ref: a5cb451b299b03f44154fac5780b6a57ca130ce0
dir: /man/10/9load/
.TH 9LOAD 10.8 .SH NAME 9load, ld, 9pxeload \- PC bootstrap program .SH SYNOPSIS .I "(Under MS-DOS) .br [ .I drive :][ .I path .RB ] ld [ .I 9load ] .SH DESCRIPTION On the PC, bootstrap programs from Plan 9 are used to boot Inferno as well (hence the naming convention). .I 9load and .I ld are programs that reside in a FAT file system and bootstrap Inferno. .I 9load loads the kernel, but it cannot be run from DOS; use .I ld to bootstrap (by starting .IR 9load ) if DOS is running. .I 9load is run automatically by the boot procedures described below; it cannot be run directly by hand. There are three bootstrap sequences: .IP \- BIOS, MBR, disk partition PBS, .IR 9load , kernel .IP \- BIOS, floppy PBS, .IR 9load , kernel .IP \- BIOS, MBR, DOS, .IR ld , .IR 9load , kernel. .PP Details follow. .PP .I 9load is a bootstrap program that loads and starts a program, typically the kernel, on a PC. It is run by the PC partition boot sector program (PBS), which usually resides in the first sector of the active partition. A copy of the Plan 9 PBS is kept in .BR /Inferno/386/pbs , but due to the ``cylinder-head-sector'' (CHS) addressing mode of old BIOSes, it can only operate up to 8.5GB into the disk. Plan 9 partitions further into the disk can only be booted using .BR /Inferno/386/pbslba , and then only if the machine's BIOS supports linear block addressing (LBA) mode for disk transfers. .PP When booting from floppy or hard disk, the BIOS loads the first sector of the medium at location 0x7C00. In the case of a floppy, this is the PBS. In the case of a hard disk it it the master boot record (MBR). The MBR copies itself to address .BR 0x600 , finds the active partition and loads its PBS at address .BR 0x7C00 . A copy of the Plan 9 MBR is kept in .BR /Inferno/386/mbr ; some commercial MBRs cannot read sectors past 2GB. The Plan 9 MBR can read sectors up to 8.5GB into the disk, and further if the BIOS supports LBA. The single file .B /Inferno/386/mbr detects whether the BIOS supports LBA and acts appropriately, defaulting to CHS mode when LBA is not present. The PBSs cannot do this due to code size considerations. The Plan 9 MBR is suitable for booting non-Plan 9 operating systems, and (modulo the large disk constraints just described) non-Plan 9 MBRs are suitable for booting Plan 9. .PP Thus the default sequence is: BIOS, MBR, PBS, .IR 9load , kernel. .PP Because it contains many device drivers for different disks and networks, .I 9load is larger than 64K and cannot be run as a DOS .RB `` .com '' executable. A stripped-down version that knows about disks but not networks, called .I ld (really .BR ld.com ), fits in 64K and can be used under DOS to load and start a program (default .IR 9load ) from the FAT16 partition. Its command line argument is of the same format as the .I bootfile specifiers described below. This profusion of loaders is unfortunate, but at least .I ld and .I 9load are compiled from the same source. .PP .I 9load begins execution at address .B 0x80010000 (64K) and loads the .I bootfile at the entry address specified by the header, usually .BR 0x80100020 . After loading, control is passed to the entry location. .PP Finally, .I 9pxeload is a version of .I 9load that can be booted using the PXE download found on some ethernet card BIOSs. .PP In summary, Inferno and Plan 9 can be booted on a PC three different ways: either by booting MS-DOS and using .I ld to start .I 9load in the appropriate directory, by booting directly from an Inferno/Plan 9 boot floppy or disk partition prepared using .B format to install the appropriate files and bootstrap sectors (see .IR prep (8)), or by using a PXE capable BIOS to boot .I 9pxeload directly over the ethernet. .PP The .IR bootfile , which may be compressed with .IR gzip (1), can be specified to .I 9load as a .B bootfile= entry in .IR plan9.ini , or if booting from the ethernet, by a BOOTP server. If the .B plan9.ini file contains multiple .B bootfile= entries, .I 9load will present a numerical menu of the choices; type the corresponding number to select an entry. .PP The format of the .I bootfile name is .IB device ! file or .IB device ! partition ! file\f1. If .BI ! file is omitted, the default for the particular .I device is used. Supported .I devices are .TF \fLethern .TP .BI fd n An MS-DOS floppy disk. .I