From: "mbideau (Michael Bideau) via ruby-core" <ruby-core@...>
Date: 2026-10-14T13:12:14+00:00
Subject: [ruby-core:127103] [Ruby Bug#22438] mkmf.rb do not work with /home mounted with noexec

Issue #22438 has been reported by mbideau (Michael Bideau).

----------------------------------------
Bug #22438: mkmf.rb do not work with /home mounted with noexec
https://bugs.ruby-lang.org/issues/22438

* Author: mbideau (Michael Bideau)
* Status: Open
* ruby -v: ruby 3.3.8 (2025-04-09 revision b200bad6cd) [x86_64-linux-gnu]
* Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN
----------------------------------------
When trying to install a *vagrant* plugin (here *vagrant-libvirt*), it uses the file **mkmf.rb** (here `/opt/vagrant/embedded/lib/ruby/3.3.0/mkmf.rb`) and this fail with the following error message:
> Vagrant failed to install the requested plugin because development tools
are required for installation but are not currently installed on this
machine. Please install development tools and then try this command
again.

It is the user facing error message that is from the following underlying command:
```
/opt/vagrant/embedded/bin/ruby --verbose extconf.rb
checking for pkg-config for libvirt... /opt/vagrant/embedded/lib/ruby/3.3.0/mkmf.rb:480:in `try_do': The compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.

	from /opt/vagrant/embedded/lib/ruby/3.3.0/mkmf.rb:573:in `try_link0'
	from /opt/vagrant/embedded/lib/ruby/3.3.0/mkmf.rb:591:in `try_link'
	from /opt/vagrant/embedded/lib/ruby/3.3.0/mkmf.rb:683:in `try_ldflags'
	from /opt/vagrant/embedded/lib/ruby/3.3.0/mkmf.rb:1896:in `block in pkg_config'
	from /opt/vagrant/embedded/lib/ruby/3.3.0/mkmf.rb:983:in `block in checking_for'
	from /opt/vagrant/embedded/lib/ruby/3.3.0/mkmf.rb:344:in `block (2 levels) in postpone'
	from /opt/vagrant/embedded/lib/ruby/3.3.0/mkmf.rb:314:in `open'
	from /opt/vagrant/embedded/lib/ruby/3.3.0/mkmf.rb:344:in `block in postpone'
	from /opt/vagrant/embedded/lib/ruby/3.3.0/mkmf.rb:314:in `open'
	from /opt/vagrant/embedded/lib/ruby/3.3.0/mkmf.rb:340:in `postpone'
	from /opt/vagrant/embedded/lib/ruby/3.3.0/mkmf.rb:982:in `checking_for'
	from /opt/vagrant/embedded/lib/ruby/3.3.0/mkmf.rb:1862:in `pkg_config'
	from extconf.rb:5:in `<main>'
```

The mentioned `try_do` function is where the issue is.
Here is its code (as the ruby version 3.3.8):
```ruby
  def try_do(src, command, *opts, &b)
    unless have_devel?
      raise <<MSG
The compiler failed to generate an executable file.
You have to install development tools first.
MSG
    end
    begin
      src = create_tmpsrc(src, &b)
      xsystem(command, *opts)
    ensure
      log_src(src)
    end
  end
```

Which is called by `try_link0` function that has the following code:
```ruby
  def try_link0(src, opt="", *opts, &b) # :nodoc:
    exe = CONFTEST+$EXEEXT
    cmd = link_command("", opt)
    if $universal
      require 'tmpdir'
      Dir.mktmpdir("mkmf_", oldtmpdir = ENV["TMPDIR"]) do |tmpdir|
        begin
          ENV["TMPDIR"] = tmpdir
          try_do(src, cmd, *opts, &b)
        ensure
          ENV["TMPDIR"] = oldtmpdir
        end
      end
    else
      try_do(src, cmd, *opts, &b)
    end and File.executable?(exe) or return nil
    exe
  ensure
    MakeMakefile.rm_rf(*Dir["#{CONFTEST}*"]-[exe])
  end
```

So you can see, if my understanding is correct, that the environment variable`TMPDIR`, despite being set, is never used/honored to execute the command.
The command is still running in the current working directory, and the `TMPDIR` is ignored/useless.

In my case the current working directory is `~/.vagrant.d/gems/3.3.8/gems/ruby-libvirt-0.8.4/ext/libvirt` which is in my */home* mounted with `noexec`.
This makes `File.executable?(exe)` (`exe` is the compiled file) returning `false` because the source and the compiled file (even if they are just to test) end up in my working directory and not in the temporary directory specified with the environment variable **TMPDIR** which have `exec` permission.

So I suggest to always use a temporary directory to execute all the tests contained in this code file **mkmf.rb** and to actually honor `TMPDIR` when defined.



-- 
https://bugs.ruby-lang.org/
______________________________________________
 ruby-core mailing list -- ruby-core@ml.ruby-lang.org
 To unsubscribe send an email to ruby-core-leave@ml.ruby-lang.org
 ruby-core info -- https://ml.ruby-lang.org/mailman3/lists/ruby-core.ml.ruby-lang.org/