1<html><head><title>toybox FAQ</title>
   2<!--#include file="header.html" -->
   4<h1>Frequently Asked Questions</h1>
   6<h2>General Questions</h2>
   9<li><h2><a href="#why_toybox">Why toybox? (What was wrong with busybox?)</a></h2></li>
  10<li><h2><a href="#capitalize">Do you capitalize toybox?</a></h2></li>
  11<li><h2><a href="#support_horizon">Why a 7 year support horizon?</a></h2></li>
  12<li><h2><a href="#releases">Why time based releases?</a></h2></li>
  13<li><h2><a href="#code">Where do I start understanding the toybox source code?</a></h2></li>
  14<li><h2><a href="#when">When were historical toybox versions released?</a></h2></li>
  15<li><h2><a href="#bugs">Where do I report bugs?</a></h2></li>
  16<li><h2><a href="#b_links">What are those /b/number links in the git log?</a></h2></li>
  17<li><h2><a href="#opensource">What is the relationship between toybox and android?</a></h2></li>
  18<li><h2><a href="#backporting">Will you backport fixes to old versions?</a></h2></li>
  19<li><h2><a href="#dotslash">What's this ./ on the front of commands in your examples?</a></h2></li>
  23<h2>Using toybox</h2>
  26<!-- get binaries -->
  27<li><h2><a href="#install">How do I install toybox?</h2></li>
  28<li><h2><a href="#cross">How do I cross compile toybox?</h2></li>
  29<li><h2><a href="#system">What part of Linux/Android does toybox provide?</h2></li>
  30<li><h2><a href="#mkroot">How do I build a working Linux system with toybox?</a></h2></li>
  33<hr /><h2><a name="why_toybox" />Q: "Why is there toybox? What was wrong with busybox?"</h2>
  35<p>A: Toybox started back in 2006 when I (Rob Landley)
  36<a href=>handed off BusyBox maintainership</a>
  37and <a href=>started over from
  38scratch</a> on a new codebase after a
  39<a href=>protracted licensing argument</a> took all the fun out of working on BusyBox.</p>
  41<p>Toybox was just a personal project until it got
  42<a href=>relaunched</a>
  43in November 2011 with a new goal to make Android
  44<a href=>self-hosting</a>.
  45This involved me relicensing my own
  46code, which made people who had never used or participated in the project
  47<a href=>loudly angry</a>. The switch came
  48after a lot of thinking <a href=>about
  49licenses</a> and <a href=>the
  50transition to smartphones</a>, which led to a
  51<a href=>2013 talk</a> laying
  52out a
  53<a href=>strategy</a>
  54to make Android self-hosting using toybox. This helped
  55<a href=>bring
  56it to Android's attention</a>, and they
  57<a href=>merged it</a> into Android M.</p>
  59<p>The unfixable problem with busybox was licensing: BusyBox predates Android
  60by almost a decade, but Android still doesn't ship with it because GPLv3 came
  61out around the same time Android did and caused many people to throw
  62out the GPLv2 baby with the GPLv3 bathwater.
  63Android <a href=>explicitly
  64discourages</a> use of GPL and LGPL licenses in its products, and has gradually
  65reimplemented historical GPL components (such as its bluetooth stack) under the
  66Apache license. Apple's
  67<a href=>less subtle</a> response was to freeze xcode at the last GPLv2 releases
  68(GCC 4.2.1 with binutils 2.17) for over 5 years while sponsoring the
  69development of new projects (clang/llvm/lld) to replace them,
  70implementing a
  71<a href=>new SMB server</a> from scratch to
  72<a href=>replace samba</a>,
  73switching <a href=>bash with zsh</a>, and so on.
