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My brand new centos server has some trouble with openssh. The shell freezes, sometimes after 10 seconds, sometimes after 2-3 minutes. (Connection closed by host) When the shell freezes, I can't log in again for about 10 minutes.

I tried all the classic solutions like enabling the KeepAlive interval, disabling DNS, and disabling the GSSAPIAuthentication.

SELinux and iptables are disabled.

Last lines of my /var/log/secure:

Nov 17 04:33:07 tp sshd[2152]: Received disconnect from 194.190.136.163: 11: Bye Bye
Nov 17 04:33:07 tp sshd[2153]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=194.190.136.163  user=root
Nov 17 04:33:09 tp sshd[2153]: Failed password for root from 194.190.136.163 port 48488 ssh2
Nov 17 04:33:09 tp sshd[2154]: Received disconnect from 194.190.136.163: 11: Bye Bye
Nov 17 04:33:10 tp sshd[2155]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=194.190.136.163  user=root
Nov 17 04:33:12 tp sshd[2155]: Failed password for root from 194.190.136.163 port 48737 ssh2
Nov 17 10:35:37 tp sshd[2299]: Accepted password for root from 37.221.161.234 port 47783 ssh2
Nov 17 10:35:37 tp sshd[2299]: pam_unix(sshd:session): session opened for user root by (uid=0)

The debug after ssh -vvv:

OpenSSH_6.1p1, OpenSSL 1.0.0-fips 29 Mar 2010
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 51: Applying options for *
debug2: ssh_connect: needpriv 0
debug1: Connecting to ipserver [ipserver] port 22.
debug1: Connection established.
debug1: identity file /home/masufasu/.ssh/id_rsa type -1
debug1: identity file /home/masufasu/.ssh/id_rsa-cert type -1
debug1: identity file /home/masufasu/.ssh/id_dsa type -1
debug1: identity file /home/masufasu/.ssh/id_dsa-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.3
debug1: match: OpenSSH_5.3 pat OpenSSH_5*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.1
debug2: fd 3 setting O_NONBLOCK
debug3: load_hostkeys: loading entries for host "ipserver" from file "/home/masufasu/.ssh/known_hosts"
debug3: load_hostkeys: found key type RSA in file /home/masufasu/.ssh/known_hosts:5
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-sha2-512,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,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-sha256,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-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
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: 128/256
debug2: bits set: 473/1024
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Server host key: RSA cf:f9:ec:46:7d:61:78:ec:ff:b3:c4:a6:1f:42:f0:ea
debug3: load_hostkeys: loading entries for host "ipserver" from file "/home/masufasu/.ssh/known_hosts"
debug3: load_hostkeys: found key type RSA in file /home/masufasu/.ssh/known_hosts:5
debug3: load_hostkeys: loaded 1 keys
debug1: Host 'ipserver' is known and matches the RSA host key.
debug1: Found key in /home/masufasu/.ssh/known_hosts:5
debug2: bits set: 495/1024
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/masufasu/.ssh/id_rsa ((nil))
debug2: key: /home/masufasu/.ssh/id_dsa ((nil))
debug1: Authentications that can continue: publickey,password
debug3: start over, passed a different list publickey,password
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/masufasu/.ssh/id_rsa
debug3: no such identity: /home/masufasu/.ssh/id_rsa
debug1: Trying private key: /home/masufasu/.ssh/id_dsa
debug3: no such identity: /home/masufasu/.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
debug3: packet_send2: adding 64 (len 60 padlen 4 extra_pad 64)
debug2: we sent a password packet, wait for reply
debug1: Authentication succeeded (password).
Authenticated to ipserver ([ipserver]:22).
debug2: fd 5 setting O_NONBLOCK
debug3: fd 6 is O_NONBLOCK
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: fd 3 setting TCP_NODELAY
debug3: packet_set_tos: set IP_TOS 0x10
debug2: client_session2_setup: id 0
debug2: channel 0: request pty-req confirm 1
debug1: Sending environment.
debug3: Ignored env XDG_VTNR
debug3: Ignored env XDG_SESSION_ID
debug3: Ignored env HOSTNAME
debug3: Ignored env IMSETTINGS_INTEGRATE_DESKTOP
debug3: Ignored env GPG_AGENT_INFO
debug3: Ignored env TERM
debug3: Ignored env SHELL
debug3: Ignored env XDG_MENU_PREFIX
debug3: Ignored env HISTSIZE
debug3: Ignored env XDG_SESSION_COOKIE
debug3: Ignored env GJS_DEBUG_OUTPUT
debug3: Ignored env WINDOWID
debug3: Ignored env GNOME_KEYRING_CONTROL
debug3: Ignored env QTDIR
debug3: Ignored env QTINC
debug3: Ignored env GJS_DEBUG_TOPICS
debug3: Ignored env IMSETTINGS_MODULE
debug3: Ignored env QT_GRAPHICSSYSTEM_CHECKED
debug3: Ignored env USER
debug3: Ignored env LS_COLORS
debug3: Ignored env SSH_AUTH_SOCK
debug3: Ignored env SESSION_MANAGER
debug3: Ignored env USERNAME
debug3: Ignored env PATH
debug3: Ignored env MAIL
debug3: Ignored env DESKTOP_SESSION
debug3: Ignored env QT_IM_MODULE
debug3: Ignored env PWD
debug1: Sending env XMODIFIERS = @im=ibus
debug2: channel 0: request env confirm 0
debug3: Ignored env GNOME_KEYRING_PID
debug1: Sending env LANG = it_IT.UTF-8
debug2: channel 0: request env confirm 0
debug3: Ignored env KDE_IS_PRELINKED
debug3: Ignored env KDEDIRS
debug3: Ignored env AUTOJUMP_DATA_DIR
debug3: Ignored env GDMSESSION
debug3: Ignored env HISTCONTROL
debug3: Ignored env KRB5CCNAME
debug3: Ignored env XDG_SEAT
debug3: Ignored env HOME
debug3: Ignored env SHLVL
debug3: Ignored env GNOME_DESKTOP_SESSION_ID
debug3: Ignored env AUTOJUMP_HOME
debug3: Ignored env LOGNAME
debug3: Ignored env QTLIB
debug3: Ignored env DBUS_SESSION_BUS_ADDRESS
debug3: Ignored env LESSOPEN
debug3: Ignored env PROMPT_COMMAND
debug3: Ignored env WINDOWPATH
debug3: Ignored env XDG_RUNTIME_DIR
debug3: Ignored env DISPLAY
debug3: Ignored env QT_PLUGIN_PATH
debug3: Ignored env COLORTERM
debug3: Ignored env XAUTHORITY
debug3: Ignored env _
debug2: channel 0: request shell confirm 1
debug2: callback done
debug2: channel 0: open confirm rwindow 0 rmax 32768
debug2: channel_input_status_confirm: type 99 id 0
debug2: PTY allocation request accepted on channel 0
debug2: channel 0: rcvd adjust 2097152
debug2: channel_input_status_confirm: type 99 id 0
debug2: shell request accepted on channel 0
Last login: Sat Nov 16 18:38:52 2013 from 2.237.239.68

