language.txt 27.4 KB
Newer Older
1 2 3 4
The updater language
====================

This document is about the language describing specific update
5 6 7 8 9 10
scenarios. It is the core configuration language of the updater
itself, listing which packages should be installed, where they come
from and any special quirks needed for specific situations. Other ways
of configuring are possible (like command line requests to install
some packages, or listing things in UCI file), but these are usually
implemented in this language.
11 12 13 14 15 16

The language is, strictly speaking, ordinary Lua (currently the
supported version of Lua on OpenWRT is 5.1, but there should be very
little difference in what we use). Just the set of functions available
is limited to the functions listed here.

17 18
Note that using conditions, loops and variables is fully supported
and sometimes desirable.
19

20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72
Security levels
---------------

There are different security levels of the scripts used.  The security
level may further limit the set of commands and the abilities of given
commands. This is to ensure the server may never send malicious
commands covertly (it still can send version of package that contains
the malicious code, but that's impossible to prevent with
an auto-updater, but it would at least have to notify about the
package being installed).

Security levels are:

Full::
  The Lua code is not run in any sandbox at all. All functions here
  work without any limits. Also, all Lua libraries are available
  without any limitation and further Lua code can be required
  (including compiled `.so` modules). This is what the internals of the
  updater would be built in.
Local::
  It is possible to reference local files and directories as further
  configuration scripts. It is possible to read UCI configuration and
  execute arbitrary shell commands.
Remote::
  The functions may reference only other remote resources, not local
  ones. Reading UCI config is not possible.
Restricted::
  It is possible to further restrict the entities referenced to a
  string match (eg. ensure that it comes from a given server). Access
  to flag storage is restricted only to flags belonging to the current
  script and scripts it references.

No function allows raising the security level when referencing another
script.

Each script runs with its own environment ‒ they don't see each
other's variables.

Order of execution
------------------

The scripts are executed in the order they are referenced, in DFS
order. A referenced script is first fully executed (with its
sub-scripts) before the current script continues. In that sense, it
works similar to any other scripting language `include` command.

However, the execution of the script does not include installation of
packages. That happens after all the scripts terminated. The scripts
simply describe in what situation the OS should be.

It is possible to hook some functions in between (after, before)
installation of packages, or even between installation and
configuration.
73

74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95
Script names
------------

Each script has a name. The names form a tree structure and are used
to namespace various kinds of information, most importantly flag
storage.

Having two scripts of the same full name is an error. The name of the
script may be the same if it is referenced from different scripts.

The names are separated by a slash. The top-level built in script has
an empty name, but it doesn't store any information, only references
other scripts.

A script may reference other scripts by the names. An empty string
means itself. Names starting with slash are absolute ‒ they start from
the top-level script. Other names are relative and refer to
sub-scripts.

This is similar to filesystem paths. However, the `.` and `..` names
are not supported here.

96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125
URIs
----

Sometimes, an entity needs to be referenced somehow. Such entity may
live in the local filesystem or be on an external server.

These are the types of URIs supported:

* `file://`
* `http://`
* `https://`
* `data:`
* `internal:`

The remote ones (`http` and `https`) may need verification of the
integrity of its content. The other are considered secure and don't
need any kind of verification.

The `data:` is slightly limited compared to what the standard (RFC
2397) allows. The media type and charset are irrelevant to the
updater and are therefore not supported.

The `internal:` URI is a non-standard scheme. The updater may contain
compiled-in resources (embedded files). Each such resource has a
unique name. The `internal:` scheme accesses these embedded files. The
colon is directly followed by the name.

Scripts with access level of `remote` or lower are not allowed to use
the `file://` and `internal:` schemes.

126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161
Verification
------------

It is desirable to verify that the scripts and repository indices
weren't tampered with. It isn't needed to verify the packages (unless
they are stand-alone without repository), because the repository index
contains hashes of the packages.

There are two things we may verify. The server certificate (with the
`https` schema) and the file signature.

