BOOT(8) 						      System Manager's Manual							   BOOT(8)

NAME

       boot - 2.11BSD bootstrap proceedure

DESCRIPTION

       The  2.11BSD  system  is  started by a two-stage process.  The first is a primary bootstrap (limited to 512 bytes) which is able to read in
       relatively small stand-alone programs; the second (called boot) is used to read in the system itself.

       The primary bootstrap must reside in block zero of the boot device (the disklabel resides in block one).  It can be read in and started	by
       standard  ROM  cold boot routines or, if necessary, by keying in a small startup routine.  The primary bootstrap is capable of loading only
       type 0407 executable files (impure (non-shared), non-separate I&D.)  Copies of the block zero bootstraps are kept in the  directory  /mdec.
       Disklabel(8) is normally used to place a copy of the appropriate bootstrap in block zero of new file systems.

       The  primary  bootstrap	loads  boot from the file system that starts at block 0 of the drive specified to the boot ROM.  Normally the boot
       device is automatically used as the root filesystem.  This action can be overriden by specifying the -R command to boot.  If  boot  is  not
       found  the  system  will  hang as the primary boot spins in an endless loop trying to find boot.  No diagnostic message results if the file
       cannot be found.

       o      In an emergency, the bootstrap methods described in the paper Installing and Operating 2.11BSD can be used to boot from a  distribu-
	      tion tape.

       The  secondary  boot program, called boot, actually brings in the system.  When read into location 0 and executed, boot sets up memory man-
       agement, relocates itself into high memory, and types its name and a `:' on the console.  If this is an automatic, unattended reboot,  boot
       will use a default file specification for the installation, typing the file's name after the prompt.  Otherwise, it reads a file specifica-
       tion from the console.  Normal line editing characters can be used to make corrections while typing this (see below for file  specification
       format).   If only a carriage return is typed, a default name (/unix) will be used.  Boot finds the [specified] file and loads it into mem-
       ory location zero, sets up memory management as required, and calls the program by executing a `trap' instruction.

       For the system to boot, /etc/init must exist and be executable; if it is not, the kernel will print a message  to  that	effect	and  loop.
       Further,  for  a single user boot, the files /bin/sh and /dev/console must also exist and /bin/sh must be executable (if either of these is
       missing, init will attempt multi-user operation).  For a multi-user boot the file /etc/ttys must exist (if missing, init will attempt  sin-
       gle user operation).

       Init runs the autoconfig(8) program to probe for and initialize devices.  Autoconfig only knows to look in /unix, thus if an alternate ker-
       nel name was specified none of the devices except /dev/console and the boot disk will be known.

       If autoconfig problems are suspected (or if  you are simply voyeuristic) the debug flag can be turned on by  specifying	-D  to	boot  (see
       below).

       When  the  system  is  running in single user mode, it starts a single user shell on the console which types a `#' prompt.  After doing any
       file system checks and setting the date (date(1)) a multi-user system can be brought up by typing an EOT (control-d) in response to the `#'
       prompt.

       Boot file specification format: The file specifications used with boot are of the form:

	      device(ctlr,unit,part)path [-aRrDs]

       or

	      -bootcommand

       where

       device is the type of the device to be searched;

       ctlr   is the controller number of the disk

       unit   is the unit number of the disk or tape;

       part   is  the  partition  number  of  a  filesystem on the specified disk or the tape file number if the device is a tape.  The underlying
	      device driver must support disklabels and a valid disklabel must be present if part is anything except 0.

       path   is the path name of a disk file to be loaded with all mount prefixes stripped off (path must be omitted for tape files.)	Tape files
	      are separated by single tape marks.

       Flags to boot may be specified in either of two places.	At the : prompt and after the file name.  The options are:

       -a     Ask  for	a  kernel name.  This is present for symmetry only because in order to specify this option you already have to be at the :
	      prompt.

       -D     Turn on the autoconfig debug flag.

       -R     force the kernel to use its compiled in root device rather than adapting to the boot device.

