I tried different solutions but none of them work.I generated a key with ssh-keygen on a machine. I add this key on a linux server in /root/.ssh/authorized_keys, and it works perfectly.On a second linux server, I did the same. But it doesn't work. I tried different things :Put my key in /root/.ssh/authorized_keys2Edited /etc/ssh/ssh_config and /etc/ssh/sshd_config (by commenting and uncommenting lines)Gave the right rights (700 to .ssh directory and 600 to authorized_keys files)Nothing seems to work... Still asking me a password.What could be the problem ?Thanks a lot.EDIT :`sshd_configPort 22# Use these options to restrict which interfaces/protocols sshd will bind to#ListenAddress ::#ListenAddress 0.0.0.0Protocol 2# HostKeys for protocol version 2HostKey /etc/ssh/ssh_host_rsa_key#HostKey /etc/ssh/ssh_host_dsa_key#HostKey /etc/ssh/ssh_host_ecdsa_keyHostKey /etc/ssh/ssh_host_ed25519_key#Privilege Separation is turned on for securityUsePrivilegeSeparation yes# Lifetime and size of ephemeral version 1 server keyKeyRegenerationInterval 3600ServerKeyBits 1024# LoggingSyslogFacility AUTHLogLevel INFO# Authentication:LoginGraceTime 120#PermitRootLogin without-passwordPermitRootLogin noStrictModes yesAllowUsers userRSAAuthentication yesPubkeyAuthentication yes#AuthorizedKeysFile     %h/.ssh/authorized_keys# Don't read the user's ~/.rhosts and ~/.shosts filesIgnoreRhosts yes# For this to work you will also need host keys in /etc/ssh_known_hostsRhostsRSAAuthentication no# similar for protocol version 2HostbasedAuthentication no# Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication#IgnoreUserKnownHosts yes# To enable empty passwords, change to yes (NOT RECOMMENDED)PermitEmptyPasswords no# Change to yes to enable challenge-response passwords (beware issues with# some PAM modules and threads)ChallengeResponseAuthentication no# Change to no to disable tunnelled clear text passwords#PasswordAuthentication yes# Kerberos options#KerberosAuthentication no#KerberosGetAFSToken no#KerberosOrLocalPasswd yes#KerberosTicketCleanup yes# GSSAPI options#GSSAPIAuthentication no#GSSAPICleanupCredentials yesX11Forwarding yesX11DisplayOffset 10PrintMotd noPrintLastLog yesTCPKeepAlive yes#UseLogin no#MaxStartups 10:30:60#Banner /etc/issue.net# Allow client to pass locale environment variablesAcceptEnv LANG LC_*Subsystem sftp /usr/lib/openssh/sftp-server# Set this to 'yes' to enable PAM authentication, account processing,# and session processing. If this is enabled, PAM authentication will# be allowed through the ChallengeResponseAuthentication and# PasswordAuthentication.  Depending on your PAM configuration,# PAM authentication via ChallengeResponseAuthentication may bypass# the setting of PermitRootLogin without-password.# If you just want the PAM account and session checks to run without# PAM authentication, then enable this but set PasswordAuthentication# and ChallengeResponseAuthentication to 'no'.UsePAM yesCiphers aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes128-ctrMACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,hmac-ripemd160KexAlgorithms diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1My ssh -vv resultOpenSSH_6.7p1 Debian-5+deb8u3, OpenSSL 1.0.1t  3 May 2016debug1: Reading configuration data /etc/ssh/ssh_configdebug1: /etc/ssh/ssh_config line 19: Applying options for *debug2: ssh_connect: needpriv 0debug1: Connecting to IP [IP] port 22.debug1: Connection established.debug1: permanently_set_uid: 0/0debug1: identity file /root/.ssh/id_rsa type 1debug1: key_load_public: No such file or directorydebug1: identity file /root/.ssh/id_rsa-cert type -1debug1: key_load_public: No such file or directorydebug1: identity file /root/.ssh/id_dsa type -1debug1: key_load_public: No such file or directorydebug1: identity file /root/.ssh/id_dsa-cert type -1debug1: key_load_public: No such file or directorydebug1: identity file /root/.ssh/id_ecdsa type -1debug1: key_load_public: No such file or directorydebug1: identity file /root/.ssh/id_ecdsa-cert type -1debug1: key_load_public: No such file or directorydebug1: identity file /root/.ssh/id_ed25519 type -1debug1: key_load_public: No such file or directorydebug1: identity file /root/.ssh/id_ed25519-cert type -1debug1: Enabling compatibility mode for protocol 2.0debug1: Local version string SSH-2.0-OpenSSH_6.7p1 Debian-5+deb8u3debug1: Remote protocol version 2.0, remote software version OpenSSH_6.7p1 Debian-5+deb8u3debug1: match: OpenSSH_6.7p1 Debian-5+deb8u3 pat OpenSSH* compat 0x04000000debug2: fd 3 setting O_NONBLOCKdebug1: SSH2_MSG_KEXINIT sentdebug1: SSH2_MSG_KEXINIT receiveddebug2: kex_parse_kexinit: curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1,diffie-hellman-group1-sha1debug2: kex_parse_kexinit: