ssh hangs after successfull login

From: Zhang Weiwu (zhangweiwu_at_realss.com)
Date: 10/26/05 

Date: Wed, 26 Oct 2005 08:46:36 +0800

Hello. I am not sure if my problem is exactly the one mensioned in this
document but it isn't really alike
http://www.snailbook.com/faq/mtu-mismatch.auto.html

Yesterday everything was fine with my host in uk (that is half an earth
from my desktop) untill today morning I found I no longer able to login
to the host by ssh. The behavior is that after successfully
authenticated, ssh hangs up forever.

A quick google brought me to the above article saying that perhaps my
MTU has problematic settings. I got no chance to adjust MTU of the
remote uk server (becuase ssh is the only way I can get to the server,
besides a phone call to cold-boot it) to test. But I also tried to login
from 3 different linux hosts and two of them do not have NAT nor
firewall nor packet filter.

Here is the log for your reference. All 3 hosts runs Gentoo Linux

Thank you!

from host 'bossdog' (no firewall/NAT/packet filter)
> zhangweiwu@bossdog zhangweiwu $ ssh -vvv realss.vm.bytemark.co.uk
> OpenSSH_3.9p1, OpenSSL 0.9.7e 25 Oct 2004
> debug1: Reading configuration data /etc/ssh/ssh_config
> debug2: ssh_connect: needpriv 0
> debug1: Connecting to realss.vm.bytemark.co.uk [80.68.93.152] port 22.
> debug1: Connection established.
> debug1: identity file /home/zhangweiwu/.ssh/identity type -1
> debug1: identity file /home/zhangweiwu/.ssh/id_rsa type -1
> debug1: identity file /home/zhangweiwu/.ssh/id_dsa type -1
> debug1: Remote protocol version 2.0, remote software version OpenSSH_3.9p1
> debug1: match: OpenSSH_3.9p1 pat OpenSSH*
> debug1: Enabling compatibility mode for protocol 2.0
> debug1: Local version string SSH-2.0-OpenSSH_3.9p1
> debug2: fd 3 setting O_NONBLOCK
> debug1: SSH2_MSG_KEXINIT sent
> debug1: SSH2_MSG_KEXINIT received
> 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,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,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
> debug2: kex_parse_kexinit: none,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,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,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
> debug2: kex_parse_kexinit: none,zlib
> debug2: kex_parse_kexinit:
> debug2: kex_parse_kexinit:
> debug2: kex_parse_kexinit: first_kex_follows 0
> debug2: kex_parse_kexinit: reserved 0
> debug2: mac_init: found hmac-md5
> debug1: kex: server->client aes128-cbc hmac-md5 none
> debug2: mac_init: found hmac-md5
> debug1: kex: client->server aes128-cbc 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: 127/256
> debug2: bits set: 515/1024
> debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
> debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
> debug3: check_host_in_hostfile: filename /home/zhangweiwu/.ssh/known_hosts
> debug3: check_host_in_hostfile: filename /etc/ssh/ssh_known_hosts
> debug3: check_host_in_hostfile: filename /home/zhangweiwu/.ssh/known_hosts
> debug3: check_host_in_hostfile: filename /etc/ssh/ssh_known_hosts
> debug3: check_host_in_hostfile: filename /home/zhangweiwu/.ssh/known_hosts
> debug3: check_host_in_hostfile: filename /etc/ssh/ssh_known_hosts
> debug2: no key of type 0 for host realss.vm.bytemark.co.uk
> debug3: check_host_in_hostfile: filename /home/zhangweiwu/.ssh/known_hosts2
> debug3: check_host_in_hostfile: filename /etc/ssh/ssh_known_hosts2
> debug3: check_host_in_hostfile: filename /home/zhangweiwu/.ssh/known_hosts
> debug3: check_host_in_hostfile: filename /etc/ssh/ssh_known_hosts
> debug2: no key of type 2 for host realss.vm.bytemark.co.uk
> The authenticity of host 'realss.vm.bytemark.co.uk (80.68.93.152)' can't be established.
> RSA key fingerprint is 6c:af:37:c2:89:93:3a:3d:c4:f5:ce:27:44:57:16:48.
> Are you sure you want to continue connecting (yes/no)? yes
> Failed to add the host to the list of known hosts (/home/zhangweiwu/.ssh/known_hosts).
> debug2: bits set: 513/1024
> 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: SSH2_MSG_SERVICE_REQUEST sent
> debug2: service_accept: ssh-userauth
> debug1: SSH2_MSG_SERVICE_ACCEPT received
> debug2: key: /home/zhangweiwu/.ssh/identity ((nil))
> debug2: key: /home/zhangweiwu/.ssh/id_rsa ((nil))
> debug2: key: /home/zhangweiwu/.ssh/id_dsa ((nil))
> debug1: Authentications that can continue: publickey,keyboard-interactive
> debug3: start over, passed a different list publickey,keyboard-interactive
> 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: Trying private key: /home/zhangweiwu/.ssh/identity
> debug3: no such identity: /home/zhangweiwu/.ssh/identity
> debug1: Trying private key: /home/zhangweiwu/.ssh/id_rsa
> debug3: no such identity: /home/zhangweiwu/.ssh/id_rsa
> debug1: Trying private key: /home/zhangweiwu/.ssh/id_dsa
> debug3: no such identity: /home/zhangweiwu/.ssh/id_dsa
> debug2: we did not send a packet, disable method
> debug3: authmethod_lookup keyboard-interactive
> debug3: remaining preferred: password
> debug3: authmethod_is_enabled keyboard-interactive
> debug1: Next authentication method: keyboard-interactive
> debug2: userauth_kbdint
> debug2: we sent a keyboard-interactive packet, wait for reply
> debug2: input_userauth_info_req
> debug2: input_userauth_info_req: num_prompts 1
> Password:
> debug3: packet_send2: adding 32 (len 22 padlen 10 extra_pad 64)
> debug2: input_userauth_info_req
> debug2: input_userauth_info_req: num_prompts 0
> debug3: packet_send2: adding 48 (len 10 padlen 6 extra_pad 64)
> debug1: Authentication succeeded (keyboard-interactive).
> debug1: channel 0: new [client-session]
> debug3: ssh_session2_open: channel_new: 0
> debug2: channel 0: send open
> debug1: Entering interactive session.
(then hangs on forever)

