git fetch fatal: Permission denied (publickey,password).

git fetch origin branchName 报错：

Permission denied (publickey,password).
fatal: Could not read from remote repository.

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

原因是没有设置 ssh key

三步解决：

1、生成 ssh key

1. cd ~/.ssh
2. ssh-keygen -t rsa -b 2048 -C "你的邮箱"
3. Enter file in which to save the key (Users/username/.ssh/id_rsa): 这步提示输入文件名称，直接回车表示默认文件名id_rsa，可以自定义文件名，如 custom_id_rsa 
4. Enter passphrase (empty for no passphrase):输入密码，可以为空
5. 提示再次确认密码
6. 完成，拷贝 id_rsa.pub 的内容进行下一步

2、拷贝 id_rsa.pub 的内容添加到 gitlab 的 Settings - “SSH Keys” 中

3、本地添加 ssh 秘钥

ssh-add id_rsa

Identity added: id_rsa (xxx@xxx.cn)

再次执行 git fetch origin branchName 成功.