about summary refs log tree commit diff
path: root/doc/manual/command-ref/conf-file.xml
blob: b1b604100f987381dd13b71f88030c07de9359f5 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
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
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
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
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
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
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
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
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
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
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
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
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
581
582
583
584
585
586
587
588
589
590
591
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
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
<refentry xmlns="http://docbook.org/ns/docbook"
          xmlns:xlink="http://www.w3.org/1999/xlink"
          xmlns:xi="http://www.w3.org/2001/XInclude"
          xml:id="sec-conf-file">

<refmeta>
  <refentrytitle>nix.conf</refentrytitle>
  <manvolnum>5</manvolnum>
  <refmiscinfo class="source">Nix</refmiscinfo>
  <refmiscinfo class="version"><xi:include href="../version.txt" parse="text"/></refmiscinfo>
</refmeta>

<refnamediv>
  <refname>nix.conf</refname>
  <refpurpose>Nix configuration file</refpurpose>
</refnamediv>

<refsection><title>Description</title>

<para>A number of persistent settings of Nix are stored in the file
<filename><replaceable>sysconfdir</replaceable>/nix/nix.conf</filename> or
<filename>$NIX_CONF_DIR/nix.conf</filename> if <envar>NIX_CONF_DIR</envar> is set.
This file is a list of <literal><replaceable>name</replaceable> =
<replaceable>value</replaceable></literal> pairs, one per line.
Comments start with a <literal>#</literal> character.  Here is an example
configuration file:</para>

<programlisting>
gc-keep-outputs = true       # Nice for developers
gc-keep-derivations = true   # Idem
env-keep-derivations = false
</programlisting>

<para>You can override settings using the <option>--option</option>
flag, e.g. <literal>--option gc-keep-outputs false</literal>.</para>

<para>The following settings are currently available:

<variablelist>


  <varlistentry xml:id="conf-gc-keep-outputs"><term><literal>gc-keep-outputs</literal></term>

    <listitem><para>If <literal>true</literal>, the garbage collector
    will keep the outputs of non-garbage derivations.  If
    <literal>false</literal> (default), outputs will be deleted unless
    they are GC roots themselves (or reachable from other roots).</para>

    <para>In general, outputs must be registered as roots separately.
    However, even if the output of a derivation is registered as a
    root, the collector will still delete store paths that are used
    only at build time (e.g., the C compiler, or source tarballs
    downloaded from the network).  To prevent it from doing so, set
    this option to <literal>true</literal>.</para></listitem>

  </varlistentry>


  <varlistentry xml:id="conf-gc-keep-derivations"><term><literal>gc-keep-derivations</literal></term>

    <listitem><para>If <literal>true</literal> (default), the garbage
    collector will keep the derivations from which non-garbage store
    paths were built.  If <literal>false</literal>, they will be
    deleted unless explicitly registered as a root (or reachable from
    other roots).</para>

    <para>Keeping derivation around is useful for querying and
    traceability (e.g., it allows you to ask with what dependencies or
    options a store path was built), so by default this option is on.
    Turn it off to save a bit of disk space (or a lot if
    <literal>gc-keep-outputs</literal> is also turned on).</para></listitem>

  </varlistentry>


  <varlistentry><term><literal>env-keep-derivations</literal></term>

    <listitem><para>If <literal>false</literal> (default), derivations
    are not stored in Nix user environments.  That is, the derivation
    any build-time-only dependencies may be garbage-collected.</para>

    <para>If <literal>true</literal>, when you add a Nix derivation to
    a user environment, the path of the derivation is stored in the
    user environment.  Thus, the derivation will not be
    garbage-collected until the user environment generation is deleted
    (<command>nix-env --delete-generations</command>).  To prevent
    build-time-only dependencies from being collected, you should also
    turn on <literal>gc-keep-outputs</literal>.</para>

