8 .Nd building small FreeBSD disk images
12 .Op Ar config-name Op Ar site-name
16 utility is a script which produces a minimal implementation of
20 which typically fits on a small media such as a floppy disk,
21 or can be downloaded as a
22 single image file from some media such as CDROM, flash memory, or through
27 utility was originally created to build simple standalone systems
28 such as firewalls or bridges, but because of the ability to
29 cross-build images with different source trees than the one
30 in the server, it can be extremely useful to developers to
31 test their code without having to reinstall the system.
33 The boot media (historically a floppy disk, but also small
34 CDROM or USB keys) contains a boot loader and a
35 compressed kernel which includes a memory file system.
36 Depending on the media, it might also contain a number of
37 additional files, which can be updated at run time, and are
38 used to override/update those in the memory file system.
40 The system loads the kernel in the normal way, uncompresses
41 the memory file system and mounts it as root.
42 It then updates the memory
43 file system with files from the boot media (if present),
44 and executes a specialized version of
46 The boot media (floppy, etc.) is
47 required for loading only, and typically used read-only.
48 After the boot phase, the system runs entirely from RAM.
50 The following options are available (but also check the
52 script for more details).
53 The most important options for common operations are
59 .Bl -tag -width indent
62 Put the entire contents of the file system in the
63 memory file system image which is contained in the
65 This is the default behaviour, and is
66 extremely useful as the kernel itself can be loaded,
73 Clean the product of previous builds.
76 Specify a file that contains additional config commands.
78 .It Fl -floppy_size Ar size
79 Set the size of the disk image.
80 Typical values for a floppy disk are 1440 or 2880,
81 but other values can be used for other media (flash memories,
82 CDROM, network booted kernels).
83 Note that this option is overridden by the content of the
84 config files (config in the image tree, or the one
89 When used together with the
91 option, this initializes the
92 .Ao Ar SRC_PATH Ac Ns Pa /../usr
93 subtree as necessary to subsequently build
98 Generate an ISO image, picobsd.iso, in addition to the disk image picobsd.bin
101 Also build kernel modules.
102 These are not stored on the
104 image but are left available in the build directory.
107 Make the script non-interactive, skipping the initial menu
108 and proceeding with the build process without requiring user input.
110 .It Fl -no_all_in_mfs
111 Leaves files contained in the
115 image, so they can be loaded separately
116 from the kernel (and updated individually to
117 customize the image).
120 Omit /boot/loader, just rely on boot2 to load the kernel.
121 This saves some space but may have problems with kernels > 4MB.
123 .It Fl -objdir Ar directory
124 Specify a directory with the result of a previous buildworld.
125 This saves the need for an
127 call before creating an image.
129 .It Fl -src Ar SRC_PATH
130 Use the source tree at
134 This can be useful for cross-building
137 When using this option, you must also create and initialize the subtree at
138 .Ao Ar SRC_PATH Ac Ns Pa /../usr
139 with the correct header files, libraries, and tools (such as the
141 program) that are necessary for the cross-build (see the
144 The source files are unmodified by the
147 However the source tree is not completely read-only,
150 expects the kernel configuration file to be in one of
151 its subdirectories, and also the process of initializing the
153 subtree touches some parts of the source tree (this is a bug
154 in the release build scripts which might go away with time).
157 Make the script verbose, showing
158 commands to be executed and waiting for user
159 input before executing each of them.
160 Useful for debugging.
161 as a fully functional system.
164 As a result of extreme size limitations, the
166 environment differs from the normal
171 There are no dynamic libraries, and there is no directory
173 As a result, only static executables may be executed.
175 In order to reduce the size of the executables, all executables on a specific
176 floppy are joined together as a single executable built with
179 Some programs are supplied in minimalistic versions, specifically
181 a cut-down version of
185 a cut-down version of
191 sources reside in the hierarchy
192 .Pa /usr/src/release/picobsd .
193 In the following discussion, all relative path names are relative to this
196 The supported build script is
197 .Pa /usr/src/release/picobsd/build/picobsd
198 which can be run from anywhere, and relies on the
200 port to build a filesystem without requiring
202 or root privileges to mount a filesystem.
203 When run in interactive mode (the default without the
205 option), the script will let you configure the various parameters
206 used to build the PicoBSD image.
207 An image is configured
208 using the files and directories described below.
209 The base system contains a template, called
211 for historical reasons,
212 that can be used as a base for building various kinds
213 of network appliances.
215 You can define your own PicoBSD configuration, by creating a directory
216 with a name of your choice (e.g.\&
219 some of the following files and directories.
221 information on how to construct these files, look at one
224 configurations as a reference.
225 .Bl -tag -width indent
227 The kernel configuration file (required).
228 This is a mostly standard
229 kernel configuration file, possibly stripped down by removing
230 unnecessary drivers and options to reduce the kernel's size.
232 To be recognised as a
234 kernel config file, the file must also contain the line
237 below, and a matching
240 .Bd -literal -offset indent
241 #marker def_sz init MFS_inodes floppy_inodes
242 #PicoBSD 4200 init 8192 32768
243 options MD_ROOT_SIZE=4200 # same as def_sz
246 This informs the script of the size of the memory file system and
247 provides a few other details on how to build the image.