Each command that takes an URI as a parameter can have following extra
options:

verification::
  This specifies how the resource is verified. Possible values are
  (case insensitive):
  none;;
    Doesn't do any verification. This is the default for `file://`,
    `data://` and `internal://` URIs.
  cert;;
    Verify the server's SSL certificate.
  sig;;
    Verify file signature. This is the default for `http://` URIs.
  both;;
    Do both `cert` and `sig` verification. This is the default for
    `https://` URIs.
sig::
  URI where the signature of the resource lives. This one is not
  verified. If it isn't specified, it is constructed by adding `.sig`
  to the end of the verified URI. The option has effect only with
  `sig` and `both` verification.
pubkey::
  An URI or table of URIs with trusted public signature keys. These
  are not verified (therefore it is recommended to come from a already
  verified source ‒ like `data:` URI or `file://` URI). If it is not
162
  specified (`nil`), it is inherited from the verification of the script
163 164
  running the command. While it has no direct effect if the option is
  specified on another verification than `sig` or `both`, it
165
  influences the inheritance. Default value is `{}`.
166 167
ca::
  An URI or table of URIs with trusted SSL certificate authorities, in
168 169 170
  PEM format. Similar notes as with `pubkey` apply. But instead of table
  or URI you can also specify special value `system_cas`, which results
  into system authorities to be used. `system_cas` is also default value.
171
crl::
172 173 174 175
  An URI or table of URIs with CRLs relevant to the server. If set into
  `ignore_crl`, CRL is not checked. Note that the `crl` field is also
  inherited, therefore you may want to set it manually to `ignore_crl`.
  Default value is `ignore_crl`.
176 177 178 179 180 181

The file signature is verified using the `usign` utility.

Note that while a `remote` or `restricted` script may not specify
local (`file://` and `internal:`) URIs, it may inherit them.

182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215
Dependency description
----------------------

Package dependencies are very important part of package maintenance.
Therefore, it is possible to describe them in the updater.

A dependency might be one of:

string::
  The string is parsed the same way as from the OpenWRT packages.
  Dependencies are separated by commas, each ``word'' meaning a single
  dependency.  The dependencies can also use versions with relational
  operators.  The version with the operator is in parentheses after
  the name of the package (eg `kernel (=version-number)`, `openssl
  (>=1.0.0)`). As an extension, the operator `~` may be used to denote
  a lua string pattern match on the version. All dependencies and
  version restrictions must be met.
package handle::
  A concrete package, represented by the result of the `Package`
  command may be used directly.
table::
  The table shall contain multiple sub-dependencies. Each one must be
  met. The sub-dependency may be of any type (string, other table,
  package handle, `Or()`, `Not()`).
`Not(string)`::
  This denotes that a single package described by the string must not
  be present on the system. This may be used if two packages ``fight''
  over the same file, or when they provide colliding services (both
  are DNS servers, for example).
`Or(dep, dep, ...)`::
  Each `dep` argument is a dependency of any type. The whole `Or()` is
  fulfilled when at least one of the argument is fulfilled. When
  multiple options are possible, the leftmost of them is preferred.

216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233
Available commands
------------------

Most of the commands can be called in parenthesis mode, eg:

  Command("string", "string", {param = 1})

Or in a parentheses-less mode:

  Command "string" "string" {param = 1}

This is done by a trick with metatables returns a delayed morpher
object. It should be mostly invisible most of the time, though. The
result may be used as a handle to the created object and manipulate it
further.

Also, most of the commands start with a capital letter, since they act
as constructors.
234 235 236 237

