SSH 新连接在 Ubuntu 13.04 服务器上开始挂起（不是拒绝或终止）一天左右

Question

最近我们将服务器从 12.04 LTS 服务器升级到 13.04。一切都很好，包括重新启动后。随着所有软件包的更新，我们开始看到一个奇怪的问题，ssh 工作了一天左右（时间不清楚）然后稍后对 SSH 的请求挂起（无法 ctrl+c，什么都没有）。

它已启动并为网络服务器流量等提供服务。

端口 22 是开放的（ips 等稍作修改以便发布）：

nmap -T4 -A x.acme.com

Starting Nmap 6.40 ( http://nmap.org ) at 2013-09-12 16:01 CDT
Nmap scan report for x.acme.com (69.137.56.18)
Host is up (0.026s latency).
rDNS record for 69.137.56.18: c-69-137-56-18.hsd1.tn.provider.net
Not shown: 998 filtered ports
PORT   STATE SERVICE VERSION
22/tcp open  ssh     OpenSSH 6.1p1 Debian 4 (protocol 2.0)
| ssh-hostkey: 1024 54:d3:e3:38:44:f4:20:a4:e7:42:49:d0:a7:f1:3e:21 (DSA)
| 2048 dc:21:77:3b:f4:4e:74:d0:87:33:14:40:04:68:33:a6 (RSA)
|_256 45:69:10:79:5a:9f:0b:f0:66:15:39:87:b9:a1:37:f7 (ECDSA)
80/tcp open  http    Jetty 7.6.2.v20120308
| http-title: Log in as a Bamboo user - Atlassian Bamboo
|_Requested resource was http://x.acme.com/userlogin!default.action;jsessionid=19v135zn8cl1tgso28fse4d50?os_destination=%2Fstart.action
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

Service detection performed. Please report any incorrect results at http://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 12.89 seconds

