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ssh登录很慢解决方法

使用ssh客户端（如：putty）连接Linux服务器，可能会等待10-30秒才有提示输入密码。严重影响工作效率。登录很慢，登录上去后速度正常，这种情况主要有两种可能的原因：

1. DNS反向解析问题

OpenSSH在用户登录的时候会验证IP，它根据用户的IP使用反向DNS找到主机名，再使用DNS找到IP地址，最后匹配一下登录的IP是否合法。如果客户机的IP没有域名，或者DNS服务器很慢或不通，那么登录就会很花时间。

解决办法：在目标服务器上修改sshd服务器端配置,并重启sshd

  1. vi /etc/ssh/sshd_config
  2. UseDNS no

2. 关闭ssh的gssapi认证

用ssh -v user@server 可以看到登录时有如下信息：

  1. debug1: Next authentication method: gssapi-with-mic
  2. debug1: Unspecified GSS failure. Minor code may provide more information

注：ssh -vvv user@server 可以看到更细的debug信息

解决办法：

修改sshd服务器端配置

  1. vi /etc/ssh/ssh_config
  2. GSSAPIAuthentication no

可以使用ssh -o GSSAPIAuthentication=no user@server登录

GSSAPI ( Generic Security Services Application Programming Interface) 是一套类似Kerberos 5的通用网络安全系统接口。该接口是对各种不同的客户端服务器安全机制的封装，以消除安全接口的不同，降低编程难度。但该接口在目标机器无域名解析时会有 问题

使用strace查看后发现，ssh在验证完key之后，进行authentication gssapi-with-mic，此时先去连接DNS服务器，在这之后会进行其他操作