    <para>The difference between this option and
    <literal>gc-keep-derivations</literal> is that this one is
    “sticky”: it applies to any user environment created while this
    option was enabled, while <literal>gc-keep-derivations</literal>
    only applies at the moment the garbage collector is
    run.</para></listitem>

  </varlistentry>


  <varlistentry xml:id="conf-build-max-jobs"><term><literal>build-max-jobs</literal></term>

    <listitem><para>This option defines the maximum number of jobs
    that Nix will try to build in parallel.  The default is
    <literal>1</literal>. The special value <literal>auto</literal>
    causes Nix to use the number of CPUs in your system.  It can be
    overridden using the <option
    linkend='opt-max-jobs'>--max-jobs</option> (<option>-j</option>)
    command line switch.</para></listitem>

  </varlistentry>


  <varlistentry xml:id="conf-build-cores"><term><literal>build-cores</literal></term>

    <listitem><para>Sets the value of the
    <envar>NIX_BUILD_CORES</envar> environment variable in the
    invocation of builders.  Builders can use this variable at their
    discretion to control the maximum amount of parallelism.  For
    instance, in Nixpkgs, if the derivation attribute
    <varname>enableParallelBuilding</varname> is set to
    <literal>true</literal>, the builder passes the
    <option>-j<replaceable>N</replaceable></option> flag to GNU Make.
    It can be overridden using the <option
    linkend='opt-cores'>--cores</option> command line switch and
    defaults to <literal>1</literal>.  The value <literal>0</literal>
    means that the builder should use all available CPU cores in the
    system.</para></listitem>

  </varlistentry>


  <varlistentry xml:id="conf-build-max-silent-time"><term><literal>build-max-silent-time</literal></term>

    <listitem>

      <para>This option defines the maximum number of seconds that a
      builder can go without producing any data on standard output or
      standard error.  This is useful (for instance in an automated
      build system) to catch builds that are stuck in an infinite
      loop, or to catch remote builds that are hanging due to network
      problems.  It can be overridden using the <option
      linkend="opt-max-silent-time">--max-silent-time</option> command
      line switch.</para>

      <para>The value <literal>0</literal> means that there is no
      timeout.  This is also the default.</para>

    </listitem>

  </varlistentry>


  <varlistentry xml:id="conf-build-timeout"><term><literal>build-timeout</literal></term>

    <listitem>

      <para>This option defines the maximum number of seconds that a
      builder can run.  This is useful (for instance in an automated
      build system) to catch builds that are stuck in an infinite loop
      but keep writing to their standard output or standard error.  It
      can be overridden using the <option
      linkend="opt-timeout">--timeout</option> command line
      switch.</para>

      <para>The value <literal>0</literal> means that there is no
      timeout.  This is also the default.</para>

    </listitem>

  </varlistentry>


  <varlistentry xml:id="conf-build-max-log-size"><term><literal>build-max-log-size</literal></term>

    <listitem>

      <para>This option defines the maximum number of bytes that a
      builder can write to its stdout/stderr.  If the builder exceeds
      this limit, it’s killed.  A value of <literal>0</literal> (the
      default) means that there is no limit.</para>

    </listitem>

  </varlistentry>


  <varlistentry xml:id="conf-build-users-group"><term><literal>build-users-group</literal></term>

    <listitem><para>This options specifies the Unix group containing
    the Nix build user accounts.  In multi-user Nix installations,
    builds should not be performed by the Nix account since that would
    allow users to arbitrarily modify the Nix store and database by
    supplying specially crafted builders; and they cannot be performed
    by the calling user since that would allow him/her to influence
    the build result.</para>

    <para>Therefore, if this option is non-empty and specifies a valid
    group, builds will be performed under the user accounts that are a
    member of the group specified here (as listed in
    <filename>/etc/group</filename>).  Those user accounts should not
    be used for any other purpose!</para>

