Lines from "vagrant up" that are highlighted in my terminal (yellow or red) and one line before and after, for context:

$ vagrant up
...
==> default: Machine booted and ready!
GuestAdditions versions on your host (4.3.16) and guest (4.3.10) do not match.
stdin: is not a tty
...
mount: block device /tmp/VBoxGuestAdditions.iso is write-protected, mounting read-only
Installing Virtualbox Guest Additions 4.3.16 - guest version is 4.3.10
stdin: is not a tty
...
Could not find the X.Org or XFree86 Window System, skipping.
An error occurred during installation of VirtualBox Guest Additions 4.3.16. Some functionality may not work as intended.
In most cases it is OK that the "Window System drivers" installation failed.
stdin: is not a tty
...
==> default: Notice: /Stage[main]/Mediawiki/Php::Composer::Install[/vagrant/mediawiki]/Exec[composer-install--vagrant-mediawiki]/returns: To initialize a project, please create a composer.json file as described in the http://getcomposer.org/ "Getting Started" section
==> default: Error: composer install --optimize-autoloader returned 1 instead of one of [0]
==> default: Error: /Stage[main]/Mediawiki/Php::Composer::Install[/vagrant/mediawiki]/Exec[composer-install--vagrant-mediawiki]/returns: change from notrun to 0 failed: composer install --optimize-autoloader returned 1 instead of one of [0]
==> default: Notice: /Stage[main]/Mediawiki/Mediawiki::Wiki[devwiki]/File[/vagrant/settings.d/wikis/wiki]/ensure: created
...
==> default: Notice: /Stage[main]/Mediawiki/Mediawiki::Skin[Vector]/Git::Clone[mediawiki/skins/Vector]/Exec[git_clone_mediawiki/skins/Vector]/returns: fatal: destination path '/vagrant/mediawiki/skins/Vector' already exists and is not an empty directory.
==> default: Error: git clone --recurse-submodules   https://gerrit.wikimedia.org/r/p/mediawiki/skins/Vector.git /vagrant/mediawiki/skins/Vector returned 128 instead of one of [0]
==> default: Error: /Stage[main]/Mediawiki/Mediawiki::Skin[Vector]/Git::Clone[mediawiki/skins/Vector]/Exec[git_clone_mediawiki/skins/Vector]/returns: change from notrun to 0 failed: git clone --recurse-submodules   https://gerrit.wikimedia.org/r/p/mediawiki/skins/Vector.git /vagrant/mediawiki/skins/Vector returned 128 instead of one of [0]
==> default: Notice: /Stage[main]/Mediawiki/File[/var/www/mediawiki-vagrant.png]/ensure: defined content as '{md5}f9afb7d19e39247820bc1e81883a96f7'
...
==> default: Notice: /Stage[main]/Mediawiki/Mediawiki::Skin[Vector]/Mediawiki::Settings[Vector]/File[/vagrant/settings.d/puppet-managed/10-Vector.php]: Dependency Exec[git_clone_mediawiki/skins/Vector] has failures: true
==> default: Warning: /Stage[main]/Mediawiki/Mediawiki::Skin[Vector]/Mediawiki::Settings[Vector]/File[/vagrant/settings.d/puppet-managed/10-Vector.php]: Skipping because of failed dependencies
==> default: Notice: /Stage[main]/Mediawiki::Jobrunner/File[/etc/init/jobrunner.conf]/ensure: defined content as '{md5}e2302b512e81c3d406f8f2159dd4dbcd'
...
==> default: Notice: Finished catalog run in 180.74 seconds
The SSH command responded with a non-zero exit status. Vagrant
assumes that this means the command failed. The output for this command
should be in the log above. Please read the output to determine what
went wrong.