目前virtualbox只有fedora32的rpm包，没有fedora33的。
去VirtualBox官网下载VirtualBox-6.1-6.1.18_142142_fedora32-1.x86_64.rpm，用sudo rpm -i命令安装：
[octopus@pc3 Downloads]$ sudo rpm -ivh VirtualBox-6.1-6.1.18_142142_fedora32-1.x86_64.rpm
warning: VirtualBox-6.1-6.1.18_142142_fedora32-1.x86_64.rpm: Header V4 DSA/SHA1 Signature, key ID 98ab5139: NOKEY
error: Failed dependencies:
python(abi) = 3.8 is needed by VirtualBox-6.1-6.1.18_142142_fedora32-1.x86_64
提示python的版本号不对，参照nothing provides python(abi) = 3.8 needed by VirtualBox-6.1-6.1.16_140961_fedora32-1.x86_64 - 张同光 - 博客园给出的解决方法，用rpmrebuild工具修改rpm里面的版本要求：
$ sudo dnf install rpmrebuild
$ rpmrebuild --change-spec-requires='sed -e "s/python(abi) = 3.8/python(abi) >= 3.8/"' --package VirtualBox-6.1-6.1.18_142142_fedora32-1.x86_64.rpm
（省略一大堆警告消息）
最后提示修改后的rpm文件路径：
result: /home/octopus/rpmbuild/RPMS/x86_64/VirtualBox-6.1-6.1.18_142142_fedora32-1.x86_64.rpm
安装修改后的rpm包：
[octopus@pc3 Downloads]$ cd ../rpmbuild/RPMS/x86_64/
[octopus@pc3 x86_64]$ ls
VirtualBox-6.1-6.1.18_142142_fedora32-1.x86_64.rpm
[octopus@pc3 x86_64]$ sudo rpm -ivh VirtualBox-6.1-6.1.18_142142_fedora32-1.x86_64.rpm
[sudo] password for octopus:
Verifying... ################################# [100%]
Preparing... ################################# [100%]
Updating / installing...
1:VirtualBox-6.1-6.1.18_142142_fedo################################# [100%]
Creating group 'vboxusers'. VM users must be member of that group!
安装成功！
还有更简单的安装方法。在官网上点击All distributions (built on EL6 and therefore not requiring recent system libraries)链接，下载VirtualBox-6.1.18-142142-Linux_amd64.run，赋予文件执行权限后，直接运行就能完成安装了：
[octopus@pc3 Downloads]$ chmod +x VirtualBox-6.1.18-142142-Linux_amd64.run
[octopus@pc3 Downloads]$ sudo ./VirtualBox-6.1.18-142142-Linux_amd64.run
Verifying archive integrity... All good.
Uncompressing VirtualBox for Linux installation.............
VirtualBox Version 6.1.18 r142142 (2021-01-07T16:56:51Z) installer
Installing VirtualBox to /opt/VirtualBox
Python found: python2, installing bindings...
VirtualBox has been installed successfully.
You will find useful information about using VirtualBox in the user manual
/opt/VirtualBox/UserManual.pdf
and in the user FAQ
http://www.virtualbox.org/wiki/User_FAQ
We hope that you enjoy using VirtualBox.
[octopus@pc3 Downloads]$
这两种安装方法安装6.1.18版本后，都遇到了全屏模式下鼠标左右键完全失效的问题（主机和虚拟机都无法控制），只能移动鼠标指针，现在还不知道怎么解决.。。
安装老版本VirtualBox-5.2.44-139111-Linux_amd64.run又安装不上，提示找不到<linux/smp_lock.h>文件。
但只要不去碰全屏模式上面的virtualbox菜单，鼠标就不会失效。可以在虚拟机设置里面将菜单隐藏，避免无意中碰到菜单导致鼠标按键失效。
关于sudo /sbin/vboxconfig报错的问题：
[octopus@pc3 ~]$ sudo /sbin/vboxconfig
[sudo] password for octopus:
vboxdrv.sh: Stopping VirtualBox services.
vboxdrv.sh: Starting VirtualBox services.
vboxdrv.sh: Building VirtualBox kernel modules.
vboxdrv.sh: failed: Look at /var/log/vbox-setup.log to find out what went wrong.