  74Toybox itself exists because somebody with in a legacy position
  75just wouldn't shut up about GPLv3, otherwise I would probably
  76still happily be maintaining BusyBox. (For more on how I wound
  77up working on busybox in the first place,
  78<a href=>see here</a>.)</p>
  80<hr /><h2><a name="capitalize" />Q: Do you capitalize toybox?</h2>
  82<p>A: Only at the start of a sentence. The command name is all lower case so
  83it seems silly to capitalize the project name, but not capitalizing the
  84start of sentences is awkward, so... compromise. (It is _not_ "ToyBox".)</p>
  86<hr /><h2><a name="support_horizon">Q: Why a 7 year support horizon?</a></h2>
  88<p>A: Our <a href=>longstanding rule of thumb</a> is to try to run and build on
  89hardware and distributions released up to 7 years ago, and feel ok dropping
  90support for stuff older than that. (This is a little longer than Ubuntu's
  91Long Term Support, but not by much.)</p>
  93<p>My original theory was "4 to 5 of the 18-month cycles of moore's law should cover
  94the vast majority of the installed base of PC hardware", loosely based on some
  95research I did <a href=>back in 2003</a>
  96and <a href=>updated in 2006</a>
  97which said that low end systems were 2 iterations of moore's
  98law below the high end systems, and that another 2-3 iterations should cover
  99the useful lifetime of most systems no longer being sold but still in use and
 100potentially being upgraded to new software releases.</p>
 102<p>That analysis missed <a href=>industry
 103changes</a> in the 1990's that stretched the gap
 104from low end to high end from 2 cycles to 4 cycles, and ignored
 105<a href=>the switch</a> from PC to smartphone cutting off the R&D air supply of the
 106laptop market. Meanwhile the Moore's Law <a href=>s-curve</a> started bending back down (as they
 107<a href=>always do</a>)
 108back in 2000, and these days is pretty flat: the drive for faster clock
 109speeds <a href=>stumbled</a>
 110and <a href=>died</a>, with
 111the subsequent drive to go "wide" maxing out for most applications
 112around 4x SMP with maybe 2 megabyte caches. These days the switch from exponential to
 113linear growth in hardware capabilities is
 114<a href=>common knowledge</a> and
 115<a href=>widely
 118<p>But the 7 year rule of thumb stuck around anyway: if a kernel or libc
 119feature is less than 7 years old, I try to have a build-time configure test
 120for it to let the functionality cleanly drop out. I also keep old Ubuntu
 121images around in VMs to perform the occasional defconfig build there to
 122see what breaks. (I'm not perfect about this, but I accept bug reports.)</p>
 124<hr /><h2><a name="releases" />Q: Why time based releases?</h2>
 125<p>A: Toybox targets quarterly releases (a similar schedule to the Linux
 126kernel) because Martin Michlmayr's excellent
 127<a href=>talk on the
 128subject</a> was convincing. This is actually two questions, "why have
 129releases" and "why schedule them".</p>
 131<p>Releases provide synchronization points where the developers certify
 132"it worked for me". Each release is a known version with predictable behavior,
 133and right or wrong at least everyone should be seeing
 134similar results so might be able to google an unexpected outcome.
 135Releases focus end-user testing on specific versions
 136where issues can be reproduced, diagnosed, and fixed.
 137Releases also force the developers to do periodic tidying, packaging,
 138documentation review, finish up partially implemented features languishing
 139in their private trees, and give regular checkpoints to measure progress.</p>
 141<p>Changes accumulate over time: different feature sets, data formats,
 142control knobs... Toybox's switch from "ls -q" to "ls -b" as the default output
 143format was not-a-bug-it's-a "design improvement", but the
 144difference is academic if the change breaks somebody's script.
 145Releases give you the option to schedule upgrades as maintenance, not to rock
 146the boat just now, and use a known working release version until later.</p>
 148<p>The counter-argument is that "continuous integration"
 149can be made robust with sufficient automated testing. But like the
 150<a href=>waterfall method</a>, this places insufficent
 151emphasis on end-user feedback and learning from real world experience.
 152Developer testing is either testing that the code does what the developers
 153expect given known inputs running in an established environment, or it's
 154regression testing against bugs previously found in the field. No plan
 155survives contact with the enemy, and technology always breaks once it
 156leaves the lab and encounters real world data and use cases in new
 157runtime and build environments.</p>
 159<p>The best way to give new users a reasonable first experience is to point
 160them at specific stable versions where development quiesced and
 161extra testing occurred. There will still be teething troubles, but multiple
 162people experiencing the _same_ teething troubles can potentially
 163help each other out.</p>
 165<p>Releases on a schedule are better than releases "when it's ready" for
 166the same reason a regularly scheduled bus beats one that leaves when it's
 167"full enough": the schedule lets its users make plans. Even if the bus leaves
 168empty you know when the next one arrives so missing this one isn't a disaster.
 169and starting the engine to leave doesn't provoke a last-minute rush of nearby
 170not-quite-ready passengers racing to catch it causing further delay and
 171repeated start/stop cycles as it ALMOST leaves.
 172(The video in the first paragraph goes into much greater detail.)</p>
 174<hr /><h2><a name="code" />Q: Where do I start understanding the source code?</h2>
 176<p>A: Toybox is written in C. There are longer writeups of the
 177<a href=design.html>design ideas</a> and a <a href=code.html>code walkthrough</a>,
 178and the <a href=about.html>about page</a> summarizes what we're trying to
 179accomplish, but here's a quick start:</p>
 181<p>Toybox uses the standard three stage configure/make/install
 182<a href=code.html#building>build</a>, in this case "<b>make defconfig;
 183make; make install</b>". Type "<b>make help</b>" to
 184see available make targets.</p>
 186<p><u>The configure stage</u> is copied from the Linux kernel (in the "kconfig"
 187directory), and saves your selections in the file ".config" at the top
 188level. The "<b>make defconfig</b>" target selects the
 189maximum sane configuration (enabling all the commands and features that
 190aren't unfinished, or only intended as examples, or debug code...) and is
 191probably what you want. You can use "<b>make menuconfig</b>" to manually select
 192specific commands to include, through an interactive menu (cursor up and
 193down, enter to descend into a sub-menu, space to select an entry, ? to see
 194an entry's help text, esc to exit). The menuconfig help text is the
 195same as the command's "<b>--help</b>" output.</p>
 197<p><u>The "make" stage</u> creates a toybox binary (which is stripped, look in
 198generated/unstripped for the debug versions), and "<b>make install</b>" adds a bunch of
 199symlinks to toybox under the various command names. Toybox determines which
 200command to run based on the filename, or you can use the "toybox" name in which case the first
 201argument is the command to run (ala "toybox ls -l").</p>
 203<p><u>You can also build
 204individual commands as standalone executables</u>, ala "make sed cat ls".
