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I use ubuntu 14.04 and I connect through SSH to a dozen odd servers both physical machines and virtual ones on the cloud.

On one of my servers I used to connect through an RSA Authentication Key, I could connect to the server both as a user as well as root. But within few seconds, the ssh session hangs.

This behavior is observed only from my machine. I tested connecting to the same server from windows (through putty) as well as a linux server through xterm. Both were successful and was working normally.

From my machine where I have this problem, I am still able to connect with the rest of the other servers, without any trouble.

I couldn't figure out what could be the possible issue with this particular server?

The server uses RHEL 6.8.

The following is the verbose error output:

debug1: Reading configuration data /etc/ssh/ssh_config debug1: /etc/ssh/ssh_config line 19: Applying options for * debug2: ssh_connect: needpriv 0 debug1: Connecting to 192.168.1.192 [192.168.1.192] port 22. debug1: Connection established. debug3: Incorrect RSA1 identifier debug3: Could not load "/home/ir_comp_N232/.ssh/id_rsa" as a RSA1 public key debug1: identity file /home/ir_comp_N232/.ssh/id_rsa type 1 debug1: identity file /home/ir_comp_N232/.ssh/id_rsa-cert type -1 debug1: identity file /home/ir_comp_N232/.ssh/id_dsa type -1 debug1: identity file /home/ir_comp_N232/.ssh/id_dsa-cert type -1 debug1: identity file /home/ir_comp_N232/.ssh/id_ecdsa type -1 debug1: identity file /home/ir_comp_N232/.ssh/id_ecdsa-cert type -1 debug1: identity file /home/ir_comp_N232/.ssh/id_ed25519 type -1 debug1: identity file /home/ir_comp_N232/.ssh/id_ed25519-cert type -1 debug1: Enabling compatibility mode for protocol 2.0 debug1: Local version string SSH-2.0-OpenSSH_6.6.1p1 Ubuntu-2ubuntu2.10 debug1: Remote protocol version 2.0, remote software version OpenSSH_5.3 debug1: match: OpenSSH_5.3 pat OpenSSH_5* compat 0x0c000000 debug2: fd 3 setting O_NONBLOCK debug3: load_hostkeys: loading entries for host "192.168.1.192" from file "/home/ir_comp_N232/.ssh/known_hosts" debug3: load_hostkeys: found key type RSA in file /home/ir_comp_N232/.ssh/known_hosts:3 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: [email protected],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: [email protected],[email protected],ssh-rsa,[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-ed25519,ssh-dss debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,[email protected],[email protected],[email protected],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,[email protected],[email protected],[email protected],aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,[email protected] debug2: kex_parse_kexinit: [email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],hmac-md5,hmac-sha1,[email protected],[email protected],hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96 debug2: kex_parse_kexinit: [email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],hmac-md5,hmac-sha1,[email protected],[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],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: 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,[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: setup hmac-md5 debug1: kex: server->client aes128-ctr hmac-md5 none debug2: mac_setup: setup hmac-md5 debug1: kex: client->server aes128-ctr hmac-md5 none debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<3072<8192) sent debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP debug2: bits set: 1541/3072 debug1: SSH2_MSG_KEX_DH_GEX_INIT sent debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY debug1: Server host key: RSA 44:95:bf:bf:90:04:aa:72:80:77:17:29:84:42:3e:48 debug3: load_hostkeys: loading entries for host "192.168.1.192" from file "/home/ir_comp_N232/.ssh/known_hosts" debug3: load_hostkeys: found key type RSA in file /home/ir_comp_N232/.ssh/known_hosts:3 debug3: load_hostkeys: loaded 1 keys debug1: Host '192.168.1.192' is known and matches the RSA host key. debug1: Found key in /home/ir_comp_N232/.ssh/known_hosts:3 debug2: bits set: 1531/3072 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/ir_comp_N232/.ssh/id_rsa (0x55627af25490), debug2: key: /home/ir_comp_N232/.ssh/id_dsa ((nil)), debug2: key: /home/ir_comp_N232/.ssh/id_ecdsa ((nil)), debug2: key: /home/ir_comp_N232/.ssh/id_ed25519 ((nil)), debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password debug3: start over, passed a different list publickey,gssapi-keyex,gssapi-with-mic,password debug3: preferred gssapi-keyex,gssapi-with-mic,publickey,keyboard-interactive,password debug3: authmethod_lookup gssapi-keyex debug3: remaining preferred: gssapi-with-mic,publickey,keyboard-interactive,password debug3: authmethod_is_enabled gssapi-keyex debug1: Next authentication method: gssapi-keyex debug1: No valid Key