There were problems setting up VirtualBox. To re-start the set-up process, run
/sbin/vboxconfig
as root. If your system is using EFI Secure Boot you may need to sign the
kernel modules (vboxdrv, vboxnetflt, vboxnetadp, vboxpci) before you can load
them. Please see your Linux system's documentation for more information.
/tmp/vbox.0/linux/VBoxNetFlt-linux.c: In function ‘vboxNetFltNeedsLinkState’:
/tmp/vbox.0/linux/VBoxNetFlt-linux.c:1761:47: error: dereferencing pointer to incomplete type ‘const struct ethtool_ops’
1761 | if (pDev->ethtool_ops && pDev->ethtool_ops->get_drvinfo)
| ^~
/tmp/vbox.0/linux/VBoxNetFlt-linux.c:1763:32: error: storage size of ‘Info’ isn’t known
1763 | struct ethtool_drvinfo Info;
| ^~~~
/tmp/vbox.0/linux/VBoxNetFlt-linux.c:1766:20: error: ‘ETHTOOL_GDRVINFO’ undeclared (first use in this function)
1766 | Info.cmd = ETHTOOL_GDRVINFO;
| ^~~~~~~~~~~~~~~~
/tmp/vbox.0/linux/VBoxNetFlt-linux.c:1766:20: note: each undeclared identifier is reported only once for each function it appears in
/tmp/vbox.0/linux/VBoxNetFlt-linux.c:1763:32: warning: unused variable ‘Info’ [-Wunused-variable]
1763 | struct ethtool_drvinfo Info;
| ^~~~
make[2]: *** [scripts/Makefile.build:279: /tmp/vbox.0/linux/VBoxNetFlt-linux.o] Error 1
make[1]: *** [Makefile:1800: /tmp/vbox.0] Error 2
make: *** [/tmp/vbox.0/Makefile-footer.gmk:117: vboxnetflt] Error 2
修改/opt/VirtualBox/src/vboxhost/vboxnetflt/linux/VBoxNetFlt-linux.c文件，添加#include <linux/ethtool.h>即可解决问题。
[octopus@pc3 ~]$ sudo /sbin/vboxconfig
vboxdrv.sh: Stopping VirtualBox services.
vboxdrv.sh: Starting VirtualBox services.
vboxdrv.sh: Building VirtualBox kernel modules.
------------------------------------------------------------------
2021-05-01：Fedora34+VirtualBox6.1.22仍然没有解决鼠标指针失效的bug。而且还新增了一个bug：隐藏全屏菜单后，鼠标指针完全消失，不显示。点鼠标右键又能弹出右键菜单，但就是不显示鼠标指针。
还是老老实实用窗口模式吧！最好把虚拟机里面旧的增强工具卸载了，再重装最新的。
------------------------------------------------------------------
2023-01-25：卸载用脚本安装的VirualBox6.1.22。
先解压压缩包到a文件夹（不需要用sudo）。
[octopus@pc3 Downloads]$ mkdir a
[octopus@pc3 Downloads]$ ./VirtualBox-6.1.22-144080-Linux_amd64.run --target a
Creating directory a
Verifying archive integrity... All good.
Uncompressing VirtualBox for Linux installation.............
VirtualBox Version 6.1.22 r144080 (2021-04-28T16:54:09Z) installer
This program must be run with administrator privileges. Aborting
然后执行其中的uninstall脚本。
[octopus@pc3 Downloads]$ cd a
[octopus@pc3 a]$ sudo ./uninstall.sh
[sudo] password for octopus:
VirtualBox 6.1.22 r144080 has been removed successfully.
[octopus@pc3 a]$ cd ..
[octopus@pc3 Downloads]$ rm -rf a
