YARNのインストールができない【Error：EACCES】

環境

OS：macOS Monterey 12.0.1

問題

ターミナルで　npm install --global yarn　を実行すると、以下のようなEACCESエラーが発生

npm ERR! code EACCES
npm ERR! syscall mkdir
npm ERR! path /usr/local/lib/node_modules/yarn
npm ERR! errno -13
npm ERR! Error: EACCES: permission denied, mkdir '/usr/local/lib/node_modules/yarn'
npm ERR!  [Error: EACCES: permission denied, mkdir '/usr/local/lib/node_modules/yarn'] {
npm ERR!   errno: -13,
npm ERR!   code: 'EACCES',
npm ERR!   syscall: 'mkdir',
npm ERR!   path: '/usr/local/lib/node_modules/yarn'
npm ERR! }
npm ERR! 
npm ERR! The operation was rejected by your operating system.
npm ERR! It is likely you do not have the permissions to access this file as the current user
npm ERR! 
npm ERR! If you believe this might be a permissions issue, please double-check the
npm ERR! permissions of the file and its containing directories, or try running
npm ERR! the command again as root/Administrator.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/miyu/.npm/_logs/2021-11-06T14_30_15_414Z-debug.log

解決方法

以下のnpm公式ドキュメントの通りに２つの解決手順を踏んでいく

手順１：まずnpmの再インストールを試みる

ターミナルで　npm install -g npm　を実行するも、再びEACCESエラーが発生

npm ERR! code EACCES
npm ERR! syscall rename
npm ERR! path /usr/local/lib/node_modules/npm
npm ERR! dest /usr/local/lib/node_modules/.npm-i9nnxROI
npm ERR! errno -13
npm ERR! Error: EACCES: permission denied, rename '/usr/local/lib/node_modules/npm' -> '/usr/local/lib/node_modules/.npm-i9nnxROI'
npm ERR!  [Error: EACCES: permission denied, rename '/usr/local/lib/node_modules/npm' -> '/usr/local/lib/node_modules/.npm-i9nnxROI'] {
npm ERR!   errno: -13,
npm ERR!   code: 'EACCES',
npm ERR!   syscall: 'rename',
npm ERR!   path: '/usr/local/lib/node_modules/npm',
npm ERR!   dest: '/usr/local/lib/node_modules/.npm-i9nnxROI'
npm ERR! }
npm ERR! 
npm ERR! The operation was rejected by your operating system.
npm ERR! It is likely you do not have the permissions to access this file as the current user
npm ERR! 
npm ERR! If you believe this might be a permissions issue, please double-check the
npm ERR! permissions of the file and its containing directories, or try running
npm ERR! the command again as root/Administrator.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/<ユーザ名>/.npm/_logs/2021-11-06T23_07_02_519Z-debug.log

手順２：うまくいかなかったのでnpmのデフォルトディレクトリを変える

こちらはWindowsには対応していないので注意

さきほどのnpm公式ドキュメントの「1. Back up your computer.」〜「5.On the command line, update your system variables:...」をやってみる （ちなみに2〜5は、実行しても何も表示されない）

以上を踏まえて、　npm install --global yarn　を実行すると、

added 1 package, and audited 2 packages in 1s

成功！！！