packer error

gistfile1.txt

    virtualbox-iso: + [[ -n 4.3.46(1)-release ]]
    virtualbox-iso: + export -fn __rvm_select_version_variables __rvm_ruby_string_parse_ __rvm_rm_rf_verbose __rvm_parse_args
    virtualbox-iso: + return 0
    virtualbox-iso: + return 0
    virtualbox-iso: + true
    virtualbox-iso: + mkdir /tmp/isomount
    virtualbox-iso: + mount -t iso9660 -o loop /home/vagrant/VBoxGuestAdditions.iso /tmp/isomount
    virtualbox-iso: mount: /dev/loop0 is write-protected, mounting read-only
    virtualbox-iso: + /tmp/isomount/VBoxLinuxAdditions.run
    virtualbox-iso: Verifying archive integrity... All good.
    virtualbox-iso: Uncompressing VirtualBox 5.1.28 Guest Additions for Linux...........
    virtualbox-iso: VirtualBox Guest Additions installer
    virtualbox-iso: Copying additional installer modules ...
    virtualbox-iso: Installing additional modules ...

    virtualbox-iso: vboxadd.sh: Starting the VirtualBox Guest Additions.
    virtualbox-iso:
    virtualbox-iso: Could not find the X.Org or XFree86 Window System, skipping.
==> virtualbox-iso: Step "StepProvision" failed, aborting...
Build 'virtualbox-iso' errored: unexpected EOF

==> Some builds didn't complete successfully and had errors:
--> virtualbox-iso: unexpected EOF

==> Builds finished but no artifacts were created.