 205The "make change" target builds all of them, as in "change for a $20".</p>
 207<p><u>The main() function is in main.c</u> at the top level,
 208along with setup plumbing and selecting which command to run this time.
 209The function toybox_main() in the same file implements the "toybox"
 210multiplexer command that lists and selects the other commands.</p>
 212<p><u>The individual command implementations are under "toys"</u>, and are grouped
 213into categories (mostly based on which standard they come from, posix, lsb,
 214android...) The "pending" directory contains unfinished commands, and the
 215"examples" directory contains example code that aren't really useful commands.
 216Commands in those two directories
 217are _not_ selected by defconfig. (Most of the files in the pending directory
 218are third party submissions that have not yet undergone
 219<a href=cleanup.html>proper code review</a>.)</p>
 221<p><u>Common infrastructure shared between commands is under "lib"</u>. Most
 222commands call lib/args.c to parse their command line arguments before calling
 223the command's own main() function, which uses the option string in
 224the command's NEWTOY() macro. This is similar to the libc function getopt(),
 225but more powerful, and is documented at the top of lib/args.c. A NULL option
 226string prevents this code from being called for that command.</p>
 228<p><u>The build/install infrastructure is shell scripts under
 229"scripts"</u> (starting with scripts/ and scripts/
 230<u>These populate the "generated" directory</u> with headers
 231created from other files, which are <a href=code.html#generated>described</a>
 232in the code walkthrough. All the
 233build's temporary files live under generated, including the .o files built
 234from the .c files (in generated/obj). The "make clean" target deletes that
 235directory. ("make distclean" also deletes your .config and deletes the
 236kconfig binaries that process .config.)</p>
 238<p><u>Each command's .c file contains all the information for that command</u>, so
 239adding a command to toybox means adding a single file under "toys".
 240Usually you <a href=code.html#adding>start a new command</a> by copying an
 241existing command file to a new filename
 242(toys/examples/hello.c, toys/examples/skeleton.c, toys/posix/cat.c,
 243and toys/posix/true.c have all been used for this purpose) and then replacing
 244all instances of its old name with the new name (which should match the
 245new filename), and modifying the help text, argument string, and what the
 246code does. You might have to "make distclean" before your new command
 247shows up in defconfig or menuconfig.</p>
 249<p><u>The toybox test suite lives in the "tests" directory</u>, and is
 250driven by scripts/ and scripts/ From the top
 251level you can "make tests" to test everything, or "make test_sed" to test a
 252single command's standalone version (which should behave identically,
 253but that's why we test). You can set TEST_HOST=1 to test the host version
 254instead of the toybox version (in theory they should work the same),
 255and VERBOSE=all to see diffs of the expected and actual output for all
 256failing tests. The default VERBOSE=fail stops at the first such failure.</p>
 258<hr /><h2><a name="when" />Q: When were historical toybox versions released?</h2>
 260<p>A: For vanilla releases, check the
 261<a href=>date on the commit tag</a>
 262or <a href=>the
 263example binaries</a> against the output of "toybox --version".
 264Between releases the --version
 265information is in "git describe --tags" format with "tag-count-hash" showing the
 266most recent commit tag, the number of commits since that tag, and
 267the hash of the current commit.</p>
 269<p>Android makes its own releases on its own
 270<a href=>schedule</a>
 271using its own version tags, but lists corresponding upstream toybox release
 272versions <a href=>here</a>. For more detail you can look up
 273<a href=>AOSP's
 274git tags</a>. (The <a href=>Android Open Source Project</a> is the "upstream" android vendors
 275start form when making their own releases. Google's phones run AOSP versions
 276verbatim, other vendors tend to take those releases as starting points to
 279<p>If you want to find the vanilla toybox commit corresponding to an AOSP
 280toybox version, find the most recent commit in the android log that isn't from a
 281@google or @android address and search for it in the vanilla commit log.