250 configuration (required).
251 It contains the list of directories containing program sources,
252 the list of binaries to be built, and the list of libraries that
256 manpage for the exact details on the syntax of this file.
258 The following issues are particularly important when dealing
264 We can pass build options to those makefiles which understand
265 that, in order to reduce the size of the programs.
266 This is achieved with a line of the form
268 .Dl "buildopts -DNO_PAM -DRELEASE_CRUNCH ..."
270 When providing the list of directories where source files are, it
271 is convenient to list the following entry first:
273 .Dl "srcdirs /usr/src/release/picobsd/tinyware"
277 versions of the programs will be found there.
281 is replaced with the full pathname of the directory where the
283 configuration resides (i.e., the one where we find
284 .Pa PICOBSD , crunch.conf ,
286 This can be useful to refer source code that resides within a
287 configuration, e.g.\&
289 .Dl "srcdirs @__CWD__@/src"
292 Shell variables, sourced by the
295 The most important variables here are:
296 .Bl -tag -width ".Va MY_DEVS"
302 Should be set to the list of devices to be created in the
304 directory of the image (it is really the argument passed to
306 so refer to that manpage for the names).
308 Size (in kilobytes) of the
314 which produces an image suitable for a standard floppy.
316 If you plan to store the image on a CDROM (e.g.\& using
319 floppy emulation), you can set
322 If you are planning to dump the image onto a hard disk
323 (either in a partition or on the whole disk), you
324 are not restricted to one of the standard floppy sizes.
325 Using a large image size per se does not waste RAM at runtime,
326 because only the files that are actually loaded from the image
327 contribute to the memory usage.
329 Contains a list of files to be imported in the floppy tree.
330 Absolute names refer to the standard file system, relative
331 names refer to the root of the source tree being used
334 You can normally use this option if you want to import
335 files such as shared libraries, or databases, without
336 having to replicate them first in your configuration
341 .It Pa floppy.tree.exclude
342 List of files from the standard floppy tree which
343 we do not want to be copied (optional).
345 Local additions to the standard floppy tree (optional).
346 The content of this subtree will be copied as-is into the
348 .It Pa floppy.tree. Ns Aq Ar site-name
349 Same as above, but site-specific (optional).
352 More information on the build process can be found in the
356 .Sh USING ALTERNATE SOURCE TREES
357 The build script can be instructed to use an alternate source tree
361 The tree that you specify must contain full sources for the kernel
362 and for all programs that you want to include in your image.
363 As an example, to cross-build the
366 using RELENG_4 sources, you can do the following:
367 .Bd -literal -offset indent
368 cd <some_empty_directory>
370 (cd FOO; cvs -d<my_repository> co -rRELENG_4 src)
371 picobsd --src FOO/src --init # this is needed only once
372 picobsd --src FOO/src -n -v bridge
375 If the build is successful, the directory
376 .Pa build_dir-bridge/
379 that can be downloaded with
381 a floppy image called
383 plus the products of the compilation in other directories.
384 If you want to modify the source tree in
386 a new image can be produced by simply running
388 .Dl "picobsd --src FOO/src -n -v bridge"
390 whereas if the change affects include files or libraries
391 you first need to update them, e.g.\& by re-running
393 .Dl "picobsd --src FOO/src --init # this is needed only once"
395 as you would normally do for any change of this kind.
396 .Sh INSTALLING PicoBSD
400 is run from a floppy disk, where it can be installed with a simple
402 .Dl "dd if=picobsd.bin of=/dev/rfd0"
404 and the floppy is ready to boot.
405 .Ss Hard Disk Install
406 The same process can be used to store the image on a hard disk
407 (entire volume or one of the slices):
408 .Bd -literal -offset indent
409 dd if=picobsd.bin of=/dev/ad2
410 dd if=picobsd.bin of=/dev/ad2s3
411 dd if=picobsd.bin of=/dev/ad2 oseek=NN
414 The first form will install the image on the entire disk, and it
415 should work in the same way as for a floppy.
417 The second form will install the image
418 on slice number 3 (which should be large enough to store the
419 contents of the image).
420 However, the process will only have success if the
421 partition does not contain a valid disklabel, otherwise the kernel will
422 likely prevent overwriting the label.
423 In this case you can use the
424 third form, replacing
426 with the actual start of the partition
427 (which you can determine using
429 Note that after saving the image to the slice, it will not yet be
433 command to properly initialize the label (do not ask why!).
434 One way to do this is
435 .Bd -literal -offset indent
436 disklabel -w ad0s2 auto
440 and from the editor enter a line corresponding to the actual partition, e.g.\&
441 if the image has 2.88MB (5760 sectors) you need to enter the following
442 line for the partition:
444 .Dl "a: 5760 0 4.2BSD 512 4096"
446 At this point the partition is bootable.
447 Note that the image size can be smaller than the slice size
448 (indicated as partition
452 can produce an ISO image named picobsd.iso,
455 emulation, so it has no size restrictions.
