1BOOT(8) System Manager's Manual BOOT(8)
2
6 boot - 2.11BSD bootstrap proceedure
7
9 The 2.11BSD system is started by a two-stage process. The first is a
10 primary bootstrap (limited to 512 bytes) which is able to read in rela‐
11 tively small stand-alone programs; the second (called boot) is used to
12 read in the system itself.
13 The primary bootstrap must reside in block zero of the boot device (the
15 disklabel resides in block one). It can be read in and started by
16 standard ROM cold boot routines or, if necessary, by keying in a small
17 startup routine. The primary bootstrap is capable of loading only type
18 0407 executable files (impure (non-shared), non-separate I&D.) Copies
19 of the block zero bootstraps are kept in the directory /mdec. Diskla‐
20 bel(8) is normally used to place a copy of the appropriate bootstrap in
21 block zero of new file systems.
22 The primary bootstrap loads boot from the file system that starts at
24 block 0 of the drive specified to the boot ROM. Normally the boot
25 device is automatically used as the root filesystem. This action can
26 be overriden by specifying the -R command to boot. If boot is not
27 found the system will hang as the primary boot spins in an endless loop
28 trying to find boot. No diagnostic message results if the file cannot
29 be found.
30 · In an emergency, the bootstrap methods described in the paper
32 Installing and Operating 2.11BSD can be used to boot from a dis‐
33 tribution tape.
34 The secondary boot program, called boot, actually brings in the system.
36 When read into location 0 and executed, boot sets up memory management,
37 relocates itself into high memory, and types its name and a `:' on the
38 console. If this is an automatic, unattended reboot, boot will use a
39 default file specification for the installation, typing the file's name
40 after the prompt. Otherwise, it reads a file specification from the
41 console. Normal line editing characters can be used to make correc‐
42 tions while typing this (see below for file specification format). If
43 only a carriage return is typed, a default name (/unix) will be used.
44 Boot finds the [specified] file and loads it into memory location zero,
45 sets up memory management as required, and calls the program by execut‐
46 ing a `trap' instruction.
47 For the system to boot, /etc/init must exist and be executable; if it
49 is not, the kernel will print a message to that effect and loop. Fur‐
50 ther, for a single user boot, the files /bin/sh and /dev/console must
51 also exist and /bin/sh must be executable (if either of these is miss‐
52 ing, init will attempt multi-user operation). For a multi-user boot
53 the file /etc/ttys must exist (if missing, init will attempt single
54 user operation).
55 Init runs the autoconfig(8) program to probe for and initialize
57 devices. Autoconfig only knows to look in /unix, thus if an alternate
58 kernel name was specified none of the devices except /dev/console and
59 the boot disk will be known.
60 If autoconfig problems are suspected (or if you are simply voyeuris‐
62 tic) the debug flag can be turned on by specifying -D to boot (see
63 below).
64 When the system is running in single user mode, it starts a single user
66 shell on the console which types a `#' prompt. After doing any file
67 system checks and setting the date (date(1)) a multi-user system can be
68 brought up by typing an EOT (control-d) in response to the `#' prompt.
69 Boot file specification format: The file specifications used with boot
71 are of the form:
72 device(ctlr,unit,part)path [-aRrDs]
74 or
76 -bootcommand
78 where
80 device is the type of the device to be searched;
82 ctlr is the controller number of the disk
84 unit is the unit number of the disk or tape;
86 part is the partition number of a filesystem on the specified disk or
88 the tape file number if the device is a tape. The underlying
89 device driver must support disklabels and a valid disklabel must
90 be present if part is anything except 0.
91 path is the path name of a disk file to be loaded with all mount pre‐
93 fixes stripped off (path must be omitted for tape files.) Tape
94 files are separated by single tape marks.
95 Flags to boot may be specified in either of two places. At the :
97 prompt and after the file name. The options are:
98 -a Ask for a kernel name. This is present for symmetry only
100 because in order to specify this option you already have to be
101 at the : prompt.