这是 ssh -vvv：

ssh -vvv x.acme.com
OpenSSH_5.9p1, OpenSSL 0.9.8x 10 May 2012
debug1: Reading configuration data /Users/tfergeson/.ssh/config
debug1: Reading configuration data /etc/ssh_config
debug1: /etc/ssh_config line 20: Applying options for *
debug2: ssh_connect: needpriv 0
debug1: Connecting to x.acme.com [69.137.56.18] port 22.
debug1: Connection established.
debug3: Incorrect RSA1 identifier
debug3: Could not load "/Users/tfergeson/.ssh/id_rsa" as a RSA1 public key
debug1: identity file /Users/tfergeson/.ssh/id_rsa type 1
debug1: identity file /Users/tfergeson/.ssh/id_rsa-cert type -1
debug1: identity file /Users/tfergeson/.ssh/id_dsa type -1
debug1: identity file /Users/tfergeson/.ssh/id_dsa-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_6.1p1 Debian-4
debug1: match: OpenSSH_6.1p1 Debian-4 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.9
debug2: fd 3 setting O_NONBLOCK
debug3: load_hostkeys: loading entries for host "x.acme.com" from file "/Users/tfergeson/.ssh/known_hosts"
debug3: load_hostkeys: found key type RSA in file /Users/tfergeson/.ssh/known_hosts:10
debug3: load_hostkeys: loaded 1 keys
debug3: order_hostkeyalgs: prefer hostkeyalgs: ssh-rsa-cert-v01@openssh.com,ssh-rsa-cert-v00@openssh.com,ssh-rsa
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-v01@openssh.com,ssh-rsa-cert-v00@openssh.com,ssh-rsa,ssh-dss-cert-v01@openssh.com,ssh-dss-cert-v00@openssh.com,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-sha2-256-96,hmac-sha2-512,hmac-sha2-512-96,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-sha2-256-96,hmac-sha2-512,hmac-sha2-512-96,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: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,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,ecdsa-sha2-nistp256
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
debug2: dh_gen_key: priv key bits set: 130/256
debug2: bits set: 503/1024
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Server host key: RSA dc:21:77:3b:f4:4e:74:d0:87:33:14:40:04:68:33:a6
debug3: load_hostkeys: loading entries for host "x.acme.com" from file "/Users/tfergeson/.ssh/known_hosts"
debug3: load_hostkeys: found key type RSA in file /Users/tfergeson/.ssh/known_hosts:10
debug3: load_hostkeys: loaded 1 keys
debug3: load_hostkeys: loading entries for host "69.137.56.18" from file "/Users/tfergeson/.ssh/known_hosts"
debug3: load_hostkeys: found key type RSA in file /Users/tfergeson/.ssh/known_hosts:6
debug3: load_hostkeys: loaded 1 keys
debug1: Host 'x.acme.com' is known and matches the RSA host key.
debug1: Found key in /Users/tfergeson/.ssh/known_hosts:10
debug2: bits set: 493/1024
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: /Users/tfergeson/.ssh/id_rsa (0x7ff189c1d7d0)
debug2: key: /Users/tfergeson/.ssh/id_dsa (0x0)
debug1: Authentications that can continue: publickey
debug3: start over, passed a different list publickey
debug3: preferred publickey,keyboard-interactive,password
debug3: authmethod_lookup publickey
debug3: remaining preferred: keyboard-interactive,password
debug3: authmethod_is_enabled publickey
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /Users/tfergeson/.ssh/id_rsa
debug3: send_pubkey_test
debug2: we sent a publickey packet, wait for reply
debug1: Server accepts key: pkalg ssh-rsa blen 277
debug2: input_userauth_pk_ok: fp 3c:e5:29:6c:9d:27:d1:7d:e8:09:a2:e8:8e:6e:af:6f
debug3: sign_and_send_pubkey: RSA 3c:e5:29:6c:9d:27:d1:7d:e8:09:a2:e8:8e:6e:af:6f
debug1: read PEM private key done: type RSA
debug1: Authentication succeeded (publickey).
Authenticated to x.acme.com ([69.137.56.18]:22).
debug1: channel 0: new [client-session]
debug3: ssh_session2_open: channel_new: 0
debug2: channel 0: send open
debug1: Requesting no-more-sessions@openssh.com
debug1: Entering interactive session.
debug2: callback start
debug2: client_session2_setup: id 0
debug2: fd 3 setting TCP_NODELAY
debug2: channel 0: request pty-req confirm 1
debug1: Sending environment.
debug3: Ignored env ATLAS_OPTS
debug3: Ignored env rvm_bin_path
debug3: Ignored env TERM_PROGRAM
debug3: Ignored env GEM_HOME
debug3: Ignored env SHELL
debug3: Ignored env TERM
debug3: Ignored env CLICOLOR
debug3: Ignored env IRBRC
debug3: Ignored env TMPDIR
debug3: Ignored env Apple_PubSub_Socket_Render
debug3: Ignored env TERM_PROGRAM_VERSION
debug3: Ignored env MY_RUBY_HOME
debug3: Ignored env TERM_SESSION_ID
debug3: Ignored env USER
debug3: Ignored env COMMAND_MODE
debug3: Ignored env rvm_path
debug3: Ignored env COM_GOOGLE_CHROME_FRAMEWORK_SERVICE_PROCESS/USERS/tfergeson/LIBRARY/APPLICATION_SUPPORT/GOOGLE/CHROME_SOCKET
debug3: Ignored env JPDA_ADDRESS
debug3: Ignored env APDK_HOME
debug3: Ignored env SSH_AUTH_SOCK
debug3: Ignored env Apple_Ubiquity_Message
debug3: Ignored env __CF_USER_TEXT_ENCODING
debug3: Ignored env rvm_sticky_flag
debug3: Ignored env MAVEN_OPTS
debug3: Ignored env LSCOLORS
debug3: Ignored env rvm_prefix
debug3: Ignored env PATH
debug3: Ignored env PWD
debug3: Ignored env JAVA_HOME
debug1: Sending env LANG = en_US.UTF-8
debug2: channel 0: request env confirm 0
debug3: Ignored env JPDA_TRANSPORT
debug3: Ignored env rvm_version
debug3: Ignored env M2_HOME
debug3: Ignored env HOME
debug3: Ignored env SHLVL
debug3: Ignored env rvm_ruby_string
debug3: Ignored env LOGNAME
debug3: Ignored env M2_REPO
debug3: Ignored env GEM_PATH
debug3: Ignored env AWS_RDS_HOME
debug3: Ignored env rvm_delete_flag
debug3: Ignored env EC2_PRIVATE_KEY
debug3: Ignored env RUBY_VERSION
debug3: Ignored env SECURITYSESSIONID
debug3: Ignored env EC2_CERT
debug3: Ignored env _
debug2: channel 0: request shell confirm 1
debug2: callback done
debug2: channel 0: open confirm rwindow 0 rmax 32768

我可以硬重启（只有那个位置的 mac 显示器），它可以再次访问。现在每次都会发生这种情况。我必须把它整理好。奇怪的是，它最初的行为然后在几个小时后开始挂起。我以前仔细阅读过日志，没有什么特别突出的。

从 auth.log 中，我可以看到它允许我进入，但在客户端我仍然没有得到任何回报：

Sep 20 12:47:50 cbear sshd[25376]: Accepted publickey for tfergeson from 10.1.10.14 port 54631 ssh2
Sep 20 12:47:50 cbear sshd[25376]: pam_unix(sshd:session): session opened for user tfergeson by (uid=0)

更新：

即使设置UseDNS no和注释掉后仍然发生#session optional pam_mail.so standard noenv

这似乎不是与网络/dns 相关的问题，因为机器上运行的所有服务都像以往一样响应和可访问，除了sshd.

