在 Ubuntu 上緩慢連接 ssh

我最近在我的桌面上安裝了 Ubuntu 10.10 作為第二個作業系統，但我遇到了一個奇怪的問題：通過 ssh 連接到其他 linux 機器需要幾十秒。在 Windows 上，我沒有這樣的問題，它立即連接。

所以，同樣，這不是主機的問題（即高負載），也沒有連接問題（即高延遲、丟包等）。問題肯定與客戶端及其在連接時執行的操作有關。

我懷疑這與 DNS/反向 DNS 有關。就像在連接之前等待在我的 IP 上獲得反向 DNS 一樣，我不知道..

有誰知道如何解決這一問題？謝謝。

稍後編輯：正如 Janne 建議的那樣，我使用 -vvv 參數執行命令。輸出是：

ssh -p 6969 -vvv myuser@myserver.mydomain.com
OpenSSH_5.5p1 Debian-4ubuntu4, OpenSSL 0.9.8o 01 Jun 2010
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug2: ssh_connect: needpriv 0
debug1: Connecting to myserver.mydomain.com [178.21.120.198] port 6969.
debug1: Connection established.
debug1: identity file /home/sorin/.ssh/id_rsa type -1
debug1: identity file /home/sorin/.ssh/id_rsa-cert type -1
debug1: identity file /home/sorin/.ssh/id_dsa type -1
debug1: identity file /home/sorin/.ssh/id_dsa-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_4.3
debug1: match: OpenSSH_4.3 pat OpenSSH_4*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.5p1 Debian-4ubuntu4
debug2: fd 3 setting O_NONBLOCK
debug1: SSH2_MSG_KEXINIT sent
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-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-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,umac-64@openssh.com,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-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
debug2: kex_parse_kexinit: ssh-rsa,ssh-dss
debug2: kex_parse_kexinit: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,arcfour256,arcfour,aes192-cbc,aes256-cbc,rijndael-cbc@lysator.liu.se,aes128-ctr,aes192-ctr,aes256-ctr
debug2: kex_parse_kexinit: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,arcfour256,arcfour,aes192-cbc,aes256-cbc,rijndael-cbc@lysator.liu.se,aes128-ctr,aes192-ctr,aes256-ctr
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,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
debug2: dh_gen_key: priv key bits set: 111/256
debug2: bits set: 534/1024
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug3: put_host_port: [178.21.120.198]:6969
debug3: put_host_port: [myserver.mydomain.com]:6969
debug3: check_host_in_hostfile: host [myserver.mydomain.com]:6969 filename /home/sorin/.ssh/known_hosts
debug3: check_host_in_hostfile: host [myserver.mydomain.com]:6969 filename /home/sorin/.ssh/known_hosts
debug3: check_host_in_hostfile: match line 1
debug3: check_host_in_hostfile: host [178.21.120.198]:6969 filename /home/sorin/.ssh/known_hosts
debug3: check_host_in_hostfile: host [178.21.120.198]:6969 filename /home/sorin/.ssh/known_hosts
debug3: check_host_in_hostfile: match line 2
debug1: Host '[myserver.mydomain.com]:6969' is known and matches the RSA host key.
debug1: Found key in /home/sorin/.ssh/known_hosts:1
debug2: bits set: 491/1024
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
debug2: set_newkeys: mode 0
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug2: service_accept: ssh-userauth
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug2: key: /home/sorin/.ssh/id_rsa ((nil))
debug2: key: /home/sorin/.ssh/id_dsa ((nil))
debug1: Authentications that can continue: publickey,gssapi-with-mic,password
debug3: start over, passed a different list publickey,gssapi-with-mic,password
debug3: preferred gssapi-keyex,gssapi-with-mic,publickey,keyboard-interactive,password
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
debug1: Unspecified GSS failure.  Minor code may provide more information
Credentials cache file '/tmp/krb5cc_1000' not found

debug1: Unspecified GSS failure.  Minor code may provide more information
Credentials cache file '/tmp/krb5cc_1000' not found

debug1: Unspecified GSS failure.  Minor code may provide more information


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: /home/sorin/.ssh/id_rsa
debug3: no such identity: /home/sorin/.ssh/id_rsa
debug1: Trying private key: /home/sorin/.ssh/id_dsa
debug3: no such identity: /home/sorin/.ssh/id_dsa
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
myuser@myserver.mydomain.com's password:

出於安全原因，我已將使用者替換為 myuser，並將伺服器名稱替換為 myserver.mydomain.com。

嘗試在 sshd_config 和 ssh_config 中將 UseDNS 設置為“no”。還將 GSSAPIAuthentication 設置為 no。

哪一步慢？GSS 認證？您可以通過安裝 moreutils 並執行來為我們提供時間戳

ssh -vvv user@host 2> >(ts)

您可以使用此標誌跳過 GSSAPI：

-o PreferredAuthentications=hostbased,publickey,keyboard-interactive,password

引用自：https://serverfault.com/questions/201073