Puppet::Util::Execution.execute 'hostname' returns nothing as daemon

When Puppet::Util::Execution.execute 'hostname' is invoked by Puppet running as a daemon, no output is written. This seems to be exclusive to hostname, and may be restricted to certain Linux versions. I've tried it on RedHat 7 (64-bit).

This can happen in a provider when using commands :hostname => 'hostname', and then invoking hostname. The root appears to be how /usr/bin/hostname handles file handles.

It can be simplified to

exec { '/bin/hostname': logoutput => true }

This is getting into some core Ruby weirdness:

ruby -e "Kernel.fork { \$stdout.reopen('/tmp/foo', 'w+'); Kernel.exec 'hostname' }"

prints hostname to /tmp/foo when run from the command-line. When run as a systemd script:

[Unit]

Description=Print the hostname using Ruby

Wants=basic.target

After=basic.target network.target

[Service]

ExecStart=/usr/bin/ruby -e "Kernel.fork { $stdout.reopen('/tmp/foo', 'w'); Kernel.exec 'hostname' }"

KillMode=process

[Install]

WantedBy=multi-user.target

symlinked to /etc/systemd/system/multi-user.target.wants/print-hostname.service it creates an empty file.

Changing the ruby script to

foo = open('/tmp/foo', 'w'); pid = Kernel.fork { $stdout.reopen(foo); Kernel.exec 'hostname' }; Process.wait pid; foo.close

to ensure the file is closed doesn't seem to change the behavior.

Also, behavior is consistent with both system Ruby on Redhat 7 (2.0.0) and Ruby with a puppet-agent 1.6.2 build candidate.

If I use a simple fork/exec without trying to redirect stdout, it prints correctly as a service and from the command-line. It's only once I redirect stdout that things get weird. The above is essentially what Puppet::Util::Execution.execute does, which is what the type is calling to. Interestingly, Facter::Core::Execution.execute (with Facter 3) works fine.

With strace, I note that hostname calls write(1, ...) then immediately exits. Other examples will close fids 1 and 2 before exiting.