前言
本来要在服务器上安装docker-machine，然后管理其他云服务器的docker容器的，结果到了ssh免密登录这一步，一直走不通。下面把我遇到的问题，记录下。
注：docker-machine安装可参考文章：https://blog.csdn.net/wfs1994/article/details/80658555
ssh免密登录
由于，要管理其他的云服务器的docker，所以需要用ssh免密登录到其余的云服务器（主服务器192.168.20.200，远程服务器192.168.20.201）。如下：
ssh-keygen -t rsa
ssh-copy-id 192.168.20.201
然后输入192.168.20.201的密码，提示ok了，于是测试下
ssh 192.168.20.201
结果还是需要输入密码。
google一下
出现这种奇葩问题，果断，先google一下。结果大部分都说是权限问题，然后我按照教程说的修改了192.168.20.201下root目录及下面的.ssh文件夹的权限，还是不行。
于是用ssh -v 192.168.20.201看一下日志：
OpenSSH_7.4p1, OpenSSL 1.0.2k-fips 26 Jan 2017
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 58: Applying options for *
debug1: Connecting to 192.168.20.201 [192.168.20.201] port 22.
debug1: Connection established.
debug1: permanently_set_uid: 0/0
debug1: identity file /root/.ssh/id_rsa type 1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ed25519-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.4
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.4
debug1: match: OpenSSH_7.4 pat OpenSSH* compat 0x04000000
debug1: Authenticating to 192.168.20.201:22 as 'root'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: curve25519-sha256
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: [email protected] MAC: <implicit> compression: none
debug1: kex: client->server cipher: [email protected] MAC: <implicit> compression: none
debug1: kex: curve25519-sha256 need=64 dh_need=64
debug1: kex: curve25519-sha256 need=64 dh_need=64
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:wORn5yWtd8wO3XfFm11Wu6iNezHNRT5QKxowGHZyCT0
debug1: Host '192.168.20.201' is known and matches the ECDSA host key.
debug1: Found key in /root/.ssh/known_hosts:1
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=<rsa-sha2-256,rsa-sha2-512>
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: gssapi-keyex,gssapi-with-mic,password
debug1: Next authentication method: gssapi-keyex
debug1: No valid Key exchange context
debug1: Next authentication method: gssapi-with-mic
debug1: Unspecified GSS failure. Minor code may provide more information
No Kerberos credentials available (default cache: KEYRING:persistent:0)
debug1: Unspecified GSS failure. Minor code may provide more information
No Kerberos credentials available (default cache: KEYRING:persistent:0)
debug1: Next authentication method: password发现ssh确实是几种认证方式都失败了，直接到了需要密码登录，如下：
那这是什么原因造成的呢？
结果发现认证方式只有gssapi-keyex,gssapi-with-mic,password，并没有publickey。
那肯定是192.168.20.201这台服务器上的sshd配置有问题。
于是登录192.168.20.201这台服务器，看了下sshd配置
搜索PubkeyAuthentication，结果发现这项被注释了。放开注释，重启sshd：service sshd restart。
再用ssh远程登录这台服务器，ok了。