在Mac电脑上安装了一些东西后，结果ssh连不上了，ping ip地址又可以。使用ssh localhost命令老是提示Connection closed by ::1。使用ssh -v localhost，提示：
OpenSSH_6.9p1, LibreSSL 2.1.8
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 21: Applying options for *
debug1: Connecting to localhost [::1] port 22.
debug1: Connection established.
debug1: key_load_public: No such file or directory
debug1: identity file /Users/macbookpro/.ssh/id_rsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/macbookpro/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/macbookpro/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/macbookpro/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/macbookpro/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/macbookpro/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/macbookpro/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/macbookpro/.ssh/id_ed25519-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.9
debug1: Remote protocol version 2.0, remote software version OpenSSH_6.9
debug1: match: OpenSSH_6.9 pat OpenSSH* compat 0x04000000
debug1: Authenticating to localhost:22 as ‘macbookpro‘
debug1: SSH2_MSG_KEXINIT sent
Connection closed by ::1
总是链接不上，只能去看日志，结果提示
error: Permissions 0644 for ‘/etc/ssh/ssh_host_dsa_key‘ are too open. : 31 time(s)
error: Permissions 0644 for ‘/etc/ssh/ssh_host_rsa_key‘ are too open. : 31 time(s)
error: bad permissions: ignore key: /etc/ssh/ssh_host_dsa_key : 31 time(s)
error: It is recommended that your private key files are NOT accessible by others. : 62 time(s)
error: bad permissions: ignore key: /etc/ssh/ssh_host_rsa_key : 31 time(s)
error writing /proc/self/oom_adj: Operation not permitted : 54 time(s)
然后在终端使用命令：‘sudo chmod 600 /etc/ssh/ssh_host_?sa_key‘，终于可以连上了。这里记录一下，防止以后遇到同样的问题。