from host Joe (behind NAT)
> zhangweiwu@Joe ~ $ ssh -vvv root@www.xn--vusz75b9ihq1cr41e.net
> OpenSSH_3.9p1, OpenSSL 0.9.7e 25 Oct 2004
> debug1: Reading configuration data /etc/ssh/ssh_config
> debug2: ssh_connect: needpriv 0
> debug1: Connecting to www.xn--vusz75b9ihq1cr41e.net [80.68.93.152] port 22.
> debug1: Connection established.
> debug1: identity file /home/zhangweiwu/.ssh/identity type -1
> debug1: identity file /home/zhangweiwu/.ssh/id_rsa type -1
> debug3: Not a RSA1 key file /home/zhangweiwu/.ssh/id_dsa.
> debug2: key_type_from_name: unknown key type '-----BEGIN'
> debug3: key_read: missing keytype
> debug3: key_read: missing whitespace
> debug3: key_read: missing whitespace
> debug3: key_read: missing whitespace
> debug3: key_read: missing whitespace
> debug3: key_read: missing whitespace
> debug3: key_read: missing whitespace
> debug3: key_read: missing whitespace
> debug3: key_read: missing whitespace
> debug3: key_read: missing whitespace
> debug3: key_read: missing whitespace
> debug2: key_type_from_name: unknown key type '-----END'
> debug3: key_read: missing keytype
> debug1: identity file /home/zhangweiwu/.ssh/id_dsa type 2
> debug1: Remote protocol version 2.0, remote software version OpenSSH_3.9p1
> debug1: match: OpenSSH_3.9p1 pat OpenSSH*
> debug1: Enabling compatibility mode for protocol 2.0
> debug1: Local version string SSH-2.0-OpenSSH_3.9p1
> debug2: fd 3 setting O_NONBLOCK
> debug1: SSH2_MSG_KEXINIT sent
> debug1: SSH2_MSG_KEXINIT received
> 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,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,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
> debug2: kex_parse_kexinit: none,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,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,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
> debug2: kex_parse_kexinit: none,zlib
> debug2: kex_parse_kexinit:
> debug2: kex_parse_kexinit:
> debug2: kex_parse_kexinit: first_kex_follows 0
> debug2: kex_parse_kexinit: reserved 0
> debug2: mac_init: found hmac-md5
> debug1: kex: server->client aes128-cbc hmac-md5 none
> debug2: mac_init: found hmac-md5
> debug1: kex: client->server aes128-cbc 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: 113/256
> debug2: bits set: 515/1024
> debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
> debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
> debug3: check_host_in_hostfile: filename /home/zhangweiwu/.ssh/known_hosts
> debug3: check_host_in_hostfile: match line 24
> debug3: check_host_in_hostfile: filename /home/zhangweiwu/.ssh/known_hosts
> debug3: check_host_in_hostfile: match line 23
> debug1: Host 'www.xn--vusz75b9ihq1cr41e.net' is known and matches the RSA host key.
> debug1: Found key in /home/zhangweiwu/.ssh/known_hosts:24
> debug2: bits set: 512/1024
> 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: SSH2_MSG_SERVICE_REQUEST sent
> debug2: service_accept: ssh-userauth
> debug1: SSH2_MSG_SERVICE_ACCEPT received
> debug2: key: /home/zhangweiwu/.ssh/identity ((nil))
> debug2: key: /home/zhangweiwu/.ssh/id_rsa ((nil))
