nix/src/libstore/sandbox-defaults.sb

(define TMPDIR (param "_GLOBAL_TMP_DIR"))

; Disallow creating setuid/setgid binaries, since that
; would allow breaking build user isolation.
(deny file-write-setugid)

; Allow forking.
(allow process-fork)

; Allow reading system information like #CPUs, etc.
(allow sysctl-read)

; Allow POSIX semaphores and shared memory.
(allow ipc-posix*)

; Allow socket creation.
(allow system-socket)

; Allow sending signals within the sandbox.
(allow signal (target same-sandbox))

; Access to /tmp.
(allow file* process-exec (literal "/tmp") (subpath TMPDIR))

; Some packages like to read the system version.
(allow file-read* (literal "/System/Library/CoreServices/SystemVersion.plist"))

; Without this line clang cannot write to /dev/null, breaking some configure tests.
(allow file-read-metadata (literal "/dev"))

; Standard devices.
(allow file*
       (literal "/dev/null")
       (literal "/dev/random")
       (literal "/dev/stdin")
       (literal "/dev/stdout")
       (literal "/dev/tty")
       (literal "/dev/urandom")
       (literal "/dev/zero")
       (subpath "/dev/fd"))

; Does nothing, but reduces build noise.
(allow file* (literal "/dev/dtracehelper"))

; Allow access to zoneinfo since libSystem needs it.
(allow file-read* (subpath "/usr/share/zoneinfo"))

(allow file-read* (subpath "/usr/share/locale"))

; This is mostly to get more specific log messages when builds try to
; access something in /etc or /var.
(allow file-read-metadata
       (literal "/etc")
       (literal "/var")
       (literal "/private/var/tmp")
       )