N specifies the floppy drive, either 0 or 1. The .I bootfile is the contents of the MS-DOS .IR file . There is no default file. For compatibility with hard disks, a .I partition may be given, but only .B dos is recognized: .BI fd0!dos! file\f1. .TP .BI ether n Ethernet. .I N specifies the Ethernet device number. If a .I partition is specified, it is taken to be the name of a host machine from which to load the kernel. .I file is determined by the .B /lib/ndb (see .IR ndb (6)) entry for this PC. .TP .BI sd Cn Non-floppy disk. The device name format is described in .IR sd (3). A .I partition must be given and must name a partition containing a FAT file system. The name .B dos refers to the first DOS partition on a given device. It is common for Inferno/Plan 9 partitions to contain a small FAT file system for configuration. By convention, this partition is called .BR 9fat . There is no default partition or pathname. .PD .PP When .I 9load starts running at physical address 0x10000, it switches to 32-bit mode. It then double maps the first 16Mb of physical memory to virtual addresses 0 and 0x80000000. Physical memory from 0x300000 upwards is used as data space. Next, in order to find configuration information, .I 9load searches all units on devices .BR fd and .BI sd Cn \fR, in that order, for a file called .B plan9\eplan9.ini or .B plan9.ini (see .IR plan9.ini (10.6)) on a partition named .B dos or .BR 9fat . If one is found, searching stops and the file is read into memory at physical address 0x1200 where it can be found later by any loaded .IR bootfile . Some options in .B plan9.ini are used by .IR 9load : .TF bootfile=manual .TP .B console .TP .B baud Specifies the console device and baud rate if not a display. .TP .BI ether n Ethernet interfaces. These can be used to load the .I bootfile over a network. Probing for Ethernet interfaces is too prone to error. .TP .BI bootfile= bootfile Specifies the .IR bootfile . This option is overridden by a command-line argument. .TP .B bootfile=auto Default. .TP .B bootfile=local Like .IR auto , but do not attempt to load over the network. .TP .B bootfile=manual After determining which devices are available for loading from, enter prompt mode. .PD .PP When the search for .B plan9.ini is done, .I 9load proceeds to determine which bootfile to load. If there was no .I bootfile option, .I 9load chooses a default from the following prioritized device list: .EX fd sd ether .EE .I 9load then attempts to load the .I bootfile unless the .B bootfile=manual option was given, in which case prompt mode is entered immediately. If the default device is .BR fd , .I 9load will prompt the user for input before proceeding with the default bootfile load after 5 seconds; this prompt is omitted if a command-line argument or .I bootfile option was given. .PP .I 9load prints the list of available .IR device s and enters prompt mode on encountering any error or if directed to do so by a .B bootfile=manual option. In prompt mode, the user is required to type a .IB bootfile in response to the .L "Boot from: prompt. .PP .I 9load parses the master boot record and Plan 9 partition tables (see .IR prep (8)), leaving partitioning information appended to the in-memory contents of .I plan9.ini for the .IR bootfile . This is used by .IR sd (3) to initialize partitions so that a file system in a partition can be found and mounted as the root file system. A more extensive partitioning is typically done by system initialisation in .B osinit.dis (see .IR root (3)). .PP A control-P character typed at any time on the console causes .B 9load to perform a hardware reset (Ctrl-Alt-Del can also be used on a PC keyboard). .PP When loaded from a PBS (rather than from .IR ld.com ), .I 9load must be contiguously allocated on the disk. See .IR dossrv (4) for information on ensuring this. .SH FILES .RI [ drive :] [ .I path .RB ] 9load .br .RI [ drive :] [ .I path .RB ] ld .br .IB "FAT filesystem" :\eplan9\eplan9.ini .br .IB "FAT filesystem" :\eplan9.ini .SH SOURCE .B /os/boot/pc .SH "SEE ALSO" .IR plan9.ini (10.6), .IR prep (8) .SH BUGS Much of the work done by .B 9load is duplicated by the loaded kernel. .PP If .I ld detects an installed MS-DOS Extended Memory Manager, it attempts to de-install it, but the technique used may not always work. It is safer not to install the Extended Memory Manager before running .IR ld .