> debug2: key: /home/zhangweiwu/.ssh/id_dsa (0x8094f60)
> debug1: Authentications that can continue: publickey,keyboard-interactive
> debug3: start over, passed a different list publickey,keyboard-interactive
> 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: Trying private key: /home/zhangweiwu/.ssh/identity
> debug3: no such identity: /home/zhangweiwu/.ssh/identity
> debug1: Trying private key: /home/zhangweiwu/.ssh/id_rsa
> debug3: no such identity: /home/zhangweiwu/.ssh/id_rsa
> debug1: Offering public key: /home/zhangweiwu/.ssh/id_dsa
> debug3: send_pubkey_test
> debug2: we sent a publickey packet, wait for reply
> debug1: Server accepts key: pkalg ssh-dss blen 434
> debug2: input_userauth_pk_ok: fp c0:3c:84:e1:f0:ae:bf:7d:12:4b:70:a1:44:be:db:46debug3: sign_and_send_pubkey
> debug1: read PEM private key done: type DSA
> debug1: Authentication succeeded (publickey).
> debug1: channel 0: new [client-session]
> debug3: ssh_session2_open: channel_new: 0
> debug2: channel 0: send open
> debug1: Entering interactive session.
> debug2: callback start
> debug1: Requesting authentication agent forwarding.
> debug2: channel 0: request auth-agent-req@openssh.com confirm 0
> debug2: client_session2_setup: id 0
> debug2: channel 0: request pty-req confirm 0
> debug3: tty_make_modes: ospeed 38400
> debug3: tty_make_modes: ispeed 38400
> debug3: tty_make_modes: 1 3
> debug3: tty_make_modes: 2 28
> debug3: tty_make_modes: 3 127
> debug3: tty_make_modes: 4 21
> debug3: tty_make_modes: 5 4
> debug3: tty_make_modes: 6 255
> debug3: tty_make_modes: 7 255
> debug3: tty_make_modes: 8 17
> debug3: tty_make_modes: 9 19
> debug3: tty_make_modes: 10 26
> debug3: tty_make_modes: 12 18
> debug3: tty_make_modes: 13 23
> debug3: tty_make_modes: 14 22
> debug3: tty_make_modes: 18 15
> debug3: tty_make_modes: 30 0
> debug3: tty_make_modes: 31 0
> debug3: tty_make_modes: 32 0
> debug3: tty_make_modes: 33 0
> debug3: tty_make_modes: 34 0
> debug3: tty_make_modes: 35 0
> debug3: tty_make_modes: 36 1
> debug3: tty_make_modes: 37 0
> debug3: tty_make_modes: 38 1
> debug3: tty_make_modes: 39 1
> debug3: tty_make_modes: 40 0
> debug3: tty_make_modes: 41 1
> debug3: tty_make_modes: 50 1
> debug3: tty_make_modes: 51 1
> debug3: tty_make_modes: 52 0
> debug3: tty_make_modes: 53 1
> debug3: tty_make_modes: 54 1
> debug3: tty_make_modes: 55 1
> debug3: tty_make_modes: 56 0
> debug3: tty_make_modes: 57 0
> debug3: tty_make_modes: 58 0
> debug3: tty_make_modes: 59 1
> debug3: tty_make_modes: 60 1
> debug3: tty_make_modes: 61 1
> debug3: tty_make_modes: 62 0
> debug3: tty_make_modes: 70 1
> debug3: tty_make_modes: 71 0
> debug3: tty_make_modes: 72 1
> debug3: tty_make_modes: 73 0
> debug3: tty_make_modes: 74 0
> debug3: tty_make_modes: 75 0
> debug3: tty_make_modes: 90 1
> debug3: tty_make_modes: 91 1
> debug3: tty_make_modes: 92 0
> debug3: tty_make_modes: 93 0
> debug2: channel 0: request shell confirm 0
> debug2: fd 3 setting TCP_NODELAY
> debug2: callback done
> debug2: channel 0: open confirm rwindow 0 rmax 32768
> debug2: channel 0: rcvd adjust 131072
(then hangs on forever)

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