課題
WSL2環境に、wsl用のcudaをインストールした場合、cudnn8がレポジトリーに含まれておらず、インストールができません（2022/10/23現在）
このwsl用のレポジトリーに、libcudnn8*が無いんです。
次の方法でインストールできました。
もっと適切な方法があるのかもしれませんが、これでインストールできて、使えました。
ubuntu用のレポジトリーからパッケージを取得
wget https://developer.download.nvidia.com/compute/cuda/repos/ubuntu2004/x86_64/libcudnn8-dev_8.0.5.39-1+cuda11.1_amd64.deb
wget https://developer.download.nvidia.com/compute/cuda/repos/ubuntu2004/x86_64/libcudnn8_8.0.5.39-1+cuda11.1_amd64.deb
インストール
$ sudo apt install ./libcudnn8-dev_8.0.5.39-1+cuda11.1_amd64.deb ./libcudn
n8_8.0.5.39-1+cuda11.1_amd64.deb
Reading package lists... Done
Building dependency tree
Reading state information... Done
Note, selecting 'libcudnn8-dev' instead of './libcudnn8-dev_8.0.5.39-1+cuda11.1_amd64.deb'
Note, selecting 'libcudnn8' instead of './libcudnn8_8.0.5.39-1+cuda11.1_amd64.deb'
The following NEW packages will be installed:
libcudnn8 libcudnn8-dev
0 upgraded, 2 newly installed, 0 to remove and 294 not upgraded.
Need to get 0 B/896 MB of archives.
After this operation, 4567 MB of additional disk space will be used.
Get:1 /home/masa/deeplearning4/4.2/gridworld/libcudnn8_8.0.5.39-1+cuda11.1_amd64.deb libcudnn8 amd64 8.0.5.39-1+cuda11.1 [506 MB]
Get:2 /home/masa/deeplearning4/4.2/gridworld/libcudnn8-dev_8.0.5.39-1+cuda11.1_amd64.deb libcudnn8-dev amd64 8.0.5.39-1+cuda11.1 [389 MB]
Selecting previously unselected package libcudnn8.
(Reading database ... 77559 files and directories currently installed.)
Preparing to unpack .../libcudnn8_8.0.5.39-1+cuda11.1_amd64.deb ...
Unpacking libcudnn8 (8.0.5.39-1+cuda11.1) ...
Selecting previously unselected package libcudnn8-dev.
Preparing to unpack .../libcudnn8-dev_8.0.5.39-1+cuda11.1_amd64.deb ...
Unpacking libcudnn8-dev (8.0.5.39-1+cuda11.1) ...
Setting up libcudnn8 (8.0.5.39-1+cuda11.1) ...
Setting up libcudnn8-dev (8.0.5.39-1+cuda11.1) ...
update-alternatives: using /usr/include/x86_64-linux-gnu/cudnn_v8.h to provide /usr/include/cudnn.h (libcudnn) in auto mode