  1. [root@192-168-3-40 ~]# ssh -vvv [email protected]
  2. OpenSSH_5.3p1, OpenSSL 1.0.1e-fips 11 Feb 2013
  3. debug1: Reading configuration data /etc/ssh/ssh_config
  4. debug1: Applying options for *
  5. debug2: ssh_connect: needpriv 0
  6. debug1: Connecting to 192.168.3.44 [192.168.3.44] port 22.
  7. debug1: Connection established.
  8. debug1: permanently_set_uid: 0/0
  9. debug1: identity file /root/.ssh/identity type -1
  10. debug1: identity file /root/.ssh/identity-cert type -1
  11. debug1: identity file /root/.ssh/id_rsa type -1
  12. debug1: identity file /root/.ssh/id_rsa-cert type -1
  13. debug1: identity file /root/.ssh/id_dsa type -1
  14. debug1: identity file /root/.ssh/id_dsa-cert type -1
  15. debug1: identity file /root/.ssh/id_ecdsa type -1
  16. debug1: identity file /root/.ssh/id_ecdsa-cert type -1
  17. debug1: Remote protocol version 2.0, remote software version OpenSSH_5.3
  18. debug1: match: OpenSSH_5.3 pat OpenSSH*
  19. debug1: Enabling compatibility mode for protocol 2.0
  20. debug1: Local version string SSH-2.0-OpenSSH_5.3
  21. debug2: fd 3 setting O_NONBLOCK
  22. debug1: SSH2_MSG_KEXINIT sent
  23. debug3: Wrote 960 bytes for a total of 981
  24. debug1: SSH2_MSG_KEXINIT received
  25. debug2: kex_parse_kexinit: diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
  26. debug2: kex_parse_kexinit: [email protected],[email protected],[email protected],[email protected],ssh-rsa,ssh-dss
  27. debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,[email protected]
  28. debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,[email protected]
  29. debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
  30. debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
  31. debug2: kex_parse_kexinit: none,[email protected],zlib
  32. debug2: kex_parse_kexinit: none,[email protected],zlib
  33. debug2: kex_parse_kexinit:
  34. debug2: kex_parse_kexinit:
  35. debug2: kex_parse_kexinit: first_kex_follows 0
  36. debug2: kex_parse_kexinit: reserved 0
  37. debug2: kex_parse_kexinit: diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
  38. debug2: kex_parse_kexinit: ssh-rsa,ssh-dss
  39. debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,[email protected]
  40. debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,[email protected]
  41. debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
  42. debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
  43. debug2: kex_parse_kexinit: none,[email protected]
  44. debug2: kex_parse_kexinit: none,[email protected]
  45. debug2: kex_parse_kexinit:
  46. debug2: kex_parse_kexinit:
  47. debug2: kex_parse_kexinit: first_kex_follows 0
  48. debug2: kex_parse_kexinit: reserved 0
  49. debug2: mac_setup: found hmac-md5
  50. debug1: kex: server->client aes128-ctr hmac-md5 none
  51. debug2: mac_setup: found hmac-md5
  52. debug1: kex: client->server aes128-ctr hmac-md5 none
  53. debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
  54. debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
  55. debug3: Wrote 24 bytes for a total of 1005
  56. debug2: dh_gen_key: priv key bits set: 120/256
  57. debug2: bits set: 506/1024
  58. debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
  59. debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
  60. debug3: Wrote 144 bytes for a total of 1149
  61. debug3: check_host_in_hostfile: host 192.168.3.44 filename /root/.ssh/known_hosts
  62. debug3: check_host_in_hostfile: host 192.168.3.44 filename /root/.ssh/known_hosts
  63. debug3: check_host_in_hostfile: match line 8
  64. debug1: Host '192.168.3.44' is known and matches the RSA host key.
  65. debug1: Found key in /root/.ssh/known_hosts:8
  66. debug2: bits set: 527/1024
  67. debug1: ssh_rsa_verify: signature correct
  68. debug2: kex_derive_keys
  69. debug2: set_newkeys: mode 1
  70. debug1: SSH2_MSG_NEWKEYS sent
  71. debug1: expecting SSH2_MSG_NEWKEYS
  72. debug3: Wrote 16 bytes for a total of 1165
  73. debug2: set_newkeys: mode 0
  74. debug1: SSH2_MSG_NEWKEYS received
  75. debug1: SSH2_MSG_SERVICE_REQUEST sent
  76. debug3: Wrote 48 bytes for a total of 1213
  77. debug2: service_accept: ssh-userauth
  78. debug1: SSH2_MSG_SERVICE_ACCEPT received
  79. debug2: key: /root/.ssh/identity ((nil))
  80. debug2: key: /root/.ssh/id_rsa ((nil))
  81. debug2: key: /root/.ssh/id_dsa ((nil))
  82. debug2: key: /root/.ssh/id_ecdsa ((nil))
  83. debug3: Wrote 64 bytes for a total of 1277
  84. debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password
  85. debug3: start over, passed a different list publickey,gssapi-keyex,gssapi-with-mic,password
  86. debug3: preferred gssapi-keyex,gssapi-with-mic,publickey,keyboard-interactive,password
  87. debug3: authmethod_lookup gssapi-keyex
  88. debug3: remaining preferred: gssapi-with-mic,publickey,keyboard-interactive,password
  89. debug3: authmethod_is_enabled gssapi-keyex
  90. debug1: Next authentication method: gssapi-keyex
  91. debug1: No valid Key exchange context
  92. debug2: we did not send a packet, disable method
  93. debug3: authmethod_lookup gssapi-with-mic
  94. debug3: remaining preferred: publickey,keyboard-interactive,password
  95. debug3: authmethod_is_enabled gssapi-with-mic
  96. debug1: Next authentication method: gssapi-with-mic
  97. debug3: Trying to reverse map address 192.168.3.44.
  98. debug1: Unspecified GSS failure.  Minor code may provide more information
  99. Cannot determine realm for numeric host address
  100. debug1: Unspecified GSS failure.  Minor code may provide more information
  101. Cannot determine realm for numeric host address
  102. debug1: Unspecified GSS failure.  Minor code may provide more information
  103. debug1: Unspecified GSS failure.  Minor code may provide more information
  104. Cannot determine realm for numeric host address
  105. debug2: we did not send a packet, disable method
  106. debug3: authmethod_lookup publickey
  107. debug3: remaining preferred: keyboard-interactive,password
  108. debug3: authmethod_is_enabled publickey
  109. debug1: Next authentication method: publickey
  110. debug1: Trying private key: /root/.ssh/identity
  111. debug3: no such identity: /root/.ssh/identity
  112. debug1: Trying private key: /root/.ssh/id_rsa
  113. debug3: no such identity: /root/.ssh/id_rsa
  114. debug1: Trying private key: /root/.ssh/id_dsa
  115. debug3: no such identity: /root/.ssh/id_dsa
  116. debug1: Trying private key: /root/.ssh/id_ecdsa
  117. debug3: no such identity: /root/.ssh/id_ecdsa
  118. debug2: we did not send a packet, disable method
  119. debug3: authmethod_lookup password
  120. debug3: remaining preferred: ,password
  121. debug3: authmethod_is_enabled password
  122. debug1: Next authentication method: password
  123. [email protected]'s password:

转载于https://blog.linuxeye.com/420.html

05-11 11:31
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