linux下ssh連線慢的原因調查及解決方案

專案中的一台阿里雲，最近一段時間出現ssh的時候，連線非常慢，大概輸入密碼後要10-20秒左右才能連上，以下記錄調查過程及解決辦法

通過網上的一些查詢，發現大都是因為設定dns，hosts或者通過關閉usedns=no gssapiauthentication no的方式來解決，但我的問題和這些不同，首先我是通過ip連線的，不存在dns網域名稱解析的問題，並且sshd_config檔案中的這些設定項也都是no，因此自己通過調查，發現是以下原因引起的：

1.通過[-v]引數，檢視ssh連線的具體過程

demacbook-pro:~ yyq$ ssh -v [email protected] -p xx
openssh_6.9p1, libressl 2.1.8
debug1: reading configuration data /etc/ssh/ssh_config
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 [email protected] none
debug1: kex: client->server [email protected] 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
[email protected]'s password:

首先觀察在要求輸入密碼前有沒有出現耗時的操作？

我的問題並沒有，因此，繼續輸出密碼：

[email protected]'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 [email protected]
debug1: entering interactive session.

輸入密碼後，發現停在這裡了，大概10-20秒後，就可以連線上；

通過日誌可以發現，密碼的驗證沒有損耗時間，已經正確驗證通過authentication succeeded (password)

哪麼到底是什麼原因導致的速度這麼慢？

2.開啟伺服器的系統日誌，檢視

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

從日誌中可以看到[system] failed to activate service 'org.freedesktop.login1': timed out

的錯誤，查了下資料，大致意思如下：

dbus的服務重啟後，systemd-logind服務沒有重啟導致，可以檢視systemctl status systemd-logind的狀態，解決方法就是重啟該服務 systemctl restart systemd-logind

重啟systemd-logind服務後，發現ssh可以秒連線了

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