Recently we upgraded the server from 12.04 LTS server to 13.04. All was well, including after a reboot. With all packages updated we began to see a strange issue, ssh works for a day or so (unclear on timing) then a later request for SSH hangs (cannot ctrl+c, nothing).

It is up and serving webserver traffic etc.

Port 22 is open (ips etc altered slightly for posting):

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

Here is the 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: [email protected],[email protected],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: [email protected],[email protected],ssh-rsa,[email protected],[email protected],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,[email protected]
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,[email protected]
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-sha2-256,hmac-sha2-256-96,hmac-sha2-512,hmac-sha2-512-96,hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-sha2-256,hmac-sha2-256-96,hmac-sha2-512,hmac-sha2-512-96,hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: none,[email protected],zlib
debug2: kex_parse_kexinit: none,[email protected],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,[email protected]
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,[email protected]
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: none,[email protected]
debug2: kex_parse_kexinit: none,[email protected]
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 [email protected]
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

I can hard reboot (only mac monitors at that location) and it will again be accessible. This now happens every single time. It is imperative that I get it sorted. The strange thing is that it behaves initially then starts to hang after several hours. I perused logs previously and nothing stood out.

From the auth.log, I can see that it has allowed me in, but still I get nothing back on the client side:

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)

UPDATES:

Still occurring even after setting UseDNS no and commenting out #session optional pam_mail.so standard noenv

This does not appear to be a network/dns related issue, as all services running on the machine are as responsive and accessible as ever, with the exception of sshd.

Any thoughts on where to start?