環境は wsl2 の debian sid、ruby は rbenv で入れた2.7.4。 追記: Ubuntu 20.04.3 on wsl2 ,ruby 2.7.4p191 でもほぼ同じ手順で RMagick をインストールできました。 ❯ gem install rmagick Building native extensions. This could take a while... ERROR: Error installing rmagick: ERROR: Failed to build gem native extension. current directory: /home/tsut/.rbenv/versions/2.7.4/lib/ruby/gems/2.7.0/gems/rmagick-4.2.3/ext/RMagick /home/tsut/.rbenv/versions/2.7.4/bin/ruby -I /home/tsut/.rbenv/versions/2.7.4/lib/ruby/2.7.0 -r ./siteconf20211014-1879-j0t0tw.rb extconf.rb checking for brew... no checking for pacman... no checking for Ruby version >= 2.3.0... yes checking for pkg-config... yes Package MagickCore was not found in the pkg-config search path. Perhaps you should add the directory containing `MagickCore.pc' to the PKG_CONFIG_PATH environment variable No package 'MagickCore' found MagickCore.pc が見つからないって言ってるらしい。 ぐぐるとRM