init.pp

class sethostname {
  file { "/etc/hostname":
    ensure => present,
    owner => root,
    group => root,
    mode => 644,
    content => "$::fqdn\n",
    notify => Exec["set-hostname"],
  }
  exec { "set-hostname":
    command => "/bin/hostname -F /etc/hostname",
    unless => "/usr/bin/test `hostname` = `/bin/cat /etc/hostname`",
    notify => Service[$rsyslog::params::service_name],
  }
}