]0;root@tp:~[?1034h[root@tp ~]# debug1: client_input_channel_req: channel 0 rtype keepalive@openssh.com reply 1
debug1: client_input_channel_req: channel 0 rtype keepalive@openssh.com reply 1
debug1: client_input_channel_req: channel 0 rtype keepalive@openssh.com reply 1
debug1: client_input_channel_req: channel 0 rtype keepalive@openssh.com reply 1
debug1: client_input_channel_req: channel 0 rtype keepalive@openssh.com reply 1
debug1: client_input_channel_req: channel 0 rtype keepalive@openssh.com reply 1
debug1: client_input_channel_req: channel 0 rtype keepalive@openssh.com reply 1
debug1: client_input_channel_req: channel 0 rtype keepalive@openssh.com reply 1
debug1: client_input_channel_req: channel 0 rtype keepalive@openssh.com reply 1
debug1: client_input_channel_req: channel 0 rtype keepalive@openssh.com reply 1
debug1: client_input_channel_req: channel 0 rtype keepalive@openssh.com reply 1
debug1: client_input_channel_req: channel 0 rtype keepalive@openssh.com reply 1
debug1: client_input_channel_req: channel 0 rtype keepalive@openssh.com reply 1
debug1: client_input_channel_req: channel 0 rtype keepalive@openssh.com reply 1
debug1: client_input_channel_req: channel 0 rtype keepalive@openssh.com reply 1
debug1: client_input_channel_req: channel 0 rtype keepalive@openssh.com reply 1
debug1: client_input_channel_req: channel 0 rtype keepalive@openssh.com reply 1
debug1: client_input_channel_req: channel 0 rtype keepalive@openssh.com reply 1
debug1: client_input_channel_req: channel 0 rtype keepalive@openssh.com reply 1
debug1: client_input_channel_req: channel 0 rtype keepalive@openssh.com reply 1
debug1: channel 0: free: client-session, nchannels 1
debug3: channel 0: status: The following connections are open:
  #0 client-session (t4 r0 i0/0 o0/0 fd 4/5 cc -1)

debug1: fd 1 clearing O_NONBLOCK
debug3: fd 2 is not O_NONBLOCK
Connection to ipserver closed by remote host.
Connection to ipserver closed.
Transferred: sent 2312, received 2952 bytes, in 211.2 seconds
Bytes per second: sent 10.9, received 14.0
debug1: Exit status -1

netstat -lnpt | grep 22:

tcp        0      0 0.0.0.0:22                  0.0.0.0:*                   LISTEN      1495/sshd           
tcp        0      0 :::22                       :::*                        LISTEN      1495/sshd   

/var/log/messages

nf_conntrack version 0.5.0 (16384 buckets, 65536 max)
r8169 0000:02:00.0: firmware: requesting rtl_nic/rtl8168e-3.fw
r8169 0000:02:00.0: eth0: link down
r8169 0000:02:00.0: eth0: link down
ADDRCONF(NETDEV_UP): eth0: link is not ready
r8169 0000:02:00.0: eth0: link up
ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
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1 Answer 1

Are you able to scp a largeish file to and from the server?

If not and it starts to fail almost immediately, you have a path MTU issue between the client and server.

If so, you likely have an overly aggressive firewall somewhere timing out states, or without any room in its state table. Do you have bittorrent users on the network? That protocol can be very hard on state tables.

share|improve this answer
    
I moved 1tb of files with rsync, it crashed every hour or so. But now scp works without problems: scp dumpdef.sql root@185.xx.xx.xx:~/dumpdef.sql root@185.xx.xx.xx's password: dumpdef.sql 100% 415MB 10.1MB/s 00:41 –  lexolas Nov 17 '13 at 14:08

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