    <para>Nix will never run two builds under the same user account at
    the same time.  This is to prevent an obvious security hole: a
    malicious user writing a Nix expression that modifies the build
    result of a legitimate Nix expression being built by another user.
    Therefore it is good to have as many Nix build user accounts as
    you can spare.  (Remember: uids are cheap.)</para>

    <para>The build users should have permission to create files in
    the Nix store, but not delete them.  Therefore,
    <filename>/nix/store</filename> should be owned by the Nix
    account, its group should be the group specified here, and its
    mode should be <literal>1775</literal>.</para>

    <para>If the build users group is empty, builds will be performed
    under the uid of the Nix process (that is, the uid of the caller
    if <envar>NIX_REMOTE</envar> is empty, the uid under which the Nix
    daemon runs if <envar>NIX_REMOTE</envar> is
    <literal>daemon</literal>).  Obviously, this should not be used in
    multi-user settings with untrusted users.</para>

    </listitem>

  </varlistentry>


  <varlistentry><term><literal>build-use-sandbox</literal></term>

    <listitem><para>If set to <literal>true</literal>, builds will be
    performed in a <emphasis>sandboxed environment</emphasis>, i.e.,
    they’re isolated from the normal file system hierarchy and will
    only see their dependencies in the Nix store, the temporary build
    directory, private versions of <filename>/proc</filename>,
    <filename>/dev</filename>, <filename>/dev/shm</filename> and
    <filename>/dev/pts</filename> (on Linux), and the paths configured with the
    <link linkend='conf-build-sandbox-paths'><literal>build-sandbox-paths</literal>
    option</link>. This is useful to prevent undeclared dependencies
    on files in directories such as <filename>/usr/bin</filename>. In
    addition, on Linux, builds run in private PID, mount, network, IPC
    and UTS namespaces to isolate them from other processes in the
    system (except that fixed-output derivations do not run in private
    network namespace to ensure they can access the network).</para>

    <para>Currently, sandboxing only work on Linux and Mac OS X. The use
    of a sandbox requires that Nix is run as root (so you should use
    the <link linkend='conf-build-users-group'>“build users”
    feature</link> to perform the actual builds under different users
    than root).</para>

    <para>If this option is set to <literal>relaxed</literal>, then
    fixed-output derivations and derivations that have the
    <varname>__noChroot</varname> attribute set to
    <literal>true</literal> do not run in sandboxes.</para>

    <para>The default is <literal>false</literal>.</para>

    </listitem>

  </varlistentry>


  <varlistentry xml:id="conf-build-sandbox-paths">
    <term><literal>build-sandbox-paths</literal></term>

    <listitem><para>A list of paths bind-mounted into Nix sandbox
    environments. You can use the syntax
    <literal><replaceable>target</replaceable>=<replaceable>source</replaceable></literal>
    to mount a path in a different location in the sandbox; for
    instance, <literal>/bin=/nix-bin</literal> will mount the path
    <literal>/nix-bin</literal> as <literal>/bin</literal> inside the
    sandbox. If <replaceable>source</replaceable> is followed by
    <literal>?</literal>, then it is not an error if
    <replaceable>source</replaceable> does not exist; for example,
    <literal>/dev/nvidiactl?</literal> specifies that
    <filename>/dev/nvidiactl</filename> will only be mounted in the
    sandbox if it exists in the host filesystem.</para>

    <para>Depending on how Nix was built, the default value for this option
    may be empty or provide <filename>/bin/sh</filename> as a
    bind-mount of <command>bash</command>.</para></listitem>

  </varlistentry>


  <varlistentry xml:id="conf-build-extra-sandbox-paths">
    <term><literal>build-extra-sandbox-paths</literal></term>

    <listitem><para>A list of additional paths appended to
    <option>build-sandbox-paths</option>. Useful if you want to extend
    its default value.</para></listitem>

  </varlistentry>


  <varlistentry><term><literal>build-use-substitutes</literal></term>

    <listitem><para>If set to <literal>true</literal> (default), Nix
    will use binary substitutes if available.  This option can be
    disabled to force building from source.</para></listitem>

