ssh 登录很慢该如何解决
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2022-06-28 20:20:57
ssh登录很慢解决方法
使用ssh客户端（如：）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...
ssh登录很慢解决方法
使用ssh客户端（如：）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
vi /etc/ssh/sshd_config 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：
debug1: next authentication method: gssapi-with-mic 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
vi /etc/ssh/ssh_config 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
[root@192-168-3-40 ~]# ssh -vvv root@192.168.3.44 openssh_5.3p1, openssl 1.0.1e-fips 11 feb 2013 debug1: reading configuration data /etc/ssh/ssh_config debug1: applying options for * debug2: ssh_connect: needpriv 0 debug1: connecting to 192.168.3.44 [192.168.3.44] port 22. debug1: connection established. debug1: permanently_set_uid: 0/0 debug1: identity file /root/.ssh/identity type -1 debug1: identity file /root/.ssh/identity-cert type -1 debug1: identity file /root/.ssh/id_rsa type -1 debug1: identity file /root/.ssh/id_rsa-cert type -1 debug1: identity file /root/.ssh/id_dsa type -1 debug1: identity file /root/.ssh/id_dsa-cert type -1 debug1: identity file /root/.ssh/id_ecdsa type -1 debug1: identity file /root/.ssh/id_ecdsa-cert type -1 debug1: remote protocol version 2.0, remote software version openssh_5.3 debug1: match: openssh_5.3 pat openssh* debug1: enabling compatibility mode for protocol 2.0 debug1: local version string ssh-2.0-openssh_5.3 debug2: fd 3 setting o_nonblock debug1: ssh2_msg_kexinit sent debug3: wrote 960 bytes for a total of 981 debug1: ssh2_msg_kexinit received debug2: kex_parse_kexinit: diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1 debug2: kex_parse_kexinit: ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,ssh-rsa,ssh-dss 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,rijndael-cbc@lysator.liu.se 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,rijndael-cbc@lysator.liu.se debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96 debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96 debug2: kex_parse_kexinit: none,zlib@openssh.com,zlib debug2: kex_parse_kexinit: none,zlib@openssh.com,zlib debug2: kex_parse_kexinit: debug2: kex_parse_kexinit: debug2: kex_parse_kexinit: first_kex_follows 0 debug2: kex_parse_kexinit: reserved 0 debug2: kex_parse_kexinit: diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1 debug2: kex_parse_kexinit: ssh-rsa,ssh-dss 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,rijndael-cbc@lysator.liu.se 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,rijndael-cbc@lysator.liu.se debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96 debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96 debug2: kex_parse_kexinit: none,zlib@openssh.com debug2: kex_parse_kexinit: none,zlib@openssh.com debug2: kex_parse_kexinit: debug2: kex_parse_kexinit: debug2: kex_parse_kexinit: first_kex_follows 0 debug2: kex_parse_kexinit: reserved 0 debug2: mac_setup: found hmac-md5 debug1: kex: server->client aes128-ctr hmac-md5 none debug2: mac_setup: found hmac-md5 debug1: kex: client->server aes128-ctr hmac-md5 none debug1: ssh2_msg_kex_dh_gex_request(1024<1024<8192) sent debug1: expecting ssh2_msg_kex_dh_gex_group debug3: wrote 24 bytes for a total of 1005 debug2: dh_gen_key: priv key bits set: 120/256 debug2: bits set: 506/1024 debug1: ssh2_msg_kex_dh_gex_init sent debug1: expecting ssh2_msg_kex_dh_gex_reply debug3: wrote 144 bytes for a total of 1149 debug3: check_host_in_hostfile: host 192.168.3.44 filename /root/.ssh/known_hosts debug3: check_host_in_hostfile: host 192.168.3.44 filename /root/.ssh/known_hosts debug3: check_host_in_hostfile: match line 8 debug1: host '192.168.3.44' is known and matches the rsa host key. debug1: found key in /root/.ssh/known_hosts:8 debug2: bits set: 527/1024 debug1: ssh_rsa_verify: signature correct debug2: kex_derive_keys debug2: set_newkeys: mode 1 debug1: ssh2_msg_newkeys sent debug1: expecting ssh2_msg_newkeys debug3: wrote 16 bytes for a total of 1165 debug2: set_newkeys: mode 0 debug1: ssh2_msg_newkeys received debug1: ssh2_msg_service_request sent debug3: wrote 48 bytes for a total of 1213 debug2: service_accept: ssh-userauth debug1: ssh2_msg_service_accept received debug2: key: /root/.ssh/identity ((nil)) debug2: key: /root/.ssh/id_rsa ((nil)) debug2: key: /root/.ssh/id_dsa ((nil)) debug2: key: /root/.ssh/id_ecdsa ((nil)) debug3: wrote 64 bytes for a total of 1277 debug1: authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password debug3: start over, passed a different list publickey,gssapi-keyex,gssapi-with-mic,password debug3: preferred gssapi-keyex,gssapi-with-mic,publickey,keyboard-interactive,password debug3: authmethod_lookup gssapi-keyex debug3: remaining preferred: gssapi-with-mic,publickey,keyboard-interactive,password debug3: authmethod_is_enabled gssapi-keyex debug1: next authentication method: gssapi-keyex debug1: no valid key exchange context debug2: we did not send a packet, disable method debug3: authmethod_lookup gssapi-with-mic debug3: remaining preferred: publickey,keyboard-interactive,password debug3: authmethod_is_enabled gssapi-with-mic debug1: next authentication method: gssapi-with-mic debug3: trying to reverse map address 192.168.3.44. debug1: unspecified gss failure. minor code may provide more information cannot determine realm for numeric host address debug1: unspecified gss failure. minor code may provide more information cannot determine realm for numeric host address debug1: unspecified gss failure. minor code may provide more information debug1: unspecified gss failure. minor code may provide more information cannot determine realm for numeric host address debug2: we did not send a packet, disable method debug3: authmethod_lookup publickey debug3: remaining preferred: keyboard-interactive,password debug3: authmethod_is_enabled publickey debug1: next authentication method: publickey debug1: trying private key: /root/.ssh/identity debug3: no such identity: /root/.ssh/identity debug1: trying private key: /root/.ssh/id_rsa debug3: no such identity: /root/.ssh/id_rsa debug1: trying private key: /root/.ssh/id_dsa debug3: no such identity: /root/.ssh/id_dsa debug1: trying private key: /root/.ssh/id_ecdsa debug3: no such identity: /root/.ssh/id_ecdsa debug2: we did not send a packet, disable method debug3: authmethod_lookup password debug3: remaining preferred: ,password debug3: authmethod_is_enabled password debug1: next authentication method: password root@192.168.3.44's password:
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