       -s     tell init to enter single user state rather than bringing the system all the way up to multi-user mode.  -r mount the root  filesys-
	      tem read-only.  This is not currently supported by the kernel mostly because pipes are implemented in the filesystem.

       Commands (-bootcommand) to boot are:

       -bootflags N	   where N is a decimal number.

       -bootflags flag	   where flag is from the list above.

       -bootdebug N	   where  N is a decimal number.  This is a general purpose flag word used by boot and is not passed to the loaded program
			   or kernel.

       Device is one of the following

	    xp	 RM02/03/05, RP04/05/06, DIVA, SI Eagle, CDC 9766, Fuji 160
	    rp	 RP03
	    rk	 RK05
	    hk	 RK06/7
	    rl	 RL01/2
	    si	 RM05, CDC 9766
	    ra	 RA60/80/81, RX50, RD51/52/53, RC25
	    ht	 TU/TE16
	    tm	 TU/TE10
	    ts	 TS-11

       The stand alone tape drive unit number is specially encoded to specify both unit number and  tape  density  (BPI).   Most  tape	subsystems
       either  automatically  adjust  to  tape	density or have switches on the drives to force the density to a particular setting, but for those
       which don't the following density select mechanisms may be necessary.  The ts only operates at 1600BPI, so there is no special unit density
       encoding.  The ht will operate at either 800BPI or 1600BPI.  Units 0 through 3 correspond to 800BPI, and 4 through 7 to 1600BPI on drives 0
       through 3 respectively.	The standard DEC tm only supports 800BPI (and hence can't be used with the standard  distribution tape), but  sev-
       eral  widely  used  tm  emulators  support 1600BPI and even 6250BPI.  Units 0 through 3 correspond to 800BPI, 4 through 7 to 1600BPI, and 8
       through 11 to 6250BPI on drives 0 through 3 respectively.

       For example, to boot a system from unit 0 on an RK07, type "hk(0,0)unix" to the boot prompt.  The specification "ra(1,0)unix" indicates	an
       MSCP  disk,  unit  1.  The specification "ra(1,0,0)unix" indicates an MSCP disk, unit 0 but on controller 1.  And finally the specification
       "ts(0,3)" would cause the fourth file on a tape threaded on `ts' tape drive 0 to be loaded and executed.

       Cold boot loaders: The following programs to load and execute the primary bootstrap may be installed  in  read-only  memories  or  manually
       keyed  into  main  memory.   Each program is position-independent but should be placed well above location 0 so it will not be overwritten.
       Each reads a block from the beginning of a device into core location zero.  The octal words constituting the  program  are  listed  on  the
       left.

       RK (drive 0):
	  012700      mov     $rkda,r0
	  177412
	  005040      clr     -(r0)	     / rkda cleared by start
	  010040      mov     r0,-(r0)
	  012740      mov     $5,-(r0)
	  000005
	  105710  1:  tstb    (r0)
	  002376      bge     1b
	  005007      clr     pc

       RP (drive 0)
	  012700      mov     $rpmr,r0
	  176726
	  005040      clr     -(r0)
	  005040      clr     -(r0)
	  005040      clr     -(r0)
	  010040      mov     r0,-(r0)
	  012740      mov     $5,-(r0)
	  000005
	  105710  1:  tstb    (r0)
	  002376      bge     1b
	  005007      clr     pc

       TM (drive 0):
	  012700      mov     $tmba,r0
	  172526
	  010040      mov     r0,-(r0)
	  012740      mov     $60003,-(r0)
	  060003
	  000777      br      .

FILES

       /unix	       system code
       /boot	       system bootstrap
       /etc/init       system process dispatcher
       /mdec/xxuboot   sector 0 boot blocks, xx is disk type

SEE ALSO

       crash(8V), autoconfig(8), reboot(2), disklabel(8), fsck(8), init(8)

3rd Berkeley Distribution					   May 24, 1996 							   BOOT(8)