  </varlistentry>


  <varlistentry><term><literal>build-fallback</literal></term>

    <listitem><para>If set to <literal>true</literal>, Nix will fall
    back to building from source if a binary substitute fails.  This
    is equivalent to the <option>--fallback</option> flag.  The
    default is <literal>false</literal>.</para></listitem>

  </varlistentry>


  <varlistentry><term><literal>build-keep-log</literal></term>

    <listitem><para>If set to <literal>true</literal> (the default),
    Nix will write the build log of a derivation (i.e. the standard
    output and error of its builder) to the directory
    <filename>/nix/var/log/nix/drvs</filename>.  The build log can be
    retrieved using the command <command>nix-store -l
    <replaceable>path</replaceable></command>.</para></listitem>

  </varlistentry>


  <varlistentry><term><literal>build-compress-log</literal></term>

    <listitem><para>If set to <literal>true</literal> (the default),
    build logs written to <filename>/nix/var/log/nix/drvs</filename>
    will be compressed on the fly using bzip2.  Otherwise, they will
    not be compressed.</para></listitem>

  </varlistentry>


  <varlistentry><term><literal>use-binary-caches</literal></term>

    <listitem><para>If set to <literal>true</literal> (the default),
    Nix will check the binary caches specified by
    <option>binary-caches</option> and related options to obtain
    binary substitutes.</para></listitem>

  </varlistentry>


  <varlistentry><term><literal>binary-caches</literal></term>

    <listitem><para>A list of URLs of binary caches, separated by
    whitespace.  The default is
    <literal>https://cache.nixos.org</literal>.</para></listitem>

  </varlistentry>


  <varlistentry><term><literal>binary-caches-files</literal></term>

    <listitem><para>A list of names of files that will be read to
    obtain additional binary cache URLs.  The default is
    <literal>/nix/var/nix/profiles/per-user/<replaceable>username</replaceable>/channels/binary-caches/*</literal>.
    Note that when you’re using the Nix daemon,
    <replaceable>username</replaceable> is always equal to
    <literal>root</literal>, so Nix will only use the binary caches
    provided by the channels installed by root.  Do not set this
    option to read files created by untrusted users!</para></listitem>

  </varlistentry>


  <varlistentry><term><literal>trusted-binary-caches</literal></term>

    <listitem><para>A list of URLs of binary caches, separated by
    whitespace.  These are not used by default, but can be enabled by
    users of the Nix daemon by specifying <literal>--option
    binary-caches <replaceable>urls</replaceable></literal> on the
    command line.  Unprivileged users are only allowed to pass a
    subset of the URLs listed in <literal>binary-caches</literal> and
    <literal>trusted-binary-caches</literal>.</para></listitem>

  </varlistentry>


  <varlistentry><term><literal>extra-binary-caches</literal></term>

    <listitem><para>Additional binary caches appended to those
    specified in <option>binary-caches</option> and
    <option>binary-caches-files</option>.  When used by unprivileged
    users, untrusted binary caches (i.e. those not listed in
    <option>trusted-binary-caches</option>) are silently
    ignored.</para></listitem>

  </varlistentry>


  <varlistentry><term><literal>signed-binary-caches</literal></term>

    <listitem><para>If set to <literal>*</literal>, Nix will only
    download binaries if they are signed using one of the keys listed
    in <option>binary-cache-public-keys</option>.</para></listitem>

  </varlistentry>


  <varlistentry><term><literal>binary-cache-public-keys</literal></term>

    <listitem><para>A whitespace-separated list of public keys
    corresponding to the secret keys trusted to sign binary
    caches. For example:
    <literal>cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
    hydra.nixos.org-1:CNHJZBh9K4tP3EKF6FkkgeVYsS3ohTl+oS0Qa8bezVs=</literal>.</para></listitem>