exchange context debug2: we did not send a packet, disable method debug3: authmethod_lookup gssapi-with-mic debug3: remaining preferred: publickey,keyboard-interactive,password debug3: authmethod_is_enabled gssapi-with-mic debug1: Next authentication method: gssapi-with-mic debug1: Unspecified GSS failure. Minor code may provide more information No Kerberos credentials available debug1: Unspecified GSS failure. Minor code may provide more information No Kerberos credentials available debug1: Unspecified GSS failure. Minor code may provide more information debug1: Unspecified GSS failure. Minor code may provide more information No Kerberos credentials available debug2: we did not send a packet, disable method 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: /home/ir_comp_N232/.ssh/id_rsa debug3: send_pubkey_test debug2: we sent a publickey packet, wait for reply debug1: Server accepts key: pkalg ssh-rsa blen 279 debug2: input_userauth_pk_ok: fp 11:4a:69:3f:dc:51:40:cf:b4:0d:8a:29:0b:8f:80:2d debug3: sign_and_send_pubkey: RSA 11:4a:69:3f:dc:51:40:cf:b4:0d:8a:29:0b:8f:80:2d debug1: Authentication succeeded (publickey). Authenticated to 192.168.1.192 ([192.168.1.192]: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: 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 XDG_GREETER_DATA_DIR debug3: Ignored env SELINUX_INIT debug3: Ignored env VIRTUALENVWRAPPER_PROJECT_FILENAME debug3: Ignored env VIRTUALENVWRAPPER_SCRIPT debug3: Ignored env CLUTTER_IM_MODULE debug3: Ignored env SESSION debug3: Ignored env GPG_AGENT_INFO debug3: Ignored env TERM debug3: Ignored env VTE_VERSION debug3: Ignored env XDG_MENU_PREFIX debug3: Ignored env SHELL debug3: Ignored env WINDOWID debug3: Ignored env UPSTART_SESSION debug3: Ignored env GNOME_KEYRING_CONTROL debug3: Ignored env GTK_MODULES debug3: Ignored env NO_PROXY debug3: Ignored env USER debug3: Ignored env LD_LIBRARY_PATH debug3: Ignored env XDG_SESSION_PATH debug3: Ignored env XDG_SEAT_PATH debug3: Ignored env SSH_AUTH_SOCK debug3: Ignored env DEFAULTS_PATH debug3: Ignored env SESSION_MANAGER debug3: Ignored env WORKON_HOME debug3: Ignored env XDG_CONFIG_DIRS debug3: Ignored env VIRTUALENVWRAPPER_PYTHON debug3: Ignored env DESKTOP_SESSION debug3: Ignored env PATH debug3: Ignored env QT_IM_MODULE debug3: Ignored env VIRTUALENVWRAPPER_HOOK_DIR debug3: Ignored env QT_QPA_PLATFORMTHEME debug3: Ignored env PWD debug3: Ignored env JOB debug3: Ignored env XMODIFIERS debug3: Ignored env GNOME_KEYRING_PID debug1: Sending env LANG = en_IN debug2: channel 0: request env confirm 0 debug3: Ignored env GDM_LANG debug3: Ignored env MANDATORY_PATH debug3: Ignored env COMPIZ_CONFIG_PROFILE debug3: Ignored env IM_CONFIG_PHASE debug3: Ignored env GDMSESSION debug3: Ignored env SESSIONTYPE debug3: Ignored env SHLVL debug3: Ignored env HOME debug3: Ignored env XDG_SEAT debug3: Ignored env LANGUAGE debug3: Ignored env no_proxy debug3: Ignored env GNOME_DESKTOP_SESSION_ID debug3: Ignored env LOGNAME debug3: Ignored env COMPIZ_BIN_PATH debug3: Ignored env DBUS_SESSION_BUS_ADDRESS debug3: Ignored env XDG_DATA_DIRS debug3: Ignored env QT4_IM_MODULE debug3: Ignored env VIRTUALENVWRAPPER_WORKON_CD debug3: Ignored env INSTANCE debug3: Ignored env TEXTDOMAIN debug3: Ignored env XDG_RUNTIME_DIR debug3: Ignored env DISPLAY debug3: Ignored env XDG_CURRENT_DESKTOP debug3: Ignored env GTK_IM_MODULE debug3: Ignored env TEXTDOMAINDIR debug3: Ignored env XAUTHORITY debug3: Ignored env COLORTERM 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

Though I could see the errors related to RSA key, the machine eventually logs into the server, post which it hangs.

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  • You say "seconds", do you really mean "seconds"? And are you active during that time or does it hang after a short inactivity time? Commented Apr 4, 2018 at 13:29
  • Have you tried to increase verbosity of SSH (-vvv) ? What was the output? Commented Apr 5, 2018 at 7:06
  • @Broco Yes, I mean 'seconds'. I am active and could pass on commands like ls -l, df -h, etc., Commented Apr 5, 2018 at 9:31
  • @JaroslavKucera have added the verbose debug output. Though I could see there is a RSA key problem, I am able to log into the server. The problem occurs only after that. Commented Apr 5, 2018 at 9:36
  • @Apricot Look at the tcpdump -pnni eth0 on the remote server from a separate putty session, while trying the problem scenario. Commented Apr 5, 2018 at 9:39

1 Answer 1

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Disable GSSAPI, PAM and any other authentication method except publickey. You're not using Kerberos. Try it on a high port (2222) if you can't on the current. The idea is to get right to pubkey auth and remove any doubt the delay is due to the time the other methods are being tried. You can also play with the client order of auth choices

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