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posix_spawn(3POSIX) was introduced by POSIX.1d
(IEEE Std 1003.1d-1999), and was later consolidated in
POSIX.1-2001, requiring it in all POSIX-compliant systems.
It's safe to assume it's always available, more than 20 years
after its standardization.
Link: <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/spawn.h.html>
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Now the nxt_user_groups_get() function uses getgrouplist(3) when available
(except MacOS, see below). For some platforms, getgrouplist() supports
a method of probing how much groups the user has but the behavior is not
consistent. The method used here consists of optimistically trying to get up
to min(256, NGROUPS_MAX) groups; only if ngroups returned exceeds the original
value, we do a second call. This method can block main's process if LDAP/NDIS+
is in use.
MacOS has getgrouplist(3) but it's buggy. It doesn't update ngroups if the
value passed is smaller than the number of groups the user has. Some
projects (like Go stdlib) call getgrouplist() in a loop, increasing ngroups
until it exceeds the number of groups user belongs to or fail when a limit
is reached. For performance reasons, this is to be avoided and MacOS is
handled in the fallback implementation.
The fallback implementation is the old Unit approach. It saves main's
user groups (getgroups(2)) and then calls initgroups(3) to load application's
groups in main, then does a second getgroups(2) to store the gids and restore
main's groups in the end. Because of initgroups(3)' call to setgroups(2),
this method requires root capabilities. In the case of OSX, which has
small NGROUPS_MAX by default (16), it's not possible to restore main's groups
if it's large; if so, this method fallbacks again: user_cred gids aren't
stored, and the worker process calls initgroups() itself and may block for
some time if LDAP/NDIS+ is in use.
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In particular, it was previously broken on Ubuntu 19.10 and Fedora 31.
See for details: https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=2ab5741
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Prodded by David Carlier.
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The interface is available since Glibc 2.25, and FreeBSD 12.0.
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Configuration and building example:
./configure
./configure python
./configure php
./configure go
make all
or
./configure
make nginext
./configure python
make python
./configure php
make php
./configure go
make go
Modules configuration options and building examples:
./configure python --module=python2 --config=python2.7-config
make python2
./configure php --module=php7 --config=php7.0-config
--lib-path=/usr/local/php7.0
make php7
./configure go --go=go1.6 --go-path=${HOME}/go1.6
make go1.6
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