Script
~~~~~~

238
  script = Script "script-name" "uri" { extra }
239 240 241 242

This command runs another script. The name is the local part of the
script name.

243
The uri provides the location of the script.
244 245

The last parameter is a table with extra information. It allows
246
fine-tuning the verification of URI and the way the script runs. The
247 248 249 250 251 252
current extra parameters are following.

security::
  Security level on which the script runs. It shall contain one of the
  above values. The name is case insensitive. It is not possible to
  raise the level, such attempt is reported as an error. If not
253
  specified, the level is deduced from the URI. If the URI is remote,
254 255
  it doesn't go above `remote`, otherwise it doesn't go above `local`.
restrict::
256
  If the level is `restricted`, this is the match for URIs that may be
257 258 259
  referenced. If the level is `restricted` and this is not specified,
  a match for the protocol and hostname is constructed. It has no
  effect with higher security levels.
260 261 262 263 264 265 266 267
ignore::
  Ignore certain errors. If they happen, don't process such script,
  but continue with the rest. This is a lua table with strings, each
  one specifying a category of erorrs to ignore.
  missing;;
    If the script can't be found.
  integrity;;
    Some signatures don't match.
268 269 270 271
verification::
sig::
pubkey::
ca::
272
crl::
273
  Options to verify the script integrity.
274 275 276 277

Repository
~~~~~~~~~~

278
  repository = Repository "repository-name" "uri" { extra }
279 280 281 282 283 284 285 286

This command introduces another repository of packages. The name may
be used as a reference from other commands and is used in error
messages. However, every place where the name may be used, the result
of the command may be used instead. It is legal to have multiple
repositories with the same name, but referencing it by name may
produce any of them. Referencing by the result is reliable.

287
The URI is expected to contain an OpenWRT repository in the format
288 289 290 291 292
produced by the buildroot.

Extra parameters are:

subdirs::
293
  If the URI contains multiple subdirectories, each one being a valid
294 295 296 297 298
  repository, you may list the subdirectories here (as a lua table of
  strings). The repository will unify all the subdirectory contents
  together to form one huge repository. In case of collision of
  packages between the subdirectories, the first one containing a
  given package wins (in the order listed here). If this option is not
299
  listed, the repository acts in normal way (the URI directly
300 301
  containing the packages).
index::
302 303 304
  Overrides the URI at which the repository index lives and uses the
  main URI as the place where packages are downloaded from. Both
  gzipped and plain versions may be in the given URI. If the option is
305
  not listed, it is expected to be in `Packages.gz`. Overriding the
306
  URI is not compatible with the subdirs option.
307 308 309 310 311 312 313
ignore::
  Ignore certain errors. This is a lua table with strings, each
  specifying a category of errors to ignore. If there's an error
  ignored, the repository acts as being empty. Otherwise, such error
  would cause the updater to stop.
  missing;;
    This error happens if the repository is not found. This can mean,
314
    for example, that the `https` URI where the index
315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331
    (`https://example.org/repository/Packages.gz`) returns 404.
    However, a missing package from the repository is not this kind of
    error (and cannot be ignored, because it is discovered late after
    planning what to install).
  integrity;;
    This is when the integrity verification/signature check fails.
    This may be caused by manipulation with the content, or by missing
    a key on our side.
  syntax;;
    It happens when the repository index can not be parsed because of
    syntax errors.
priority::
  In case of a package being available in multiple directories, the
  package is taken from the repository with highest priority. In case
  of equality, the one introduced first wins. The default when the
  option is not specified is 50. The number must be an integer between
  0 and 100.
332 333 334 335
verification::
sig::
pubkey::
ca::
336
crl::
337
  Options to verify the index integrity.
338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403

Uninstall
~~~~~~~~~

  Uninstall "package" "package" { extra } "package" "package" { extra }

This command takes multiple package names. It ensures none of the
packages is installed.

Note that this is not needed most of the time, since unneeded packages
are removed automatically.

Extra options modify the packages preceding them, but only up to the
previous extra options block. Therefore, the first two packages in the
example are modified by the first extra options block, the third and
fourth by the second block.

priority::
  In case of colliding requirements (the same package is required by
  an ``Install`` command or as a dependency of something), the
  requirement with the higher priority wins. In case of a draw, an
  error is reported. The priority defaults to 50 and must be between 0
  and 100.

Install
~~~~~~~

  Install "package" "package" { extra } "package" "package" { extra }

This command is the opposite of `Uninstall`. It requires that a
package be present in the system.

The resolving of extra options acts the same as with `Uninstall`.

