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The server is running CentOS 7 and using OpenSSH. The client is running OpenSSH too.

To set up key-based authentication from the server to the client, I generated a new SSH keypair using the command: ssh-keygen

Then I used the ssh-copy-id utility to copy my public key over to the authorized_keys file: ssh-copy-id -i /var/spool/centreon/.ssh/id_rsa.pub centreon@194.30.1.34

As I expected, the utility asked for the password in order to complete the public key transfer. When all was done, I attempted to login. It should have let me through without requiring a password: ssh centreon@194.30.1.34

But I kept getting prompted for a password.

• I checked my authorized_keys file over on the client to make sure my
  public key had been copied over correctly. Check.


• I made sure that the file was read-write only for myself and none
  others. Check.


• I made sure that the following options were enabled in
  /etc/ssh/sshd_config: PubkeyAuthentication yes and AuthorizedKeysFile .ssh/authorized_keys. Check.

Still, I kept getting prompted for a password.

This is the output of ssh centreon@194.30.1.34 -vv:

debug2: resolving "194.30.1.34" port 22

debug2: ssh_connect_direct: needpriv 0

debug1: Connecting to 194.30.1.34 [194.30.1.34] port 22.

debug1: Connection established.

debug1: identity file /var/spool/centreon/.ssh/id_rsa type 1

debug1: key_load_public: No such file or directory

debug1: identity file /var/spool/centreon/.ssh/id_rsa-cert type -1

debug1: key_load_public: No such file or directory

debug1: identity file /var/spool/centreon/.ssh/id_dsa type -1

debug1: key_load_public: No such file or directory

debug1: identity file /var/spool/centreon/.ssh/id_dsa-cert type -1

debug1: key_load_public: No such file or directory

debug1: identity file /var/spool/centreon/.ssh/id_ecdsa type -1

debug1: key_load_public: No such file or directory

debug1: identity file /var/spool/centreon/.ssh/id_ecdsa-cert type -1

debug1: key_load_public: No such file or directory

debug1: identity file /var/spool/centreon/.ssh/id_ed25519 type -1

debug1: key_load_public: No such file or directory

debug1: identity file /var/spool/centreon/.ssh/id_ed25519-cert type -1

debug1: Enabling compatibility mode for protocol 2.0

debug1: Local version string SSH-2.0-OpenSSH_7.4

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 194.30.1.34:22 as 'centreon'

debug1: SSH2_MSG_KEXINIT sent

debug1: SSH2_MSG_KEXINIT received

debug2: local client KEXINIT proposal

debug2: KEX algorithms: curve25519-sha256,curve25519-sha256@libssh.org,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,ext-info-c

debug2: host key algorithms: ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-ed25519-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa,ssh-dss

debug2: ciphers ctos: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-cbc,aes192-cbc,aes256-cbc

debug2: ciphers stoc: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-cbc,aes192-cbc,aes256-cbc

debug2: MACs ctos: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1

debug2: MACs stoc: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1

debug2: compression ctos: none,zlib@openssh.com,zlib

debug2: compression stoc: none,zlib@openssh.com,zlib

debug2: languages ctos:

debug2: languages stoc:

debug2: first_kex_follows 0

debug2: reserved 0

debug2: peer server KEXINIT proposal

debug2: KEX algorithms: curve25519-sha256,curve25519-sha256@libssh.org,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: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-cbc,aes192-cbc,blowfish-cbc,cast128-cbc,3des-cbc

debug2: ciphers stoc: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-cbc,aes192-cbc,blowfish-cbc,cast128-cbc,3des-cbc

debug2: MACs ctos: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1

debug2: MACs stoc: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1

debug2: compression ctos: none,zlib@openssh.com

debug2: compression stoc: none,zlib@openssh.com

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: chacha20-poly1305@openssh.com MAC: <implicit> compression: none

debug1: kex: client->server cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none

debug1: kex: curve25519-sha256 need=64 dh_need=64

debug1: kex: curve25519-sha256 need=64 dh_need=64

debug1: expecting SSH2_MSG_KEX_ECDH_REPLY

debug1: Server host key: ecdsa-sha2-nistp256 SHA256:5dqMvnfs9E33X/fn4ss+Ib4RiBQxiz634IAIB2rzo/U

debug1: Host '194.30.1.34' is known and matches the ECDSA host key.