456 Installing means just burning a media with the file.
457 .Ss Booting From The Network
458 Yet another way to use
460 is to boot the image off the network.
461 For this purpose you should use the uncompressed kernel which is
462 available as a byproduct of the compilation.
463 Refer to the documentation
464 for network booting for more details, the
466 kernel is bootable as a standard
472 insert the floppy and reset the machine.
473 The boot procedure is similar to the
477 Booting from a floppy is normally rather slow (in the order of 1-2
478 minutes), things are much faster if you store your image on
479 a hard disk, Compact Flash, or CDROM.
483 to load the preloaded, uncompressed kernel image
484 which is a byproduct of the
488 the load time is a matter of a few seconds, even on a 10Mbit/s
493 loads the root file system from the memory file system, starts
495 and passes control to a first startup script,
497 The latter populates the
501 directories with the default files, then tries to identify the boot
502 device (floppy, hard disk partition) and possibly override the contents
503 of the root file system with files read from the boot device.
504 This allows you to store local configuration on the same media.
505 After this phase the boot device is no longer used, unless the
506 user specifically does it.
508 After this, control is transferred to a second script,
510 (which can be overridden from the boot device).
511 This script tries to associate a hostname to the system by using
512 the MAC address of the first ethernet interface as a key, and
515 Then control is passed to the main user configuration script,
517 which is supposed to override the value of a number of configuration
518 variables which have been pre-set in
519 .Pa /etc/rc.conf.defaults .
522 variable to create different configurations from the same file.
523 After taking control back,
525 completes the initializations, and as part of this
526 it configures network interfaces and optionally calls the
527 firewall configuration script,
528 .Pa /etc/rc.firewall ,
529 where the user can store his own firewall configuration.
533 runs entirely from main memory, and has no swap space, unless you
534 explicitly request it.
535 The boot device is also not used anymore after
537 takes control, again, unless you explicitly request it.
538 .Sh CONFIGURING a PicoBSD system
541 system can be configured through a few files which are read at boot
542 time, very much like a standard
545 There are, however, some minor differences to reduce the
546 number of files to store and/or customize, thus saving space.
547 Among the files to configure we have the following:
548 .Bl -tag -width indent
550 Traditionally, this file contains the IP-to-hostname mappings.
551 In addition to this, the
553 version of this file also contains
554 a mapping between Ethernet (MAC) addresses and hostnames, as follows:
555 .Bd -literal -offset indent
556 #ethertable start of the ethernet->hostname mapping
557 # mac_address hostname
558 # 00:12:34:56:78:9a pinco
563 where the line containing
565 marks the start of the table.
567 If the MAC address is not found, the script will prompt you to
568 enter a hostname and IP address for the system, and this
569 information will be stored in the
571 file (in memory) so you can simply store them on disk later.
573 Note that you can use wildcards in the address part, so a line
574 like the last one in the example will match any MAC address and
577 This file contains a number of variables which control the
578 operation of the system, such as interface configuration,
579 router setup, network service startup, etc.
580 For the exact list and meaning of these variables see
581 .Pa /etc/rc.conf.defaults .
583 It is worth mentioning that some of the variables let you
584 overwrite the contents of some files in
586 This option is available at the moment for
589 .Pa /etc/resolv.conf ,
590 whose contents are generally very short and suitable for this
592 In case you use these variables, remember to use newlines
593 as appropriate, e.g.\&
594 .Bd -literal -offset indent
595 host_conf="# this goes into /etc/host.conf
600 Although not mandatory, in this file you should only set the
601 variables indicated in
602 .Pa /etc/rc.conf.defaults ,
603 and avoid starting services which depend on having the network running.
604 This can be done at a later time: if you set
605 .Va firewall_enable Ns = Ns Qq Li YES ,
608 script will be run after configuring the network interfaces,
609 so you can set up your firewall and safely start network services or enable
610 things such as routing and bridging.
611 .It Pa /etc/rc.firewall
612 This script can be used to configure the
617 variable is set to the pathname of the firewall command,
619 contains the value set in
623 contains the name assigned to the host.
626 There is a small script called
628 which can be used to edit and/or save to disk a copy of the files
629 you have modified after booting.
630 The script takes one or more absolute pathnames, runs the
631 editor on the files passed as arguments, and then saves a
632 compressed copy of the files on the disk (mounting and
633 unmounting the latter around the operation).
635 If invoked without arguments,
638 .Pa rc.conf , rc.firewall ,
642 If one of the arguments is
644 (the directory name alone),
645 then the command saves to disk (without editing)
646 all the files in the directory for which a copy
647 already exists on disk (e.g.\& as a result of a previous update).
654 .An Andrzej Bialecki Aq abial@FreeBSD.org ,
655 with subsequent work on the scripts by
656 .An Luigi Rizzo Aq luigi@iet.unipi.it
661 .An Greg Lehey Aq grog@lemis.com .
663 Documentation is still incomplete.