1BOOT(8) System Manager's Manual BOOT(8)
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6 boot - 2.11BSD bootstrap proceedure
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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