加速ssh鏈接的方法（優化ssh服務）

目錄

• 加速ssh鏈接的方法（優化ssh服務）
  • 1、修改 /etc/ssh/sshd_config
  • 2、修改被鏈接端的文件 /etc/nsswitch.conf
  • 3、修改主動鏈接端的 /etc/hosts
  • 4、查看鏈接過程 ssh -v

加速ssh鏈接的方法（優化ssh服務）

本文參考於https://www.cnblogs.com/fwdxl/p/6723820.html，在其基礎上略作整理。

1、修改 /etc/ssh/sshd_config

常常出現ssh鏈接緩慢，讓人誤覺得是ssh鏈接不上。緣由是由於server的sshd會去DNS查找訪問
client IP的hostname，若是DNS不可用或者沒有相關記錄，就會耗費大量時間。

vim /etc/ssh/sshd_config
UseDNS no
GSSAPIAuthentication no
GSSAPICleanupCredentials no

配置文件中[UseDNS yes]被註釋,但默認開關就是yes...(SSH服務默認啓用了DNS反向解析的功能)

2、修改被鏈接端的文件 /etc/nsswitch.conf

hosts： files dns 去掉dns

這行的含義是對於訪問的主機進行域名解析的順序，是先訪問file，也就是/etc/hosts文件，若是hosts中沒有記錄域名，則訪問dns，進行域名解析；若是dns也沒法訪問，就會等待訪問超時後返回，所以等待時間比較長。那若是將這一行屏蔽掉是否是也能夠達到一樣的效果呢？應該是能夠的，可是若是本機要經過域名訪問其餘服務器，則確定沒法訪問，所以這行理論上應該須要保留。這個問題也提示咱們，dns若是不可用，會帶來的一些反作用的。

3、修改主動鏈接端的 /etc/hosts

若是還慢的話，檢查ssh服務端上/etc/hosts文件中，127.0.0.1對應的主機名是否和 uname -n的結果同樣，或者把本機ip和hostname(uname -n結果)加入到/etc/hosts裏。

4、查看鏈接過程 ssh -v

[root@ansible ~]# ssh -v root@192.168.75.136
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 192.168.75.136 [192.168.75.136] port 22.
debug1: Connection established.
debug1: permanently_set_uid: 0/0
debug1: key_load_public: No such file or directory
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_5.3
debug1: match: OpenSSH_5.3 pat OpenSSH_5* compat 0x0c000000
debug1: Authenticating to 192.168.75.136:22 as 'root'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: diffie-hellman-group-exchange-sha256
debug1: kex: host key algorithm: ssh-rsa
debug1: kex: server->client cipher: aes128-ctr MAC: umac-64@openssh.com compression: none
debug1: kex: client->server cipher: aes128-ctr MAC: umac-64@openssh.com compression: none
debug1: kex: diffie-hellman-group-exchange-sha256 need=16 dh_need=16
debug1: kex: diffie-hellman-group-exchange-sha256 need=16 dh_need=16
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<3072<8192) sent
debug1: got SSH2_MSG_KEX_DH_GEX_GROUP
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: got SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Server host key: ssh-rsa SHA256:U+p+ybfgROyI0fCuyLffRhMMBeDIuzR4AdVWfNO7MhY
The authenticity of host '192.168.75.136 (192.168.75.136)' can't be established.
RSA key fingerprint is SHA256:U+p+ybfgROyI0fCuyLffRhMMBeDIuzR4AdVWfNO7MhY.
RSA key fingerprint is MD5:a5:98:06:58:84:35:d3:f4:4c:f8:43:a1:a5:12:f5:8e.
Are you sure you want to continue connecting (yes/no)? yes    保存祕鑰的交互信息
Warning: Permanently added '192.168.75.136' (RSA) to the list of known hosts.
debug1: rekey after 4294967296 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: rekey after 4294967296 blocks
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,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: publickey
debug1: Trying private key: /root/.ssh/id_rsa
debug1: Trying private key: /root/.ssh/id_dsa
debug1: Trying private key: /root/.ssh/id_ecdsa
debug1: Trying private key: /root/.ssh/id_ed25519
debug1: Next authentication method: password
root@192.168.75.136's password:     輸入root用戶登陸密碼
debug1: Authentication succeeded (password).
Authenticated to 192.168.75.136 ([192.168.75.136]:22).
debug1: channel 0: new [client-session]
debug1: Requesting no-more-sessions@openssh.com
debug1: Entering interactive session.
debug1: pledge: network
debug1: Sending environment.
debug1: Sending env LANG = en_US.UTF-8
Last login: Tue Jun 18 22:35:15 2019 from 192.168.75.145