I have a problem when establishing an ssh session, either tunnel only (-N) or when starting a console. My client is 18.04.2 LTS and my server is CentOs 7. The behavior seems random
- Sometimes the session starts successfully
- Sometimes it hangs on : (debug2: we sent a publickey packet, wait for reply)
- Sometimes it hangs in : (debug3: send packet: type 50) after server accepts key
It is so frustrating and random. What could be wrong? The following is a sample of the output when it hangs on (send packet: type 50) after the server accepts key.
$ ssh -vvv OpenSSH_7.6p1 Ubuntu-4ubuntu0.2, OpenSSL 1.0.2n 7 Dec 2017 debug1: Reading configuration data /home/parsa/.ssh/config debug1: Reading configuration data /etc/ssh/ssh_config debug1: /etc/ssh/ssh_config line 19: Applying options for * debug2: resolving "XX.XX.XXX.XX" port 22 debug2: ssh_connect_direct: needpriv 0 debug1: Connecting to XX.XX.XXX.XX [XX.XX.XXX.XX] port 22. debug1: Connection established. debug1: identity file /home/parsa/.ssh/id_rsa type 0 debug1: key_load_public: No such file or directory debug1: identity file /home/parsa/.ssh/id_rsa-cert type -1 debug1: key_load_public: No such file or directory debug1: identity file /home/parsa/.ssh/id_dsa type -1 debug1: key_load_public: No such file or directory debug1: identity file /home/parsa/.ssh/id_dsa-cert type -1 debug1: key_load_public: No such file or directory debug1: identity file /home/parsa/.ssh/id_ecdsa type -1 debug1: key_load_public: No such file or directory debug1: identity file /home/parsa/.ssh/id_ecdsa-cert type -1 debug1: key_load_public: No such file or directory debug1: identity file /home/parsa/.ssh/id_ed25519 type -1 debug1: key_load_public: No such file or directory debug1: identity file /home/parsa/.ssh/id_ed25519-cert type -1 debug1: Local version string SSH-2.0-OpenSSH_7.6p1 Ubuntu-4ubuntu0.2 debug1: Remote protocol version 2.0, remote software version OpenSSH_7.4 debug1: match: OpenSSH_7.4 pat OpenSSH* compat 0x04000000 debug2: fd 3 setting O_NONBLOCK debug1: Authenticating to XX.XX.XXX.XX:22 as 'parsa' debug3: hostkeys_foreach: reading file "/home/parsa/.ssh/known_hosts" debug3: record_hostkey: found key type ECDSA in file /home/parsa/.ssh/known_hosts:1 debug3: load_hostkeys: loaded 1 keys from XX.XX.XXX.XX debug3: order_hostkeyalgs: prefer hostkeyalgs: ,,,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521 debug3: send packet: type 20 debug1: SSH2_MSG_KEXINIT sent debug3: receive packet: type 20 debug1: SSH2_MSG_KEXINIT received debug2: local client KEXINIT proposal debug2: KEX algorithms: curve25519-sha256,,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha256,diffie-hellman-group14-sha1,ext-info-c debug2: host key algorithms: ,,,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,,,ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa debug2: ciphers ctos: ,aes128-ctr,aes192-ctr,aes256-ctr,, debug2: ciphers stoc: ,aes128-ctr,aes192-ctr,aes256-ctr,, debug2: MACs ctos: ,,,,,,,hmac-sha2-256,hmac-sha2-512,hmac-sha1 debug2: MACs stoc: ,,,,,,,hmac-sha2-256,hmac-sha2-512,hmac-sha1 debug2: compression ctos: ,zlib,none debug2: compression stoc: ,zlib,none debug2: languages ctos: debug2: languages stoc: debug2: