* helpers: lockfree lookup of nobody user on linux and darwin
This PR continues the nobody user lookup saga, by making the nobody
user lookup lock-free on linux and darwin.
By doing the lookup in an init block this originally broke on Windows,
where we must avoid doing the lookup at all. We can get around that
breakage by only doing the lookup on linux/darwin where the nobody
user is going to exist.
Also return the nobody user by value so that a copy is created that
cannot be modified by callers of Nobody().
* helper: move nobody code into unix file
In #14742 we introduced a cached lookup of the `nobody` user, which is only ever
called on Unixish machines. But the initial caching was being done in an `init`
block, which meant it was being run on Windows as well. This prevents the Nomad
agent from starting on Windows.
An alternative fix here would be to have a separate `init` block for Windows and
Unix, but this potentially masks incorrect behavior if we accidentally added a
call to the `Nobody()` method on Windows later. This way we're forced to handle
the error in the caller.
* client: protect user lookups with global lock
This PR updates Nomad client to always do user lookups while holding
a global process lock. This is to prevent concurrency unsafe implementations
of NSS, but still enabling NSS lookups of users (i.e. cannot not use osusergo).
* cl: add cl
This PR adds support for the raw_exec driver on systems with only cgroups v2.
The raw exec driver is able to use cgroups to manage processes. This happens
only on Linux, when exec_driver is enabled, and the no_cgroups option is not
set. The driver uses the freezer controller to freeze processes of a task,
issue a sigkill, then unfreeze. Previously the implementation assumed cgroups
v1, and now it also supports cgroups v2.
There is a bit of refactoring in this PR, but the fundamental design remains
the same.
Closes#12351#12348
Fixes an issue where the Ruby runtime expects the sticky bit to be set
on the temp directory. The sticky bit is commonly set on the temp
directory since it is usually shared by many users. This change brings
ours in line with that assumption.
