Permission denied (publickey)

==> Updating Homebrew...
[email protected]: Permission denied (publickey).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

苹果公司更新了其技术说明 ，指出自 10.12.2 版本起，macOS 包含了 OpenSSH 7.3p1 版本及其新行为。通过 ssh-add -K 添加到钥匙串的密钥在重启后不会自动重新添加到 ssh-agent。

方案一，手动执行下面👇的命令：

ssh-add ~/.ssh/userKey

方案二，或者，在 ~/.ssh 下创建 config 文件(推荐使用这个方式。)，内容如下：

Host * (asterisk for all hosts or add specific host)
  AddKeysToAgent yes
  UseKeychain yes
  IdentityFile <key> (e.g. ~/.ssh/userKey)

Ref:

• jirsbek/SSH-keys-in-macOS-Sierra-keychain: Saving SSH keys in macOS Sierra keychain
• Brew update fails with Permission denied (publickey). · Issue #52 · Homebrew/brew
• 错误：权限被拒绝（公钥） - GitHub 文档