 282(The timestamp should match but the hash will differ,
 283because each git hash includes the previous
 284git hash in the data used to generate it so all later commits have a different
 285hash if any of the tree's history differs; yes Linus Torvalds published 3 years
 286before Satoshi Nakamoto.) Once you've identified the vanilla commit's hash,
 287"git describe --tags $HASH" in the vanilla tree should give you the --version
 288info for that one.</p>
 290<hr /><h2><a name="bugs" />Q: Where do I report bugs?</h2>
 292<p>A: Ideally on the <a href=>mailing list</a>, although <a>emailing the
 293maintainer</a> is a popular if slightly less reliable alternative.
 294Issues submitted to <a href=>github</a>
 295are generally dealt with less promptly, but mostly get done eventually.
 296AOSP has its <a href=>own bug reporting mechanism</a> (although for toybox they usually forward them
 297to the mailing list) and Android vendors usually forward them to AOSP which
 298forwards them to the list.</p>
 300<p>Note that if we can't reproduce a bug, we probably can't fix it.
 301Not only does this mean providing enough information for us to see the
 302behavior ourselves, but ideally doing so in a reasonably current version.
 303The older it is the greater the chance somebody else found and fixed it
 304already, so the more out of date the version you're reporting a bug against
 305the less effort we're going to put into reproducing the problem.</p>
 307<hr /><h2><a name="b_links" />Q: What are those /b/number bug report
 308links in the git log?</h2>
 310<p>A: It's a Google thing. Replace /b/$NUMBER with
 311$NUMBER to read it outside the googleplex.</p>
 313<hr /><a name="opensource" /><h2>Q: What is the relationship between toybox and android?</h2>
 315<p>A: The <a href=about.html>about page</a> tries to explain that,
 316and Linux Weekly News has covered toybox's history a
 317<a href=>little</a>
 318<a href=>over</a>
 319<a href=>the</a>
 320<a href=>years</a>.</p>
 322<p>Toybox is a traditional open source project created and maintained
 323by hobbyist (volunteer) developers, originally for Linux but these days
 324also running on Android, BSD, and MacOS. The project started in 2006
 325and its original author (Rob Landley)
 326continues to maintain the open source project.</p>
 328<p>Android's base OS maintainer (Elliott Hughes, I.E. enh)
 329<a href=>ported</a>
 330<a href=>toybox</a>
 331to Android in 2014, merged it into Android M (Marshmallow), and remains
 332Android's toybox maintainer. (He explained it in his own words in
 333<a href=>this podcast</a>, starting either 18 or 20 minutes in depending how
 334much backstory you want.)</p>
 336<p>Android's policy for toybox development is to push patches to the
 337open source project (submitting them via the mailing list) then
 338"git pull" the public tree into Android's tree. To avoid merge conflicts, Android's
 339tree doesn't change any of the existing toybox files but instead adds <a href=>parallel
 340build infrastructure</a> off to one side. (Toybox uses a make wrapper around bash
 341scripts, AOSP builds with soong/ninja instead and checks in a snapshot of the
 342generated/ directory to avoid running kconfig each build).
 343Android's changes to toybox going into the open source tree first
 344and being pulled from there into Android keeps the two trees in
 345sync, and makes sure each change undergoes full open source design review
 346and discussion.</p>
 348<p>Rob acknowledges Android is by far the largest userbase for the project,
 349but develops on a standard 64-bit Linux+glibc distro while building embedded
 35032-bit big-endian nommu musl systems requiring proper data alignment for work,
 351and is not a Google employee so does not have access
 352to the Google build cluster of powerful machines capable of running the full
 353AOSP build in a reasonable amount of time. Rob is working to get android
 354building under android (the list of
 355toybox tools Android's build uses is
 356<a href=>here</a>,
 357and what else it needs from its build environment is
 358<a href=>here</a>), and he hopes someday to not only make a usable development
 359environment out of it but also nudge the base OS towards a more granular
 360package management system allowing you to upgrade things like toybox without
 361a complete reinstall and reboot, plus the introduction of a "posix container"
 362within which you can not only run builds, but selinux lets you run binaries
 363you've just built). In the meantime, Rob tests static bionic
 364builds via the Android NDK when he remembers, but has limited time to work
 365on toybox because it's not his day job. (The products his company makes ship
 366toybox and they do sponsor the project's development, but it's one of many
 367responsibilities at work.)</p>
 369<p>Elliott is the Android base OS maintainer, in which role he manages
 370a team of engineers. He also has limited time for toybox, both because it's one
 371of many packages he's responsible for (he maintains bionic, used to maintain
 372dalvik...) and because he allowed himself to be promoted into management
 373and thus spends less time coding than he does sitting in meetings where testers
 374talk to security people about vendor issues.</p>
 376<p>Android has many other coders and security people who submit the occasional
 377toybox patch, but of the last 1000 commits at the <a href=>time
 378of writing</a> this FAQ entry, Elliott submitted 276 and all other
 379or addresses combined totaled 17. (Rob submitted 591, leaving
 380116 from other sources, but for both Rob and Elliott there's a lot of "somebody
 381else pointed out an issue, and then we wrote a patch". A lot of patches
 382from both "Author:" lines thank someone else for the suggestion in the
 383commit comment.)</p>
 385<hr /><a name="backporting" /><h2>Q: Will you backport fixes to old versions?</h2>
 387<p>A: Probably not. The easiest thing to do is get your issue fixed upstream
 388in the current release, then get the newest version of the
 389project built and running in the old environment.</p>
 391<p>Backporting fixes generally isn't something open source projects run by
 392volunteer developers do because the goal of the project's development community
 393is to extend and improve the project. We're happy to respond to our users'
 394needs, but if you're coming to the us for free tech support we're going
 395to ask you to upgrade to a current version before we try to diagnose your
 398<p>The volunteers are happy to fix any bugs you point out in the current
 399versions because doing so helps everybody and makes the project better. We
 400want to make the current version work for you. But diagnosing, debugging, and
 401backporting fixes to old versions doesn't help anybody but you, so isn't
 402something we do for free. The cost of volunteer tech support is using a
 403reasonably current version of the project.</p>
 405<p>If you're using an old version built with an old
 406compiler on an old OS (kernel and libc), there's a fairly large chance
 407whatever problem you're
 408seeing already got fixed, and to get that fix all you have to do is upgrade
 409to a newer version. Diagnosing a problem that wasn't our bug means we spent
 410time that only helps you, without improving the project.
