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FreeBSD/Linux Kernel Cross Reference
sys/boot/README

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    1 $FreeBSD: src/sys/boot/README,v 1.4 2005/01/05 22:16:10 imp Exp $
    2 
    3        README file, for the boot config file setup.  This is meant
    4        to explain how to manage the loader configuration process.
    5        The boot and loading process is either defined, or being
    6        defined in boot(8) and loader(8).
    7 
    8        The ongoing development of the FreeBSD bootloader, and its
    9        rapid deployment while still in the development phase, has
   10        resulted in a large number of installations with outdated
   11        configurations.  Those installations actively tracking the
   12        FreeBSD development should also ensure that their bootloader
   13        configurations are updated.  If you see files discussed here
   14        that your system doesn't yet have, add them yourself.
   15 
   16        This is an effort to give the currently correct method for
   17        setting up your boot process.  It includes information on
   18        setting up screen savers and plug and play information, and
   19        also on recording any changes you make in your kernel
   20        configuration.  This file is temporary, because as I noted,
   21        the process is still undergoing development, and will still
   22        change.  Man pages are coming out, but they're still going
   23        to be somewhat fragile for a while.  If you note anything in
   24        here that's broken, it would be a good idea to report it to
   25        the FreeBSD-current list, or to Daniel C. Sobral
   26        <dcs@FreeBSD.org> or Mike Smith <msmith@FreeBSD.org>.
   27 
   28        After the first two stages in the booting process (described
   29        in boot(8)), the last stage of the booting process, called
   30        the loader (see loader(8)) reads in the /boot/loader.rc
   31        file.  The two lines you should have there are:
   32 
   33        include /boot/loader.4th
   34        start
   35 
   36        This reads the ficl (forth) initialization files, then
   37        /boot/default/loader.conf.  This file, which strongly
   38        resembles in form /etc/rc.conf but functions quite
   39        differently, has spots for endless user customization but
   40        isn't yet completely finished.  For one thing, it used to
   41        assume a /kernel.config instead of a /boot/kernel.conf.
   42        Watch the first few lines of /boot/defaults/loader.conf to
   43        see if the file name changes.
   44 
   45        [See the section at the end on loader.conf syntax]
   46 
   47        You don't actually want to make any changes to
   48        /boot/defaults/loader.conf, the file that is a  hacking-
   49        target is:
   50 
   51        /boot/loader.conf
   52 
   53        and might very likely not exist yet on your system).  You
   54        should copy /boot/defaults/loader.conf to /boot/loader.conf,
   55        and then cut out anything you didn't want changed.
   56 
   57        The start command also loads your kernel for you, so don't
   58        put any lines in there like "load kernel", they'll fail (but
   59        really have already worked for you).  Start also reads in
   60        the file /boot/defaults/loader.conf and /boot/loader.conf.
   61        If you don't have /boot/loader.conf, you'll see a message on
   62        boot about it, but it's a warning only, no other effects.
   63        See the section on loader.conf syntax at the end of this
   64        document, for some more pointers on loader.conf syntax.
   65 
   66        The best way to manage splash screens is with entries in
   67        /boot/loader.conf, and this is very clearly illustrated in
   68        /boot/defaults/loader.conf (which you could just copy over
   69        to /boot/loader.conf).  I'm going to illustrate here how you
   70        *could* do it in /boot/loader.rc (for information only)
   71        but I don't recommend you do this; use the
   72        /boot/defaults/loader.conf syntax, it's easier to get it
   73        correct.
   74 
   75        You can load your splash screen by putting the following
   76        lines into /boot/loader.rc:
   77 
   78        load splash_bmp
   79        load -t splash_image_data /path/to/file.bmp
   80 
   81        The top line causes the splash_bmp module to get loaded.
   82        The second line has the parameter "-t" which tells the
   83        loader that the class of DATA being loaded is not a module,
   84        but instead a splash_image_data located in file
   85        /path/to/file.bmp.
   86 
   87        To get your plug and play data correctly set, run kget,
   88        redirecting the output to /boot/kernel.conf.  Note that kget
   89        right now adds an extra "q" to it's output (from the q for
   90        quit you press when you exit config), and if you want, you
   91        can remove that from the file.  Kget reports data only, so
   92        feel free to run it, just to see the output.  Make certain
   93        you have the kernel option USERCONFIG set in your kernel, so
   94        that you can do a boot -c, to initially set your cards up.
   95        Then, edit /boot/loader.conf so that the following line
   96        shows up (overwriting, in effect, a similar line in
   97        /boot/default/loader.conf):
   98 
   99        userconfig_script_load="YES"
  100 
  101        My own pnp line looks like:
  102        pnp 1 0 os irq0 15 irq1 0 drq0 1 drq1 0 port0 1332
  103        (kget changes numbers from hexadecimal to decimal).  Note
  104        that, at this moment, the change from using /kernel.config
  105        to using /boot/kernel.conf as the storage place for kernel
  106        config changes is going on.  Take a look at your
  107        /boot/defaults/loader.conf, see what's defined as
  108        userconfig_script_name, and if you override, make sure the
  109        file exists.  Note that the loader only has access to the
  110        root filesystem, so be careful where you tell it to read
  111        from.
