没有安装Virtual Box增强功能Guest Additions的虚拟机操作很不方便，比如：
- 虚拟机的分辨率最大只有1024×768；
- 鼠标被虚拟机捕获后要按右Ctrl键才能释放，否则只能再虚拟机里移动；
- 剪贴板不能共享
安装Guest Additions可以解决上述所有问题。
以CentOS 7.3虚拟机为例，如果安装CentOS时没有选择Development Tools组，需要先安装kernel-devel和gcc
$ sudo yum install -y kernel-devel gcc
通过VirtualBox的 设备 | 安装增强功能… 菜单可以加载VBoxGuestAdditions.iso，可以直接点击Run安装或者执行
$ cd /run/media/centos/VBOXADDITIONS_5.1.22_115126
$ sudo sh ./VBoxLinuxAdditions.run
有时安装会出错
Verifying archive integrity… All good.
Uncompressing VirtualBox 5.1.22 Guest Additions for Linux………..
VirtualBox Guest Additions installer
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.
查询log发现是找不到和Linux内核匹配的源文件
$ cat /var/log/VBoxGuestAdditions.log
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.
$ cat /var/log/vboxadd-install.log
/tmp/vbox.0/Makefile.include.header:112: *** Error: unable to find the sources of your current Linux kernel. Specify KERN_DIR= and run Make again. Stop.
Creating user for the Guest Additions.
Creating udev rule for the Guest Additions kernel module.
查询kernel-devel版本是3.10.0-514.26.2.el7.x86_64，而Linux内核版本是3.10.0-514.el7.x86_64，确实不一致。如果安装CentOS时选择了Development Tools组，kernel-devel版本和Linux内核版本是匹配的，则不会出现这个问题。
$ rpm -qa | grep kernel-devel
kernel-devel-3.10.0-514.26.2.el7.x86_64
$ uname -r
3.10.0-514.el7.x86_64
可以使用下面两个命令中的一个安装和Linux内核版本匹配的kernel-devel
$ sudo yum install -y "kernel-devel-uname-r == $(uname -r)"
$ sudo yum install -y kernel-devel-3.10.0-514.el7
然后再次安装Guest Additions成功
$ cd /run/media/centos/VBOXADDITIONS_5.1.22_115126
$ sudo sh ./VBoxLinuxAdditions.run
Verifying archive integrity… All good.
Uncompressing VirtualBox 5.1.22 Guest Additions for Linux………..
VirtualBox Guest Additions installer
Removing installed version 5.1.22 of VirtualBox Guest Additions…
Copying additional installer modules …
Installing additional modules …
vboxadd.sh: Starting the VirtualBox Guest Additions.
