Load GRUB4DOS grldr, performing additional corrections on the file in memory.

''' cmldr=<loader> '''
:Equivalent to {{nowrap|1=<tt>ntldr=<loader> & "cmdcons\0"</tt>}}
:Used with Recovery Console of Windows NT/2K/XP, <!--
--> written to the system name field in the bootsector.

''' freedos=<loader> '''
:Equivalent to {{nowrap|1=<tt>file=<loader> seg=0x60 sect=0x1FE0 setbpb nohand</tt>}}
:Used with FreeDOS' kernel.sys

''' pcdos=<loader> '''
:Equivalent to {{nowrap|1=<tt>file=<loader> seg=0x70 sect=0x8000 setbpb nohand</tt>}}
:Used with PC-DOS' ibmbio.com

''' msdos=<loader> '''
:Equivalent to {{nowrap|1=<tt>file=<loader> seg=0x70 sect=0x8000 setbpb nohand</tt>}}
:Used with MS-DOS (v.2.xx to 6.xx)' io.sys


''' msdos7=<loader> '''
:Equivalent to {{nowrap|1=<tt>file=<loader> seg=0x70:0:0x200 sect=0x8000 setbpb nohand</tt>}}
:Used with MS-DOS v.7+' io.sys

''' drmk=<loader> '''
:Equivalent to {{nowrap|1=<tt>file=<loader> seg=0x70 sect=0x2000 setbpb nohand</tt>}}
:Used with DRMK' dellbio.bin

''' reactos=<loader> '''
:{{V|6.04+}}Equivalent to {{nowrap|1=<tt>file=<loader> seg=0x0F80 setbpb nohand</tt>}}
:Used with ReactOS' freeldr.sys. <!--
--> Add 'save' option so as to store corrected BPB values.

''' grub=<loader> [grubcfg=<myconfig>] '''
:{{V|4.02+}}Equivalent to {{nowrap|1=<tt>file=<loader> seg=0x800::0x200 nohand nosect grub</tt>}}
:Used with grub legacy's stage2, performing additional corrections on the file in memory. <!--
--> Optionally, an alternative config file can be specified via the 'grubcfg' option.

''' swap '''
:If the drive is not fd0/hd0, install a BIOS stub which swaps the drive numbers.

''' hide '''
: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.

<!-- This is not a "popular" option, and it is no longer valid -->
<!-- ''' sethidden ''' -->
<!-- :update the "hidden sectors" (partition offset) field in a FAT/NTFS boot sector. -->

== UEFI ==

In UEFI, the boot process is slightly different than in BIOS. For booting the system, UEFI does not use traditional boot records, but rather {{nowrap|efi-compatible}} {{nowrap|files/images}}.

When using UEFI mode, there are no such things as chaining to a traditional {{nowrap|MBR/VBR}} or loading a file that is not {{nowrap|efi-compatible}}.

As of version 6.03, <tt>{{nowrap|chain.c32}}</tt> cannot chainload {{nowrap|efi-compatible}} files, so there is no practical use of it in UEFI mode.

When using CSM mode (aka "legacy" or "BIOS" mode) in a UEFI system, <tt>{{nowrap|chain.c32}}</tt> should work as in a traditional BIOS-based hardware, provided that the adequate binary is being used (from the "BIOS" firmware architecture, not from "EFI") and that the firmware correctly and fully supports CSM mode.


== See Also ==

* [[doc/chain]]
* [[DRMK]]
* BPB: [https://en.wikipedia.org/wiki/BIOS_parameter_block BIOS Parameter Block]