VBoxLinuxAdditions.run を実行して Unit vboxadd.service not loaded. になった時の対応方法 ref: http://qiita.com/ponsuke0531/items/886d4295a9088de25145

file0.txt

$ sudo sh /mnt/cdrom/VBoxLinuxAdditions.run
Verifying archive integrity... All good.
Uncompressing VirtualBox 5.1.22 Guest Additions for Linux...........
VirtualBox Guest Additions installer
You appear to have a version of the VirtualBox Guest Additions
on your system which was installed from a different source or using a
different type of installer.  If you installed it from a package from your
Linux distribution or if it is a default part of the system then we strongly
recommend that you cancel this installation and remove it properly before
installing this version.  If this is simply an older or a damaged
installation you may safely proceed.

Do you wish to continue anyway? [yes or no] y
Copying additional installer modules ...
Installing additional modules ...
vboxadd.sh: Starting the VirtualBox Guest Additions.
Failed to set up service vboxadd, please check the log file
/var/log/VBoxGuestAdditions.log for details.

$ vi /var/log/VBoxGuestAdditions.log
▼▼▼▼▼▼▼▼▼▼▼▼ VBoxGuestAdditions.logの中身 ▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼
Redirecting to /bin/systemctl stop  vboxadd-x11.service
Failed to stop vboxadd-x11.service: Unit vboxadd-x11.service not loaded.
Redirecting to /bin/systemctl stop  vboxvfs.service
Failed to stop vboxvfs.service: Unit vboxvfs.service not loaded.
Redirecting to /bin/systemctl stop  vboxadd-timesync.service
Failed to stop vboxadd-timesync.service: Unit vboxadd-timesync.service not loaded.
Redirecting to /bin/systemctl stop  vboxadd-service.service
Failed to stop vboxadd-service.service: Unit vboxadd-service.service not loaded.
Redirecting to /bin/systemctl stop  vboxadd.service
Failed to stop vboxadd.service: Unit vboxadd.service not loaded.
vboxadd.sh: failed: Configuration file /var/lib/VBoxGuestAdditions/config not found.
vboxadd.sh: failed: Look at /var/log/vboxadd-install.log to find out what went wrong.
vboxadd.sh: failed: Look at /var/log/vboxadd-install.log to find out what went wrong.
vboxadd.sh: failed: modprobe vboxguest failed.

file1.txt

$ shutdown -h now
==== AUTHENTICATING FOR org.freedesktop.login1.power-off ===
Authentication is required for powering off the system.
Authenticating as: mana
Password: 
==== AUTHENTICATION COMPLETE ===
Connection to 192.168.0.6 closed by remote host.
Connection to 192.168.0.6 closed.

file2.txt

$ sudo mount /dev/cdrom /mnt/cdrom/
[sudo] password for mana: 
mount: /dev/sr0 is write-protected, mounting read-only
$ sudo sh /mnt/cdrom/VBoxLinuxAdditions.run