我是 ubuntu 新手，我已在 USB 上安装了 ubuntu 并从它启动，我想测试我的显卡，因此想运行 glxgears 工具。当我输入以下命令来安装包时，它显示以下消息。ubuntu 正在从 usb 运行，请告知为什么无法安装。
ubuntu@ubuntu:~$ sudo apt-get install mesa-utils
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package mesa-utils is not available, but is referred to by another package.
This may mean that the package is
missing, has been obsoleted, or is only available from another source