  </varlistentry>


  <varlistentry><term><literal>binary-caches-parallel-connections</literal></term>

    <listitem><para>The maximum number of parallel TCP connections
    used to fetch files from binary caches and by other downloads. It
    defaults to 25. 0 means no limit.</para></listitem>

  </varlistentry>


  <varlistentry><term><literal>verify-https-binary-caches</literal></term>

    <listitem><para>Whether HTTPS binary caches are required to have a
    certificate that can be verified. Defaults to
    <literal>true</literal>.</para></listitem>

  </varlistentry>


  <varlistentry><term><literal>netrc-file</literal></term>

    <listitem><para>If set to an absolute path to a <filename>netrc</filename>
    file, Nix will use the HTTP authentication credentials in this file when
    trying to download from a remote host through HTTP or HTTPS. Defaults to
    <filename>$NIX_CONF_DIR/netrc</filename>.</para>

    <para>The <filename>netrc</filename> file consists of a list of
    accounts in the following format:

<screen>
machine <replaceable>my-machine</replaceable>
login <replaceable>my-username</replaceable>
password <replaceable>my-password</replaceable>
</screen>

    For the exact syntax, see <link
    xlink:href="https://ec.haxx.se/usingcurl-netrc.html">the
    <literal>curl</literal> documentation.</link></para></listitem>

  </varlistentry>


  <varlistentry><term><literal>system</literal></term>

    <listitem><para>This option specifies the canonical Nix system
    name of the current installation, such as
    <literal>i686-linux</literal> or
    <literal>x86_64-darwin</literal>.  Nix can only build derivations
    whose <literal>system</literal> attribute equals the value
    specified here.  In general, it never makes sense to modify this
    value from its default, since you can use it to ‘lie’ about the
    platform you are building on (e.g., perform a Mac OS build on a
    Linux machine; the result would obviously be wrong).  It only
    makes sense if the Nix binaries can run on multiple platforms,
    e.g., ‘universal binaries’ that run on <literal>x86_64-linux</literal> and
    <literal>i686-linux</literal>.</para>

    <para>It defaults to the canonical Nix system name detected by
    <filename>configure</filename> at build time.</para></listitem>

  </varlistentry>


  <varlistentry><term><literal>fsync-metadata</literal></term>

    <listitem><para>If set to <literal>true</literal>, changes to the
    Nix store metadata (in <filename>/nix/var/nix/db</filename>) are
    synchronously flushed to disk.  This improves robustness in case
    of system crashes, but reduces performance.  The default is
    <literal>true</literal>.</para></listitem>

  </varlistentry>


  <varlistentry><term><literal>auto-optimise-store</literal></term>

    <listitem><para>If set to <literal>true</literal>, Nix
    automatically detects files in the store that have identical
    contents, and replaces them with hard links to a single copy.
    This saves disk space.  If set to <literal>false</literal> (the
    default), you can still run <command>nix-store
    --optimise</command> to get rid of duplicate
    files.</para></listitem>

  </varlistentry>


  <varlistentry xml:id="conf-connect-timeout"><term><literal>connect-timeout</literal></term>

    <listitem>

      <para>The timeout (in seconds) for establishing connections in
      the binary cache substituter.  It corresponds to
      <command>curl</command>’s <option>--connect-timeout</option>
      option.</para>

    </listitem>

  </varlistentry>


  <varlistentry xml:id="conf-log-servers"><term><literal>log-servers</literal></term>

    <listitem>

      <para>A list of URL prefixes (such as
      <literal>http://hydra.nixos.org/log</literal>) from which
      <command>nix-store -l</command> will try to fetch build logs if
      they’re not available locally.</para>

    </listitem>

  </varlistentry>


  <varlistentry xml:id="conf-trusted-users"><term><literal>trusted-users</literal></term>

    <listitem>

      <para>A list of names of users (separated by whitespace) that
      have additional rights when connecting to the Nix daemon, such
      as the ability to specify additional binary caches, or to import
      unsigned NARs. You can also specify groups by prefixing them
      with <literal>@</literal>; for instance,
      <literal>@wheel</literal> means all users in the
      <literal>wheel</literal> group. The default is
      <literal>root</literal>.</para>