 411If you don't at least _try_ a current version, you're asking us for free
 412personalized tech support.</p>
 414<p>Reproducing bugs in current versions also makes our job easier.
 415The further back in time
 416you are, the more work it is for us digging back in the history to figure
 417out what we hadn't done yet in your version. If spot a problem in a git
 418build pulled 3 days ago, it's obvious what changed and easy to fix or back out.
 419If you ask about the current release version 3 months after it came out,
 420we may have to think a while to remember what we did and there are a number of
 421possible culprits, but it's still tractable. If you ask about 3 year old
 422code, we have to reconstruct the history and the problem could be anything,
 423there's a lot more ground to cover and we haven't seen it in a while.</p>
 425<p>As a rule of thumb, volunteers will generally answer polite questions about
 426a given version for about three years after its release before it's so old
 427we don't remember the answer off the top of our head. And if you want us to
 428put any _effort_ into tracking it down, we want you to put in a little effort
 429of your own by confirming it's still a problem with the current version
 430(I.E. we didn't fix it already). It's
 431also hard for us to fix a problem of yours if we can't reproduce it because
 432we don't have any systems running an environment that old.</p>
 434<p>If you don't want to upgrade, you have the complete source code and thus
 435the ability to fix it yourself, or can hire a consultant to do it for you. If
 436you got your version from a vendor who still supports the older version, they
 437can help you. But there are limits as to what volunteers will feel obliged to
 438do for you.</p>
 440<p>Commercial companies have different incentives. Your OS vendor, or
 441hardware vendor for preinstalled systems, may have their own bug reporting
 442mechanism and update channel providing backported fixes. And a paid consultant
 443will happily set up a special environment just to reproduce your problem.</p>
 445<hr /><h2><a name="install" />Q: How do I install toybox?</h2>
 448Multicall binaries like toybox behave differently based on the filename
 449used to call them, so if you "mv toybox ls; ./ls -l" it acts like ls. Creating
 450symlinks or hardlinks and adding them to the $PATH lets you run the
 451commands normally by name, so that's probably what you want to do.</p>
 453<p>If you already have a <a href=>toybox binary</a>
 454you can install a tree of command symlinks to
 455<a href=>the
 456standard path</a>
 457locations (<b>export PATH=/bin:/usr/bin:/sbin:/usr/sbin</b>) by doing:</p>
 459<blockquote><p><b>for i in $(/bin/toybox --long); do ln -s /bin/toybox $i; done</b></p></blockquote>
 461<p>Or you can install all the symlinks in the same directory as the toybox binary
 462(<b>export PATH="$PWD:$PATH"</b>) via:</p>
 464<blockquote><p><b>for i in $(./toybox); do ln -s toybox $i; done</b></p></blockquote></p>
 466<p>When building from source, use the "<b>make install</b>" and
 467"<b>make install_flat</b>"
 468targets with an appropriate <b>PREFIX=/target/path</b> either
 469exported or on the make command line. When cross compiling,
 470"<b>make list</b>" outputs the command names enabled by defconfig.