  112 
  113 
  114           o If you interrupt autoboot, you'll engage interactive
  115             mode with loader. Everything you type will have the
  116             same effects as if it were lines in /boot/loader.rc.
  117 
  118           o While in interactive mode, you can get help by typing
  119             "?", "help [<topic> [<subtopic>]]" and "help index".
  120             These are mostly commands one would expect a normal
  121             user to use. I recommend you play with them a little,
  122             to gain further familiarity with what's going on.
  123 
  124             Note that it is not possible to damage or corrupt your
  125             system while experimenting with the loader, as it
  126             cannot write to any of your filesystems.
  127 
  128           o The command "unload" will unload everything. This is
  129             very useful.  Once loader.rc has finished and the
  130             system is in the autoboot count-down, you will usually
  131             have the kernel and other modules loaded. Now, suppose
  132             your new /kernel is broken, how do you load
  133             /kernel.old? By typing:
  134 
  135                  unload
  136                  load kernel.old
  137                  [any other modules you wish to load]
  138                  boot
  139 
  140           o If you use loader.conf, you can do:
  141 
  142                  unload
  143                  set kernel=kernel.old
  144                  boot-conf
  145 
  146             this will then load all the modules you have
  147             configured, using kernel.old as kernel, and boot.
  148 
  149           o From loader, you can use the command "more" to read the
  150             contents of /boot/loader.rc, if you wish. This is not
  151             FreeBSD's more. It is one of loader's builtin commands.
  152             Useful if you can't quite recall what you have there.
  153             :-) Of course, you can use this command to read
  154             anything else you want.
  155 
  156           o "boot -flag" works, "boot kernelname" works, "boot
  157             -flag kernelname" doesn't. "boot kernelname -flag"
  158             might work, but I'm not sure. The problem is that these
  159             flags are kernel's flags, not boot's flags.
  160 
  161           o There are a number of variables that can be set. You
  162             can see them in loader.conf, but you can get much more
  163             detailed information using the "help" command, eg. help
  164             set <variablename>.
  165 
  166           o The variable root_disk_unit is particularly important,
  167             as it solves a relatively common problem. This problem
  168             shows when the BIOS assign disk units in a different
  169             way than the kernel. For example, if you have two IDE
  170             disks, one on the primary, the other on the secondary
  171             controller, and both as master, the default in most
  172             kernels is having the first as wd0, and the second as
  173             wd2. If your root partition is in wd2, you'll get an
  174             error, because the BIOS sees these disks as 0 and 1
  175             (well, 1 and 2), and that's what loader tells the
  176             kernel. In this case, "set root_disk_unit=2" solves the
  177             problem.  You use this whenever the kernel fails to
  178             mount to root partition because it has a wrong unit
  179             number.
  180 
  181        FILE OVERVIEW
  182 
  183 
  184           o /boot/defaults/loader.conf -- Master configuration
  185             file, not to be edited.  Overridden by
  186             /boot/loader.conf.
  187 
  188           o /boot/loader.conf -- local system customization file,
  189             in form very much like /boot/defaults/loader.conf.
  190             This file is meant to be used by local users and the
  191             sysinstall process.
  192 
  193           o /boot/loader.conf.local -- local installation override
  194             file.  This is intended for use by installations with
  195             large numbers of systems, to allow global policy
  196             overrides.  No FreeBSD tools should ever write this
  197             file.
  198 
  199           o /kernel.config -- old location of kernel configuration
  200             changes (like pnp changes).
  201 
  202           o /boot/kernel.conf -- new location for kernel
  203             configuration changes.
  204 
  205           o /boot/loader.rc -- loader initial configuration file,
  206             chiefly used to source in a forth file, and start the
  207             configuration process.
  208 
  209        NOTES ON LOADER.CONF SYNTAX
  210 
  211        I'm copy here from the last 11 lines from
  212        /boot/defaults/loader.conf:
  213 
  214        ##############################################################
  215        ###  Module loading syntax example  ##########################
  216        ##############################################################
  217 
  218        #module_load="YES"              # loads module "module"
  219        #module_name="realname"         # uses "realname" instead of "module"
  220        #module_type="type"             # passes "-t type" to load
  221        #module_flags="flags"           # passes "flags" to the module
  222        #module_before="cmd"            # executes "cmd" before loading module
  223        #module_after="cmd"             # executes "cmd" after loading module
  224        #module_error="cmd"             # executes "cmd" if load fails
  225 
  226        The way this works, the command processor used by the loader
  227        (which is a subset of forth) inspects  these  variables  for
  228        their  suffix,  and  the  7  lines  above illustrate all the
  229        currently defined suffixes, and their use.   Take  the  part
  230        before  the  underscore,  and customize it i(make it unique)
  231        for your particular use, keeping the  suffix  to  allow  the
  232        particular function you want to activate.  Extra underscores
  233        are fine, because it's only the  sufixes  that  are  scanned
  234        for.
  235 
  236 
  237 
  238        (authors Chuck Robey and Daniel Sobral).

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