关于从哪里开始的任何想法？

Answer 1

从GNU Savannah 文档 wiki 上的SshAccess 页面：

当您尝试使用 OpenSSH 从 NAT 路由器后面进行连接时，可能会出现问题。在会话设置期间，在给出密码后，OpenSSH 设置 IP 数据报中的 TOS（服务类型）字段。众所周知，某些路由器会因此而窒息。结果是您的会话在您提供密码后无限期挂起。以下是此类 ssh 会话的示例输出：

user@localhost:~$ ssh -vvv {user-name}@cvs.savannah.gnu.org
OpenSSH_4.7p1 Debian-8ubuntu1.2, OpenSSL 0.9.8g 19 Oct 2007
debug1: Reading configuration data /etc/ssh/ssh_config
[...]
Enter passphrase for key '{homedir}/.ssh/id_rsa':
debug1: read PEM private key done: type RSA
debug1: Authentication succeeded (publickey).
[...]
debug2: fd 5 setting TCP_NODELAY
debug2: callback done
debug2: channel 0: open confirm rwindow 0 rmax 32768

从这里开始会话挂起。

解决方法是让 ssh 通过 netcat 发送其所有流量，因为 netcat 不会设置 TOS 字段。为此，您需要安装 netcat。您可以通过在命令行中输入来测试：

user@localhost:~$ which nc

如果你有一条路回来，比如：

/bin/nc

那么你可能已经安装了netcat。对于非常谨慎的人，您还可以发出：

user@localhost:~$ nc -h

并查看即将发布的帮助文本。如果你没有 netcat，你可以在http://netcat.sourceforge.net/找到它。您可能还想尝试操作系统发行版附带的打包系统。

一旦你发现你已经安装了 netcat，发出以下命令来测试 netcat 路由是否解决了你的问题：

ssh -o "ProxyCommand nc %h %p" {user-name}@cvs.savannah.gnu.org

其中 {user-name} 是您的 savannah 登录名。对于成功登录，您应该得到与此类似的输出（没有挂起，即之后您会收到提示）：

user@localhost:~$ ssh -o "ProxyCommand nc %h %p" {user-name}@cvs.savannah.gnu.org
Enter passphrase for key '{home-dir}/.ssh/id_rsa': 
Last login: {datetime} from {ip-adr} 
You tried to execute: 
Sorry, you are not allowed to execute that command. 
Connection to cvs.savannah.gnu.org closed. 
user@localhost:~$

如果你发现你的登录是通过 netcat 路由工作的，那么你可以通过向 ssh 配置文件添加一个指令来使其永久化 ~/.ssh/config（或者，如果该文件不存在，则创建它）：

ProxyCommand nc %h %p

以下是用户主文件夹 (/home/user/.ssh/config) 中的示例 ssh 配置文件：

# This is the ssh client user configuration file.  See
# ssh_config(5) for more information.  This file provides defaults for
# this user, and the values can be changed on the command line.
#
# Configuration data is parsed as follows:
#  1. command line options
#  2. user-specific file
#  3. system-wide file
# Any configuration value is only changed the first time it is set.
# Thus, host-specific definitions should be at the beginning of the
# configuration file, and defaults at the end.
#
# Directive to overcome TOS issue with our NAT router. During session setup,
# OpenSSH sets the TOS (type of service) field after the user has submitted
# the password. Some routers are known to choke on this, with the result
# that the session hangs during buildup. As workaround we send our traffic
# via netcat which doesn't set the TOS field.
ProxyCommand nc %h %p

建议也发表评论，否则六个月后您可能会发现自己想知道该指令是关于什么的？

您也可以将此指令添加到您的全局 ssh 配置文件 ( /etc/ssh/ssh_config)，但此更改将是系统范围的，并且并非您系统上的所有用户都可能会欣赏该更改。

Answer 2

ssh -o IPQoS=0 x.acme.com 应该告诉 openssh 停止设置被阻塞的 QoS 字段。

Answer 3

尽管这听起来很荒谬，但我目前唯一的解决方法是安排每晚重新启动。幸运的是，这种解决方法是可以接受的，因为它是一台开发机器，如果它是一台生产机器，我就会遇到麻烦。

我讨厌这个，但想确保其他找到这个帖子的人知道我没有解决方案。将其添加到根 crontab 以便每晚凌晨 4 点重新启动：

0 4 * * * /sbin/shutdown -r +5