Available extra options:

priority::
  Acts the same as with `Uninstall`.
version::
  Limits the considered versions. This may be a single string or a
  table with multiple strings. If there are multiple, each is
  considered a condition and all must pass for a version to be
  accepted. Using of operators `<`, `<=`, `>`, `>=` is possible. Also,
  if the version is prefixed with `~`, it acts as a lua string match
  pattern against the version. So this would accept versions between 3
  and 7 and ignore the `.0` ones: `{ ">=3.0", "<=7.0", "~^%d+%.[1-9]%d*" }`.
  The default is no condition, therefore all versions available pass.
  From the versions that match and satisfy all dependency
  requirements, the one with highest version is chosen. In case when
  no available version matches, the currently installed version is
  also considered as a fallback.
repository::
  Usually, all repositories are searched according to their
  priorities. If you specify this option as a lua table, only the
  repositories listed here are searched, in the order in the table
  (ignoring the global priority).
reinstall::
  When set to any value, the package is re-installed even if the
  chosen version is already installed.
critical::
  If set to any value, the package and all its dependencies are
  considered critical. The updater will try harder to have it in a
  consistent state or be able to at least fix it without access to
  network. Other packages may stop working if the update is
  interrupted at the wrong time (for example by a power outage), but
  would be fixed by another finished updater run.
404 405 406 407 408 409 410 411 412
ignore::
  Ignore certain errors regarding the installation request. Note that
  errors related to the package itself are modified by the `Package`
  command. This takes an array of strings, each string represents one
  category of errors to ignore.
  missing;;
    Don't fail on the package not being available. The package
    wouldn't be installed if not available, but the run of the updater
    wouldn't be aborted.
413 414 415 416 417 418 419 420 421 422 423 424 425 426 427

Note that a package may be required to be installed or uninstalled
multiple times (for example by multiple scripts). All such
requirements are tried to be met (eg. by unifying the version options,
etc).

Package
~~~~~~~

  package = Package "name" { extra }

This command allows amending a package from a repository. It allows
for adding dependencies (even negative or alternative dependencies).
It allows for specifying hooks ‒ functions that are run at specific
times. It also allows creation of virtual packages ‒ a package that
428
doesn't really exist, but can participates in the dependency computation.
429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445

A package may be amended multiple times. Each time the options are
merged into the package options.

The result may be used instead of a package name in the dependencies
of other packages and in `Install` and `Uninstall` commands.

Also, the name parameter is optional. If it is omitted (either
specified as nil or just left out), an unique name is generated. This
is useful only for virtual packages.

The options are:

virtual::
  If set to any value, the package is virtual. If a real package of
  the same name exists, an error is reported.
deps::
446 447 448
  Additional dependencies for the package. The dependencies are merged
  together as if all the sources were put into a table (eg. all of
  them must be fulfilled). There's no way to remove dependencies.
449 450
order_after::
order_before::
451 452 453 454 455 456
  Usually, all dependencies of a package are installed before the
  package. Sometimes, it may be desirable to break this order and
  these options allow that. Both of them list packages after or before
  which the current package shall be installed, in a table. This
  allows breaking dependency cycles. These options are mere hint, the
  updater may decide to not follow them if it is not possible to
457 458
  satisfy. Note that this has effect only on running the pre_* and
  post_* scripts and hooks, since all the files of all updated
459
  packages are merged into the system together.
460 461
pre_*::
post_*::
462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493
  A hook to be run after or before a step. The value may be a single
  function or a table of functions. All the functions (from the table
  or merged from multiple `Package` commands) are run, in unspecified
  order. TODO: List the steps and what commands may be used inside the
  functions.
reboot::
  A reboot is needed when installing the package. The reboot is
  scheduled according to the value.
  delayed;;
    The package needs a reboot for the new version to take effect, but
    the old version works, so it may be delayed for arbitrary amount
    of time.
  finished;;
    The reboot needs to be done once the update is finished. It is
    because the old version no longer works as expected. The whole
    update may be delayed because the need of this update, so the
    update happens at a time convenient to the user.
  immediate;;
    The reboot needs to be done just after the package is set up. This
    may be needed when the old version would prevent the rest of the
    update from happening.
replan::
  The package has an effect on the updater itself. Therefore,
  interrupt the update after this package is set up and perform the
  planning again.
abi_change::
  The package changed its ABI (or some other interface) and some other
  packages need to be reinstalled. If this is set to `true` and the
  package is installed or updated, all packages that depend on it are
  reinstalled. If it is set to a table, it lists packages that need to
  be reinstalled. When merging `true` to a table, `true` is considered
  to be the list of packages depending on this one.
494 495 496 497 498
abi_change_deep::
  Same as abi_change, but also reinstall packages that depends indirectly on
  package that changed its ABI. That means if some package is reinstalled because
  of change of ABI, all packages that depends on it are also reinstalled and so
  on.
499 500
content::
  This is an alternative for the package being available from a
501 502 503
  repository. This lists an URI where the package lives. If the
  package has all parameters same as one from a repository (eg.
  priority, version), the one with content is preferred.
504 505 506 507
verification::
sig::
pubkey::
ca::
508
crl::
509 510 511
  Options to verify the package integrity, if the content option is
  specified. These are ignored in virtual packages and packages from a
  repository.
512 513 514 515 516
priority::
  A priority for packages not coming from a repository (eg. with the
  `content` option) to be used when choosing the right candidate.
  Defaults to 50, as with repositories. It is ignored with packages
  from repositories and has no meaning for virtual packages.
517 518 519 520 521 522 523 524 525 526 527 528 529
ignore::
  Ignore listed categories of errors. This takes an array of strings,
  each string meaning one category to ignore.
  deps;;
    Don't error on missing dependencies. Simply install the package
    without satisfying the dependency.
  validation;;
    Install the package despite it failing validation (eg. when having
    different checksum).
  installation;;
    Don't report errors of installation in this package as an error
    and don't abort the rest of the installation process even if it is
    in an early stage.
530 531 532
  content::
    Don't error on missing content. If it's available from repository
    then it is handled as missing.
Michal 'vorner' Vaner's avatar
Michal 'vorner' Vaner committed
533

534 535 536 537 538 539 540 541 542 543
StoreFlags
~~~~~~~~~~

