linux – 为什么SSHD挂在“服务器接受密钥”

我使用公钥认证一年来一直没有问题.

没有对客户端或服务器的ssh配置进行任何更改.现在,ssh连接永远不会完成或失败,它们只是挂起.以下是尝试连接时的调试输出：

OpenSSH_6.0p1 Debian-3ubuntu1,OpenSSL 1.0.1c 10 May 2012
debug1: Reading configuration data /home/jivan/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to <host> [<ip>] port <port>.
debug1: Connection established.
debug1: identity file .ssh/id_rsa.pub type 1
debug1: Checking blacklist file /usr/share/ssh/blacklist.RSA-2048
debug1: Checking blacklist file /etc/ssh/blacklist.RSA-2048
debug1: identity file .ssh/id_rsa.pub-cert type -1
debug1: Remote protocol version 2.0,remote software version OpenSSH_5.8p1 Debian-7ubuntu1
debug1: match: OpenSSH_5.8p1 Debian-7ubuntu1 pat OpenSSH_5*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.0p1 Debian-3ubuntu1
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-md5 none
debug1: kex: client->server aes128-ctr hmac-md5 none
debug1: sending SSH2_MSG_KEX_ECDH_INIT
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ECDSA 81:63:05:0c:39:6b:77:d7:a2:25:93:30:80:f1:ba:0e
debug1: Host '[<host>]:<port>' is known and matches the ECDSA host key.
debug1: Found key in /home/jivan/.ssh/known_hosts:39
debug1: ssh_ecdsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
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: .ssh/id_rsa.pub
debug1: Server accepts key: pkalg ssh-rsa blen 279

服务器日志：

Feb 24 12:02:38 balance sshd[5734]: debug1: Forked child 6745.
Feb 24 12:02:38 balance sshd[6745]: Set /proc/self/oom_score_adj to 0
Feb 24 12:02:38 balance sshd[6745]: debug1: rexec start in 5 out 5 newsock 5 pip
e 7 sock 8
Feb 24 12:02:38 balance sshd[6745]: debug1: inetd sockets after dupping: 3,3
Feb 24 12:02:38 balance sshd[6745]: Connection from 207.204.228.55 port 57967
Feb 24 12:02:38 balance sshd[6745]: debug1: Client protocol version 2.0; client 
software version OpenSSH_6.0p1 Debian-3ubuntu1
Feb 24 12:02:38 balance sshd[6745]: debug1: match: OpenSSH_6.0p1 Debian-3ubuntu1
 pat OpenSSH*
Feb 24 12:02:38 balance sshd[6745]: debug1: Enabling compatibility mode for prot
ocol 2.0
Feb 24 12:02:38 balance sshd[6745]: debug1: Local version string SSH-2.0-OpenSSH_5.8p1 Debian-7ubuntu1
Feb 24 12:02:39 balance sshd[6745]: debug1: PAM: initializing for "jivan"
Feb 24 12:02:39 balance sshd[6745]: debug1: PAM: setting PAM_RHOST to "207.204.228.55"
Feb 24 12:02:39 balance sshd[6745]: debug1: PAM: setting PAM_TTY to "ssh"
Feb 24 12:02:40 balance sshd[6745]: debug1: Checking blacklist file /usr/share/ssh/blacklist.RSA-2048
Feb 24 12:02:40 balance sshd[6745]: debug1: Checking blacklist file /etc/ssh/blacklist.RSA-2048
Feb 24 12:02:40 balance sshd[6745]: debug1: temporarily_use_uid: 1000/1000 (e=0/0)
Feb 24 12:02:40 balance sshd[6745]: debug1: trying public key file /home/jivan/.ssh/authorized_keys
Feb 24 12:02:40 balance sshd[6745]: debug1: fd 4 clearing O_NONBLOCK
Feb 24 12:02:40 balance sshd[6745]: debug1: matching key found: file /home/jivan/.ssh/authorized_keys,line 1
Feb 24 12:02:40 balance sshd[6745]: Found matching RSA key: 5f:8c:76:ad:48:6a:f5:73:03:6a:36:13:c0:ea:3b:45
Feb 24 12:02:40 balance sshd[6745]: debug1: restore_uid: 0/0

任何想法可能是什么问题？

更新：
问题在开始时神秘地停止了.仍然对可能导致这种情况的任何见解感兴趣.

解决方法

这通常是由反向DNS问题引起的;这一周发生在我的旧服务器上.你是正确的调用sshd -d,但反向DNS问题不会真正变得明显,除非你用sshd -ddd运行它,以便你看到debug3的输出.

虽然反向DNS问题并不总是导致事情严重失败,但如果与连接尝试相关的足够DNS查找失败(即所有DNS服务器完全不可用,或者相关区域/反向区域足够超时),在某些配置下,完全锁定对系统的ssh访问就足够了.如果服务器不耐烦并丢弃连接,则设置客户端超时的高低并不重要.