 471For more information, see "<b>make help</b>".</p>
 473<p>The command name "toybox" takes the second argument as the name of the
 474command to run, so "./toybox ls -l" also behaves like ls. The "toybox"
 475name is special in that it can have a suffix (toybox-i686 or toybox-1.2.3)
 476and still be recognized, so you can have multiple versions of toybox in the
 477same directory.</p>
 479<p>When toybox doesn't recognize its
 480filename as a command, it dereferences one
 481level of symlink. So if your script needs "gsed" you can "ln -s sed gsed",
 482then when you run "gsed" toybox knows how to be "sed".</p>
 484<hr /><h2><a name="dotslash" />Q: What's this ./ on the front of commands in your examples?</h2>
 486<p>A: When you don't give a path to a command's executable file,
 487linux command shells search the directories listed in the $PATH envionment
 488variable (in order), which usually doesn't include the current directory
 489for security reasons. The
 490magic name "." indicates the current directory (the same way ".." means
 491the parent directory and starting with "/" means the root directory)
 492so "./file" gives a path to the executable file, and thus runs a command
 493out of the current directory where just typing "file" won't find it.
 494For historical reasons PATH is colon-separated, and treats an
 495empty entry (including leading/trailing colon) as "check the current
 496directory", so if you WANT to add the current directory to PATH you
 497can PATH="$PATH:" but doing so is a TERRIBLE idea.</p>
 499<p>Toybox's shell (toysh) checks for built-in commands before looking at the
 500$PATH (using the standard "bash builtin" logic just with lots more builtins),
 501so "ls" doesn't have to exist in your filesystem for toybox to find it. When
 502you give a path to a command the shell won't run the built-in version
 503but will run the file at that location. (But the multiplexer command
 504won't: "toybox /bin/ls" runs the built-in ls, you can't point it at an
 505arbitrary file out of the filesystem and have it run that. You could
 506"toybox nice /bin/ls" though.)</p>
 508<hr /><h2><a name="standalone" />Q: How do I make individual/standalone toybox command binaries?</h2>
 510<p>After running the configure step (generally "make defconfig")
 511you can "make list" to see available command names you can use as build
 512targets to build just that command
 513(ala "make sed"). Commands built this way do not contain a multiplexer and
 514don't care what the command filename is.</p>
 516<p>The "make change" target (as in change for a $20) builds every command
 517standalone (in the "change" subdirectory). Note that this is collectively
 518about 10 times as large as the multiplexer version, both in disk space and
 519runtime memory. (Even more when statically linked.)</p>
 521<hr /><h2><a name="cross" />Q: How do I cross compile toybox?</h2>
 523<p>A: You need a compiler "toolchain" capable of producing binaries that
 524run on your target. A toolchain is an
 525integrated suite of compiler, assembler, and linker, plus the standard
 526headers and
 527libraries necessary to build C programs. (And a few miscellaneous binaries like
 528nm and objdump.)</p>
 530<p>Toybox is tested against two compilers (llvm, gcc) and three C libraries
 531(bionic, musl, glibc) in the following combinations:</p>
 533<a name="cross1" />
 534<p><a href="#cross1">1) gcc+glibc = host toolchain</a></p>
 536<p>Most Linux distros come with that as a host compiler, which is used by
 537default when you build normally
 538(<b>make distclean defconfig toybox</b>, or <b>make menuconfig</b> followed
 539by <b>make</b>).</p>
 541<p>You can use LDFLAGS=--static if you want static binaries, but static
 542glibc is hugely inefficient ("hello world" is 810k on x86-64) and throws a
 543zillion linker warnings because one of its previous maintainers
 544<a href=>was insane</a>
 545(which meant at the time he refused to fix
 546<a href=>obvious bugs</a>), plus it uses dlopen() at runtime to implement basic things like
 547<a href=>DNS lookup</a> (which is almost impossible
 548to support properly from a static binary because you wind up with two
 549instances of malloc() managing two heaps which corrupt as soon as a malloc()
 550from one is free()d into the other, although glibc added
 551<a href=>improper support</a> which still requires the shared libraries to be
 552installed on the system alongside the static binary:
 553<a href=>in brief, avoid</a>).
 554These days glibc is <a href=>maintained
 555by a committee</a> instead of a single
 556maintainer, if that's an improvement. (As with Windows and
 557Cobol, most people deal with it and get on with their lives.)</p>
 559<a name="cross2" />
 560<p><a href="#cross2">2) gcc+musl = musl-cross-make</a></p>
 562<p>The cross compilers I test this with are built from the
 563<a href=>musl-libc</a> maintainer's
 564<a href=>musl-cross-make</a>
 565project, built by running toybox's scripts/ in that directory,
 566and then symlink the resulting "ccc" subdirectory into toybox where
 567"make root CROSS=" can find them, ala:</p>
 570cd ~
 571git clone
 572git clone
 573cd musl-cross-make
 574../toybox/scripts/ # this takes a while
 575ln -s $(realpath ccc) ../toybox/ccc
 578<p>Instead of symlinking ccc, you can specify a CROSS_COMPILE= prefix
 579in the same format the Linux kernel build uses. You can either provide a
 580full path in the CROSS_COMPILE string, or add the appropriate bin directory
 581to your $PATH. I.E:</p>
 584<b><p>make LDFLAGS=--static CROSS_COMPILE=~/musl-cross-make/ccc/m68k-linux-musl-cross/bin/m68k-linux-musl- distclean defconfig toybox</p></b>
 587<p>Is equivalent to:</p>
 590export "PATH=~/musl-cross-make/ccc/m68k-linux-musl-cross/bin:$PATH"<br />
 591LDFLAGS=--static make distclean defconfig toybox CROSS=m68k-linux-musl-
 594<p>Note: these examples use static linking becausae a dynamic musl binary
 595won't run on your host unless you install musl's into the system
 596libraries (which is an accident waiting to happen adding a second C library
 597to most glibc linux distribution) or play with $LD_LIBRARY_PATH.