ssh-ed25519-cert-v01@openssh.com,ssh-ed25519,ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-rsa,ssh-dssdebug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com,chacha20-poly1305@openssh.com,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.sedebug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com,chacha20-poly1305@openssh.com,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,rijndael-cbc@lysator.liu.sedebug2: kex_parse_kexinit: 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,hmac-md5-etm@openssh.com,hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com,hmac-md5-96-etm@openssh.com,hmac-md5,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96debug2: kex_parse_kexinit: 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,hmac-md5-etm@openssh.com,hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com,hmac-md5-96-etm@openssh.com,hmac-md5,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96debug2: kex_parse_kexinit: none,zlib@openssh.com,zlibdebug2: kex_parse_kexinit: none,zlib@openssh.com,zlibdebug2: 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-group14-sha1,diffie-hellman-group-exchange-sha1debug2: kex_parse_kexinit: ssh-rsa,ssh-ed25519debug2: kex_parse_kexinit: aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes128-ctrdebug2: kex_parse_kexinit: aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes128-ctrdebug2: kex_parse_kexinit: hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,hmac-ripemd160debug2: kex_parse_kexinit: hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,hmac-ripemd160debug2: kex_parse_kexinit: none,zlib@openssh.comdebug2: kex_parse_kexinit: none,zlib@openssh.comdebug2: 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 umac-128-etm@openssh.comdebug1: kex: server->client aes128-ctr umac-128-etm@openssh.com nonedebug2: mac_setup: setup umac-128-etm@openssh.comdebug1: kex: client->server aes128-ctr umac-128-etm@openssh.com nonedebug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<3072<8192) sentdebug1: expecting SSH2_MSG_KEX_DH_GEX_GROUPdebug2: bits set: 1580/3072debug1: SSH2_MSG_KEX_DH_GEX_INIT sentdebug1: expecting SSH2_MSG_KEX_DH_GEX_REPLYdebug1: Server host key: ED25519 67:fd:fd:6e:a5:c1:32:96:9d:33:32:1a:cf:83:94:eadebug1: Host '[IP]:22' is known and matches the ED25519 host key.debug1: Found key in /root/.ssh/known_hosts:1debug2: bits set: 1546/3072debug2: kex_derive_keysdebug2: set_newkeys: mode 1debug1: SSH2_MSG_NEWKEYS sentdebug1: expecting SSH2_MSG_NEWKEYSdebug2: set_newkeys: mode 0debug1: SSH2_MSG_NEWKEYS receiveddebug1: SSH2_MSG_SERVICE_REQUEST sentdebug2: service_accept: ssh-userauthdebug1: SSH2_MSG_SERVICE_ACCEPT receiveddebug2: key: /root/.ssh/id_rsa (0x7f84b8ce74a0),debug2: key: /root/.ssh/id_dsa ((nil)),debug2: key: /root/.ssh/id_ecdsa ((nil)),debug2: key: /root/.ssh/id_ed25519 ((nil)),debug1: Authentications that can continue: publickey,passworddebug1: Next authentication method: publickeydebug1: Offering RSA public key: /root/.ssh/id_rsadebug2: we sent a publickey packet, wait for replydebug1: Authentications that can continue: publickey,passworddebug1: Trying private key: /root/.ssh/id_dsadebug1: Trying private key: /root/.ssh/id_ecdsadebug1: Trying private key: /root/.ssh/id_ed25519debug2: we did not send a packet, disable methoduser@IP's password:/var/log/auth.log (on the distant server)Jul 12 12:24:43 ns3111463 sshd[12971]: input_userauth_request: invalid user root [preauth]Jul 12 12:24:44 ns3111463 sshd[12971]: Connection closed by IP [preauth]Jul 12 12:24:46 ns3111463 sshd[12973]: Connection closed by IP [preauth]Jul 12 12:24:48 ns3111463 sshd[11787]: Received signal 15; terminating.Jul 12 12:24:48 ns3111463 sshd[12977]: Server listening on 0.0.0.0 port 22.Jul 12 12:24:48 ns3111463 sshd[12977]: Server listening on :: port 22.Jul 12 12:24:50 ns3111463 sshd[12978]: Connection closed by IP [preauth]Jul 12 12:24:51 ns3111463 sshd[12980]: User root from IP not allowed because not listed in AllowUsersJul 12 12:24:51 ns3111463 sshd[12980]: input_userauth_request: invalid user root [preauth]Jul 12 12:24:51 ns3111463 sshd[12980]: Connection closed by IP [preauth]Jul 12 12:25:49 ns3111463 sshd[12977]: Received signal 15; terminating.Jul 12 12:25:49 ns3111463 sshd[13029]: Server listening on 0.0.0.0 port 22.Jul 12 12:25:49 ns3111463 sshd[13029]: Server listening on :: port 22.Jul 12 12:25:50 ns3111463 sshd[13030]: User root from IP not allowed because not listed in AllowUsersJul 12 12:25:50 ns3111463 sshd[13030]: input_userauth_request: invalid user root [preauth]Jul 12 12:25:51 ns3111463 sshd[13030]: Connection closed by IP [preauth]Jul 12 12:25:53 ns3111463 sshd[13032]: Connection closed by IP [preauth]Jul 12 12:37:41 ns3111463 sshd[13552]: Connection closed by IP [preauth]Jul 12 12:38:09 ns3111463 sshd[13598]: Connection closed by IP [preauth]
Impossible to connect to server with ssh without password
linux;debian;ssh;sshd