first_kex_follows 0 debug2: reserved 0 debug2: peer server KEXINIT proposal debug2: KEX algorithms: curve25519-sha256,,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha256,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1 debug2: host key algorithms: ssh-rsa,rsa-sha2-512,rsa-sha2-256,ecdsa-sha2-nistp256,ssh-ed25519 debug2: ciphers ctos: ,aes128-ctr,aes192-ctr,aes256-ctr,,,aes128-cbc,aes192-cbc,aes256-cbc,blowfish-cbc,cast128-cbc,3des-cbc debug2: ciphers stoc: ,aes128-ctr,aes192-ctr,aes256-ctr,,,aes128-cbc,aes192-cbc,aes256-cbc,blowfish-cbc,cast128-cbc,3des-cbc debug2: MACs ctos: ,,,,,,,hmac-sha2-256,hmac-sha2-512,hmac-sha1 debug2: MACs stoc: ,,,,,,,hmac-sha2-256,hmac-sha2-512,hmac-sha1 debug2: compression ctos: none, debug2: compression stoc: none, debug2: languages ctos: debug2: languages stoc: debug2: first_kex_follows 0 debug2: reserved 0 debug1: kex: algorithm: curve25519-sha256 debug1: kex: host key algorithm: ecdsa-sha2-nistp256 debug1: kex: server->client cipher: MAC: <implicit> compression: debug1: kex: client->server cipher: MAC: <implicit> compression: debug3: send packet: type 30 debug1: expecting SSH2_MSG_KEX_ECDH_REPLY debug3: receive packet: type 31 debug1: Server host key: ecdsa-sha2-nistp256 SHA256:PGifCzsbbBFaBbm3E2N7fQA70iyUO/mHGz5HQzPd3wc debug3: hostkeys_foreach: reading file "/home/parsa/.ssh/known_hosts" debug3: record_hostkey: found key type ECDSA in file /home/parsa/.ssh/known_hosts:1 debug3: load_hostkeys: loaded 1 keys from XX.XX.XXX.XX debug1: Host 'XX.XX.XXX.XX' is known and matches the ECDSA host key. debug1: Found key in /home/parsa/.ssh/known_hosts:1 debug3: send packet: type 21 debug2: set_newkeys: mode 1 debug1: rekey after 134217728 blocks debug1: SSH2_MSG_NEWKEYS sent debug1: expecting SSH2_MSG_NEWKEYS debug3: receive packet: type 21 debug1: SSH2_MSG_NEWKEYS received debug2: set_newkeys: mode 0 debug1: rekey after 134217728 blocks debug2: key: /home/parsa/.ssh/id_rsa (0x55a63fd78630), agent debug2: key: /home/parsa/.ssh/id_dsa ((nil)) debug2: key: /home/parsa/.ssh/id_ecdsa ((nil)) debug2: key: /home/parsa/.ssh/id_ed25519 ((nil)) debug3: send packet: type 5 debug3: receive packet: type 7 debug1: SSH2_MSG_EXT_INFO received debug1: kex_input_ext_info: server-sig-algs=<rsa-sha2-256,rsa-sha2-512> debug3: receive packet: type 6 debug2: service_accept: ssh-userauth debug1: SSH2_MSG_SERVICE_ACCEPT received debug3: send packet: type 50 debug3: receive packet: type 51 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 (default cache: FILE:/tmp/krb5cc_1000) debug1: Unspecified GSS failure. Minor code may provide more information No Kerberos credentials available (default cache: FILE:/tmp/krb5cc_1000) 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 public key: RSA SHA256:UmGbR0Po40l31qILYVQKTslfHxbbzXXUHU7/JPi/Fy4 /home/parsa/.ssh/id_rsa debug3: send_pubkey_test debug3: send packet: type 50 debug2: we sent a publickey packet, wait for reply debug3: receive packet: type 60 debug1: Server accepts key: pkalg rsa-sha2-512 blen 279 debug2: input_userauth_pk_ok: fp SHA256:UmGbR0Po40l31qILYVQKTslfHxbbzXXUHU7/JPi/Fy4 debug3: sign_and_send_pubkey: RSA SHA256:UmGbR0Po40l31qILYVQKTslfHxbbzXXUHU7/JPi/Fy4 debug3: send packet: type 50 