 598In theory you could "make root" a dynamic root filesystem with musl by copying
 599the shared libraries out of the toolchain, but I haven't bothered implementing
 600that in mkroot yet because a static linked musl hello world is 10k on x86
 601(5k if stripped).</p>
 603<a name="cross3" />
 604<p><a href="#cross3">3) llvm+bionic = Android NDK</a></p>
 606<p>The <a href=>Android
 607Native Development Kit</a> provides an llvm toolchain with the bionic
 608libc used by Android. To turn it into something toybox can use, you
 609just have to add an appropriately prefixed "cc" symlink to the other
 610prefixed tools, ala:</p>
 614cd android-ndk-21b/toolchains/llvm/prebuilt/linux-x86_64/bin
 615ln -s x86_64-linux-android29-clang x86_64-linux-android-cc
 617cd ~/toybox
 618make distclean
 619make LDFLAGS=--static CROSS_COMPILE=x86_64-linux-android- defconfig toybox
 622<p>Again, you need to static link unless you want to install bionic on your
 623host. Binaries statically linked against bionic are almost as big as with
 624glibc, but at least it doesn't have the dlopen() issues. (You still can't
 625sanely use dlopen() from a static binary, but bionic doesn't use dlopen()
 626internally to implement basic features.)</p>
 628<p>Note: although the resulting toybox will run in a standard
 629Linux system, even "hello world"
 630statically linked against bionic segfaults before calling main()
 631when /dev/null isn't present. This presents mkroot with a chicken and
 632egg problem for both chroot and qemu cases, because mkroot's init script
 633has to mount devtmpfs on /dev to provide /dev/null before the shell binary
 634can run mkroot's init script.
 635Since mkroot runs as a normal user, we can't "mknod dev/null" at build
 636time to create a "null" device in the filesystem we're packaging up so
 637initramfs doesn't start with an empty /dev, and the
 638<a href=>kernel</a>
 639<a href=>developers</a>
 640<a href=>repeatedly</a>
 641<a href=>rejected</a> a patch to
 642make the Linux kernel honor DEVTMPFS_MOUNT in initramfs. Teaching toybox
 643cpio to accept synthetic filesystem metadata,
 644presumably in <a href=>get_init_cpio</a> format, remains a todo item.</p>
 646<hr /><h2><a name="system" />Q: What part of Linux/Android does toybox provide?</h2>
 649Toybox is one of three packages (linux, libc, command line) which together provide a bootable unix-style command line operating system.
 650Toybox provides the "command line" part, with a
 651<a href=>bash</a> compatible
 652<a href=>command line interpreter</a>
 653and over two hundred <a href=>commands</a>
 654to call from it, as documented in
 655<a href=>posix</a>,
 656the <a href=>Linux Standard Base</a>, and the
 657<a href=>Linux Manual
 660<p>Toybox is not by itself a complete operating system, it's a set of standard command line utilities that run in an operating system.
 661Booting a simple system to a shell prompt requires a kernel to drive the hardware (such as Linux, or BSD with a Linux emulation layer), programs for the system to run (such as toybox's commands), and a C library ("libc") to connect them together.</p>
 663<p>Toybox has a policy of requiring no external dependencies other than the
 664kernel and C library (at least for defconfig builds). You can optionally enable support for
 665additional libraries in menuconfig (such as openssl, zlib, or selinux),
 666but toybox either provides its own built-in versions of such functionality
 667(which the libraries provide larger, more complex, often assembly optimized
 668alternatives to), or allows things like selinux support to cleanly drop
 671<p>Static linking (with the --static option) copies library contents
 672into the resulting binary, creating larger but more portable programs which
 673can run even if they're the only file in the filesystem. Otherwise,
 674the "dynamically" linked programs require each shared library file to be
 675present on the target system, either copied out of the toolchain or built
 676again from source (with potential version skew if they don't match the toolchain
 677versions exactly), plus a dynamic linker executable installed at a specific
 678absolute path. See the
 679<a href=>ldd</a>,
 680<a href=></a>,
 681and <a href=>libc</a>
 682man pages for details.</p>
 684<p>Most embedded systems will add another package to the kernel/libc/cmdline
 685above containing the dedicated "application" that the embedded system exists to
 686run, plus any other packages that application depends on.