      <warning><para>The users listed here have the ability to
      compromise the security of a multi-user Nix store. For instance,
      they could install Trojan horses subsequently executed by other
      users. So you should consider carefully whether to add users to
      this list.</para></warning>

    </listitem>

  </varlistentry>


  <varlistentry xml:id="conf-allowed-users"><term><literal>allowed-users</literal></term>

    <listitem>

      <para>A list of names of users (separated by whitespace) that
      are allowed to connect to the Nix daemon. As with the
      <option>trusted-users</option> option, you can specify groups by
      prefixing them with <literal>@</literal>. Also, you can allow
      all users by specifying <literal>*</literal>. The default is
      <literal>*</literal>.</para>

      <para>Note that trusted users are always allowed to connect.</para>

    </listitem>

  </varlistentry>


  <varlistentry xml:id="conf-restrict-eval"><term><literal>restrict-eval</literal></term>

    <listitem>

      <para>If set to <literal>true</literal>, the Nix evaluator will
      not allow access to any files outside of the Nix search path (as
      set via the <envar>NIX_PATH</envar> environment variable or the
      <option>-I</option> option). The default is
      <literal>false</literal>.</para>

    </listitem>

  </varlistentry>


  <varlistentry xml:id="conf-pre-build-hook"><term><literal>pre-build-hook</literal></term>

    <listitem>


      <para>If set, the path to a program that can set extra
      derivation-specific settings for this system. This is used for settings
      that can't be captured by the derivation model itself and are too variable
      between different versions of the same system to be hard-coded into nix.
      </para>

      <para>The hook is passed the derivation path and, if sandboxes are enabled,
      the sandbox directory. It can then modify the sandbox and send a series of
      commands to modify various settings to stdout. The currently recognized
      commands are:</para>

      <variablelist>
        <varlistentry xml:id="extra-sandbox-paths">
          <term><literal>extra-sandbox-paths</literal></term>

          <listitem>

            <para>Pass a list of files and directories to be included in the
            sandbox for this build. One entry per line, terminated by an empty
            line. Entries have the same format as
            <literal>build-sandbox-paths</literal>.</para>

          </listitem>

        </varlistentry>
      </variablelist>
    </listitem>

  </varlistentry>


  <varlistentry xml:id="conf-build-repeat"><term><literal>build-repeat</literal></term>

    <listitem><para>How many times to repeat builds to check whether
    they are deterministic. The default value is 0. If the value is
    non-zero, every build is repeated the specified number of
    times. If the contents of any of the runs differs from the
    previous ones, the build is rejected and the resulting store paths
    are not registered as “valid” in Nix’s database.</para></listitem>

  </varlistentry>


  <varlistentry xml:id="conf-sandbox-dev-shm-size"><term><literal>sandbox-dev-shm-size</literal></term>

    <listitem><para>This option determines the maximum size of the
    <literal>tmpfs</literal> filesystem mounted on
    <filename>/dev/shm</filename> in Linux sandboxes. For the format,
    see the description of the <option>size</option> option of
    <literal>tmpfs</literal> in
    <citerefentry><refentrytitle>mount</refentrytitle><manvolnum>8</manvolnum></citerefentry>. The
    default is <literal>50%</literal>.</para></listitem>

  </varlistentry>


  <varlistentry xml:id="conf-allow-import-from-derivation"><term><literal>allow-import-from-derivation</literal></term>

    <listitem><para>By default, nix allows you to <function>import</function> from a derivation,
    allowing building at evaluation time. With this option set to false, nix will throw an error
    when evaluating an expression that uses this feature, allowing users to ensure their evaluation
    will not require any builds to take place.</para></listitem>

  </varlistentry>


</variablelist>

</para>

</refsection>

</refentry>