  StoreFlags "flagname" "flagname"

A script may request to store some of its flags right away, no matter
how the updater terminates. It first stores its flags and then calls
the `StoreFlags` command with the names of the flags to store. The
rest of the flags are stored as usual.

544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580
Run
~~~

  result = Run "command" "param" "param" "param" ... { extra }

This command is available only in `local` and `full` security levels.

This runs an external command. The `command` and `param` specify what to
run. The extra parameters are optional and may specify:

stdin::
  A string passed into the commands stdin. If not set, `/dev/null` is
  redirected there.
timeout::
  A timeout in seconds. If it is reached and the command haven't
  terminated yet, a SIGTERM is sent to the command. Nothing is sent if
  not specified.
timeout_kill::
  This is the same as with timeout, but SIGTERM is sent.

The `result` is a table with information about the command run. It
contains:

ecode::
  The numeric exit code of the command.
crashed::
  If present, the command terminated with a signal. The signal is the
  value associated with the key.
stdout::
  String containing the standard output of the command.
stderr::
  String containing the error output of the command.

Note that the command is not run interactively ‒ there's no way to
communicate with the command. It is started, runs with preset input
and then the output is presented.

581 582 583 584 585 586 587 588 589 590 591
Logging
~~~~~~~

  DBG "debug text"
  INFO "information text"
  WARN "warning text"
  ERROR "error text"

These commands allows printing of messages for their corresponding
verbosity levels.