102 -D Turn on the autoconfig debug flag.
104 -R force the kernel to use its compiled in root device rather than
106 adapting to the boot device.
107 -s tell init to enter single user state rather than bringing the
109 system all the way up to multi-user mode. -r mount the root
110 filesystem read-only. This is not currently supported by the
111 kernel mostly because pipes are implemented in the filesystem.
112 Commands (-bootcommand) to boot are:
114 -bootflags N where N is a decimal number.
116 -bootflags flag where flag is from the list above.
118 -bootdebug N where N is a decimal number. This is a general
120 purpose flag word used by boot and is not passed to
121 the loaded program or kernel.
122 Device is one of the following
124 xp RM02/03/05, RP04/05/06, DIVA, SI Eagle, CDC 9766, Fuji 160
126 rp RP03
127 rk RK05
128 hk RK06/7
129 rl RL01/2
130 si RM05, CDC 9766
131 ra RA60/80/81, RX50, RD51/52/53, RC25
132 ht TU/TE16
133 tm TU/TE10
134 ts TS-11
135 The stand alone tape drive unit number is specially encoded to specify
137 both unit number and tape density (BPI). Most tape subsystems either
138 automatically adjust to tape density or have switches on the drives to
139 force the density to a particular setting, but for those which don't
140 the following density select mechanisms may be necessary. The ts only
141 operates at 1600BPI, so there is no special unit density encoding. The
142 ht will operate at either 800BPI or 1600BPI. Units 0 through 3 corre‐
143 spond to 800BPI, and 4 through 7 to 1600BPI on drives 0 through 3
144 respectively. The standard DEC tm only supports 800BPI (and hence
145 can't be used with the standard distribution tape), but several widely
146 used tm emulators support 1600BPI and even 6250BPI. Units 0 through 3
147 correspond to 800BPI, 4 through 7 to 1600BPI, and 8 through 11 to
148 6250BPI on drives 0 through 3 respectively.
149 For example, to boot a system from unit 0 on an RK07, type
151 “hk(0,0)unix” to the boot prompt. The specification “ra(1,0)unix”
152 indicates an MSCP disk, unit 1. The specification “ra(1,0,0)unix”
153 indicates an MSCP disk, unit 0 but on controller 1. And finally the
154 specification “ts(0,3)” would cause the fourth file on a tape threaded
155 on `ts' tape drive 0 to be loaded and executed.
156 Cold boot loaders: The following programs to load and execute the pri‐
158 mary bootstrap may be installed in read-only memories or manually keyed
159 into main memory. Each program is position-independent but should be
160 placed well above location 0 so it will not be overwritten. Each reads
161 a block from the beginning of a device into core location zero. The
162 octal words constituting the program are listed on the left.
163 RK (drive 0):
165 012700 mov $rkda,r0
166 177412
167 005040 clr -(r0) / rkda cleared by start
168 010040 mov r0,-(r0)
169 012740 mov $5,-(r0)
170 000005
171 105710 1: tstb (r0)
172 002376 bge 1b
173 005007 clr pc
174 RP (drive 0)
176 012700 mov $rpmr,r0
177 176726
178 005040 clr -(r0)
179 005040 clr -(r0)
180 005040 clr -(r0)
181 010040 mov r0,-(r0)
182 012740 mov $5,-(r0)
183 000005
184 105710 1: tstb (r0)
185 002376 bge 1b
186 005007 clr pc
187 TM (drive 0):
189 012700 mov $tmba,r0
190 172526
191 010040 mov r0,-(r0)
192 012740 mov $60003,-(r0)
193 060003
194 000777 br .
195
197 /unix system code
198 /boot system bootstrap
199 /etc/init system process dispatcher
200 /mdec/xxuboot sector 0 boot blocks, xx is disk type
201
203 crash(8V), autoconfig(8), reboot(2), disklabel(8), fsck(8), init(8)
2043rd Berkeley Distribution May 24, 1996 BOOT(8)