class CurrentProcess

def self.change_privilege(user, group = user)
  uid, gid = Process.euid, Process.egid
  target_uid = Etc.getpwnam(user).uid
  target_gid = Etc.getgrnam(group).gid
  if uid != target_uid || gid != target_gid
    Process.initgroups(user, target_gid)
    Process::GID.change_privilege(target_gid)
    Process::UID.change_privilege(target_uid)
  end
rescue Errno::EPERM => e
  raise "Couldn't change user and group to #{user}:#{group}: #{e}"
end