592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627
Variables
---------

There are several global variables. These are set anew for each script
run, so one script can't damage them for another. Modifying them has
no effect on the updater's behaviour, unless specifically mentioned.
Note that some of the tables might be generated on demand by
meta-table events, making it impossible to list keys.

serial
~~~~~~

The variable contains the serial number of the device. It may be `nil`
in case it is not supported on the given device.

architectures
~~~~~~~~~~~~~

Allowed package architectures (in a table).

model
~~~~~

Content of `/tmp/sysinfo/model`. Might be nil on non-OpenWRT systems.

board_name
~~~~~~~~~~

Content of `/tmp/sysinfo/board_name`. Might be nil on non-OpenWRT
systems.

turris_version
~~~~~~~~~~~~~~

Content of `/etc/turris-version`. Might be nil on non-Turris systems.

628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651
self_version
~~~~~~~~~~~~

String containing version of updater.

language_version
~~~~~~~~~~~~~~~~

Number signaling version of updater configuration language used. This
is always `1` for language described in this document.

features
~~~~~~~~

Set of features current updater supports. You can check for feature
this way: `features['feature']`. These are currently available features:

priorities::
  Updater handles priorities between multiple requests for same package.
provides::
  Updater supports `Provides` control field.
abi_change::
  Updater can handle and propagate ABI change.

652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669
installed
~~~~~~~~~

This is a table of installed packages. The keys are package names and
values are tables with following keys:

version::
  The installed version.
files::
  Files belonging to the package (a table).
configs::
  Configuration files belonging to the package (a table).
repository::
  Name of the repository it has been installed from. It may be missing
  in case it is a package provided outside of a repository. Note that
  the name corresponds to the time the package has been installed and
  that repository may be unavailable now or the name represent a
  different repository.
670
install_time::
671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688
  Unix timestamp specifying when the package has been installed, in
  UTC.

The top-level table is instantiated (not generated through
meta-tables), therefore it is possible to get the list of installed
packages.

flags
~~~~~

A table with flags defined by the scripts. Flags are preserved between
the updater runs, so a script may leave notes for its future self.

The table is indexed by the name of the script, either relative or
absolute. Referencing self as an empty string works. The table is
generated on the fly, therefore the script may not find out what other
scripts ever run.

689 690 691 692 693
In case of the own flags, the table is fully instantiated, so they can
be written and iterated (using `next` and `pairs`). If it is flags
belonging to other script, the table is read only and doesn't allow
iterating (eg. it is possible to query a flag value, but not possible
to discover which flags exist).
694 695 696 697 698 699

Flags may be only strings.

Any modification to the own flags table is stored on successful
updater termination or when the script explicitly request it.

700 701
Hooks
-----
702

703 704 705 706 707 708 709 710
As the hooks are run after all the dependencies have been resolved and
plan has been made, it is no longer possible to call the `Repositor`,
`Package`, `Install` and `Uninstall` commands. These commands may be
used in addition to the rest:

Reboot
~~~~~~

711
  Reboot "when"
712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730

Restarts the OS. It is recommended to use the `reboot` option in the
`Package` command instead, since the updater would know about it in
advance and may, for example, wait for the user to confirm before
doing anything.

The when parameter may be either:

now::
  Don't finish the rest of updater, reboot right now. This is
  dangerous and should not be used unless necessary, since the rest of
  hooks for the given package may be lost. Installation of other
  packages will resume after reboot.
eventually::
  It will reboot at the end of the updater work.

Rerun
~~~~~

731
  Rerun "when"
732 733 734 735

Run the updater once more. The when has a similar meaning as with
`Reboot`. However, it won't resume installation after executing `now`.

736 737 738 739 740 741
The only parameter of the hook is a package object. It is a table that
has all the meaningful options from the `Package` and `Install`
commands and the ones from `installed` variable. However, with options
listing multiple possibilities, only the one chosen is kept. Also,
additional `name` option is included.

742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764
Available libraries and standard functions
------------------------------------------

In addition to the functions listed above, following functions and
libraries are made available. They are available in the security level
listed and in all higher levels.

Restricted::
  * `table` library.
  * `string` library.
  * `math` library.
  * `assert`.
  * `error`.
  * `ipairs`.
  * `next`.
  * `pairs`.
  * `pcall`.
  * `select`.
  * `tonumber`.
  * `tostring`.
  * `type`.
  * `unpack`.
  * `xpcall`.
765 766 767 768
  * `DBG`.
  * `INFO`.
  * `WARN`.
  * `ERROR`.
769 770 771 772
Local::
  * `uci` library.
Full::
  * The whole lua library.