 687Build systems add a native version of the toolchain packages so
 688they can compile additional software on the resulting system. Desktop systems
 689add a GUI and additional application packages like web browsers
 690and video players. A linux distro like Debian adds hundreds of packages.
 691Android adds around a thousand.</p>
 693<p>But all of these systems conceptually sit on a common three-package
 694"kernel/libc/cmdline" base (often inefficiently implemented and broken up
 695into more packages), and toybox aims to provide a simple, reproducible,
 696auditable version of the cmdline portion of that base.</p>
 698<hr /><h2><a name="mkroot" />Q: How do you build a working Linux system with toybox?</h2>
 700<p>A: Toybox has a built-in <a href=>system builder</a>, with the Makefile target "<b>make
 701root</b>". To enter the resulting root filesystem, "<b>sudo chroot
 702root/host/fs /init</b>". Type "exit" to get back out.</p>
 704<p>You can cross compile simple three package (toybox+libc+linux)
 705systems configured to boot to a shell prompt under the emulator
 706<a href=>qemu</a>
 707by specifying a target type with CROSS=
 708(or by setting CROSS_COMPILE= to a <a href=#cross>cross compiler</a> prefix with optional absolute
 709path), and pointing the build at a Linux kernel source directory, ala:</p>
 711<blockquote><p><b>make root CROSS=sh4 LINUX=~/linux</b></p></blockquote>
 713<p>Then you can <b>cd root/sh4; ./</b> to launch the emulator.
 714(You'll need the appropriate qemu-system-* emulator binary installed.)
 715Type "exit" when done and it should shut down the emulator on the way out,
 716similar to exiting the chroot version. (Except this is more like you ssh'd
 717to a remote machine: the emulator created its own CPU with its own memory
 718and I/O devices, and booted a kernel in it.)</p>
 720<p>The build finds the <a href=#system>three packages</a> needed to produce
 721this system because 1) you're in a toybox source directory, 2) your cross
 722compiler has a libc built into it, 3) you tell it where to find a Linux kernel
 723source directory with LINUX= on the command line. If you don't say LINUX=,
 724it skips that part of the build and just produces a root filesystem directory
 725ala the first example in this FAQ answer.</p>
 727<p>The CROSS= shortcut expects a "ccc" symlink in the toybox source directory
 728pointing at a directory full of cross compilers. The ones I test this with are built from the musl-libc
 730<a href=>musl-cross-make</a>
 731project, built by running toybox's scripts/ in that directory,
 732and then symlink the resulting "ccc" subdirectory into toybox where CROSS=
 733can find them:</p>
 736cd ~
 737git clone
 738git clone
 739cd musl-cross-make
 740../toybox/scripts/ # this takes a while
 741ln -s $(realpath ccc) ../toybox/ccc
 744<p>If you don't want to do that, you can download <a href=>prebuilt binary versions</a> from Zach van Rijn's site and
 745just extract them into a "ccc" subdirectory under the toybox source.</p>
 747<p>Once you've installed the cross compilers, "<b>make root CROSS=help</b>"
 748should list all the available cross compilers it recognizes under ccc,
 749something like:</p>
 752aarch64 armv4l armv5l armv7l armv7m armv7r i486 i686 m68k microblaze mips mips64 mipsel powerpc powerpc64 powerpc64le s390x sh2eb sh4 x32 x86_64
 755<p>(A long time ago I
 756<a href=>tried to explain</a>
 757what some of these architectures were.)</p>
 759<p>You can build all the targets at once, and can add additonal packages
 760to the build, by calling the script directly and listing packages on
 761the command line:</p>
 764<p><b>scripts/ CROSS=all LINUX=~/linux dropbear</b></p>
 767<p>An example package build script (building the dropbear ssh server, adding a
 768port forward from to the qemu command line, and providing a convenience script to the output directory) is provided
 770in the scripts/root directory. If you add your own scripts elsewhere, just
 771give a path to them on the command line. (No, I'm not merging more package build
 772scripts, I <a href=>learned that lesson</a> long ago. But if you
 773want to write your own, feel free.)</p>
 775<p>(Note: currently cheats. If you don't have a .config it'll
 776make defconfig and add CONFIG_SH and CONFIG_ROUTE to it, because the new
 777root filesystem kinda needs those commands to function properly. If you already
 778have a .config that
 779_doesn't_ have CONFIG_SH in it, you won't get a shell prompt or be able to run
 780the init script without a shell. This is currently a problem because sh
 781and route are still in pending and thus not in defconfig, so "make root"
 782cheats and adds them. I'm working on it. tl;dr if make root doesn't work
 783"rm .config" and run it again, and all this should be fixed up in future when
 784those two commands are promoted out of pending so "make defconfig" would have
 785what you need anyway. It's designed to let yout tweak your config, which is
 786why it uses the .config that's there when there is one, but the default is
 787currently wrong because it's not quite finished yet. All this should be
 788cleaned up in a future release, before 1.0.)</p>
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