debug1: Found key in /var/spool/centreon/.ssh/known_hosts:1

debug2: set_newkeys: mode 1

debug1: rekey after 134217728 blocks

debug1: SSH2_MSG_NEWKEYS sent

debug1: expecting SSH2_MSG_NEWKEYS

debug1: SSH2_MSG_NEWKEYS received

debug2: set_newkeys: mode 0

debug1: rekey after 134217728 blocks

debug2: key: /var/spool/centreon/.ssh/id_rsa (0x55b36eff6320)

debug2: key: /var/spool/centreon/.ssh/id_dsa ((nil))

debug2: key: /var/spool/centreon/.ssh/id_ecdsa ((nil))

debug2: key: /var/spool/centreon/.ssh/id_ed25519 ((nil))

debug2: service_accept: ssh-userauth

debug1: SSH2_MSG_SERVICE_ACCEPT received

debug1: Authentications that can continue: gssapi-keyex,gssapi-with-mic,password

debug1: Next authentication method: password

It seems is not using publickey method, but it is activated on sshd_config file.

I tried with ssh -o PreferredAuthentications=publickey centreon@194.30.1.34 but it doesn't work.

# /usr/sbin/sshd -d

debug1: sshd version OpenSSH_7.4, OpenSSL 1.0.2k-fips  26 Jan 2017

debug1: private host key #0: ssh-rsa SHA256:hrLms1qzSG4kzJWoYHSNRCqU4rT8D1MD6zBc                                                                              NRcG3cQ

debug1: private host key #1: ecdsa-sha2-nistp256 SHA256:TxOu5pzDEA/jneXetbsvo0w0                                                                              lljcnaftCo+ttHGmksE

debug1: private host key #2: ssh-ed25519 SHA256:/B/n9JLWYa0TDCsXERy7riYynqnPppsC                                                                              CKRPLIhmr9o

debug1: rexec_argv[0]='/usr/sbin/sshd'

debug1: rexec_argv[1]='-d'

debug1: Set /proc/self/oom_score_adj from 0 to -1000

debug1: Bind to port 22 on 0.0.0.0.

Server listening on 0.0.0.0 port 22.

debug1: Bind to port 22 on ::.

Server listening on :: port 22.

debug1: Server will not fork when running in debugging mode.

debug1: rexec start in 5 out 5 newsock 5 pipe -1 sock 8

debug1: inetd sockets after dupping: 3, 3

Connection from 212.81.200.106 port 48632 on 192.168.1.18 port 22

debug1: Client protocol version 2.0; client software version OpenSSH_7.4

debug1: match: OpenSSH_7.4 pat OpenSSH* compat 0x04000000

debug1: Local version string SSH-2.0-OpenSSH_7.4

debug1: Enabling compatibility mode for protocol 2.0

debug1: SELinux support disabled [preauth]

debug1: permanently_set_uid: 74/74 [preauth]

debug1: list_hostkey_types: ssh-rsa,rsa-sha2-512,rsa-sha2-256,ecdsa-sha2-nistp25                                                                              6,ssh-ed25519 [preauth]

debug1: SSH2_MSG_KEXINIT sent [preauth]

debug1: SSH2_MSG_KEXINIT received [preauth]

debug1: kex: algorithm: curve25519-sha256 [preauth]

debug1: kex: host key algorithm: ecdsa-sha2-nistp256 [preauth]

debug1: kex: client->server cipher: chacha20-poly1305@openssh.com MAC: <implicit                                                                              > compression: none [preauth]

debug1: kex: server->client cipher: chacha20-poly1305@openssh.com MAC: <implicit                                                                              > compression: none [preauth]

debug1: kex: curve25519-sha256 need=64 dh_need=64 [preauth]

debug1: kex: curve25519-sha256 need=64 dh_need=64 [preauth]

debug1: expecting SSH2_MSG_KEX_ECDH_INIT [preauth]

debug1: rekey after 134217728 blocks [preauth]

debug1: SSH2_MSG_NEWKEYS sent [preauth]

debug1: expecting SSH2_MSG_NEWKEYS [preauth]

debug1: SSH2_MSG_NEWKEYS received [preauth]

debug1: rekey after 134217728 blocks [preauth]

debug1: KEX done [preauth]

debug1: userauth-request for user centreon service ssh-connection method none [p                                                                              reauth]

debug1: attempt 0 failures 0 [preauth]

debug1: PAM: initializing for "centreon"

debug1: PAM: setting PAM_RHOST to "yoshimura.ibex.es"

debug1: PAM: setting PAM_TTY to "ssh"