linux下ssh链接慢的缘由调查及解决方案

项目中的一台阿里云，最近一段时间出现ssh的时候，链接很是慢，大概输入密码后要10-20秒左右才能连上，如下记录调查过程及解决办法

经过网上的一些查询，发现大都是由于设置dns，hosts或者经过关闭UseDNS=no GSSAPIAuthentication no的方式来解决，但个人问题和这些不一样，首先我是经过ip链接的，不存在dns域名解析的问题，而且sshd_config文件中的这些设置项也都是no，所以本身经过调查，发现是如下缘由引发的：

---

 

1.经过[-v]参数，查看ssh链接的具体过程

deMacBook-Pro:~ yyq$ ssh -v root@x.x.x.x -p xx
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 x.x.x.x [x.x.x.x] port xx.
debug1: Connection established.
debug1: identity file /Users/yyq/.ssh/id_rsa type 1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/yyq/.ssh/id_rsa-cert type -1
debug1: identity file /Users/yyq/.ssh/id_dsa type 2
debug1: key_load_public: No such file or directory
debug1: identity file /Users/yyq/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/yyq/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/yyq/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/yyq/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/yyq/.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_7.2p2 Ubuntu-4ubuntu2.1
debug1: match: OpenSSH_7.2p2 Ubuntu-4ubuntu2.1 pat OpenSSH* compat 0x04000000
debug1: Authenticating to x.x.x.x:xx as 'root'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client chacha20-poly1305@openssh.com <implicit> none
debug1: kex: client->server chacha20-poly1305@openssh.com <implicit> none
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:HictrRpAs7Yv495dDLNqHsFCNKXVACpX9FWUnNVenZU
debug1: Host '[x.x.x.x]:xx' is known and matches the ECDSA host key.
debug1: Found key in /Users/yyq/.ssh/known_hosts:38
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,password
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /Users/yyq/.ssh/id_rsa
debug1: Authentications that can continue: publickey,password
debug1: Offering DSA public key: /Users/yyq/.ssh/id_dsa
debug1: Authentications that can continue: publickey,password
debug1: Trying private key: /Users/yyq/.ssh/id_ecdsa
debug1: Trying private key: /Users/yyq/.ssh/id_ed25519
debug1: Next authentication method: password
root@x.x.x.x's password:

 

首先观察在要求输入密码前有没有出现耗时的操做？
个人问题并无，所以，继续输出密码：

root@x.x.x.x's password: 
debug1: Authentication succeeded (password).
Authenticated to x.x.x.x ([x.x.x.x]:xx).
debug1: channel 0: new [client-session]
debug1: Requesting no-more-sessions@openssh.com
debug1: Entering interactive session.

 输入密码后，发现停在这里了，大概10-20秒后，就能够链接上；

经过日志能够发现，密码的验证没有损耗时间，已经正确验证经过Authentication succeeded (password)
哪么究竟是什么缘由致使的速度这么慢？

2.打开服务器的系统日志，查看

tail -f /var/log/auth.log
sshd[12642]: pam_systemd(sshd:session): Failed to create session: Connection timed out
dbus[617]: [system] Failed to activate service 'org.freedesktop.login1': timed out
sshd[12642]: Received disconnect from x.x.x.x port 52856:11: disconnected by user
sshd[12642]: Disconnected from x.x.x.x port 52856
sshd[12642]: pam_unix(sshd:session): session closed for user root
sshd[12689]: userauth_pubkey: key type ssh-dss not in PubkeyAcceptedKeyTypes [preauth]
sshd[12689]: Accepted password for root from x.x.x.x port 52866 ssh2
sshd[12689]: pam_unix(sshd:session): session opened for user root by (uid=0)
sshd[12689]: pam_systemd(sshd:session): Failed to create session: Connection timed out
dbus[617]: [system] Failed to activate service 'org.freedesktop.login1': timed out

 从日志中能够看到[system] Failed to activate service 'org.freedesktop.login1': timed out

的错误，查了下资料，大体意思以下：
dbus的服务重启后，systemd-logind服务没有重启致使，能够查看systemctl status systemd-logind的状态，解决方法就是重启该服务 systemctl restart systemd-logind
重启systemd-logind服务后，发现ssh能够秒链接了