openssh seamless login does not work - linux

Question

Have been trying to setup the seamless ssh login across couple of servers but running into issues as after copying the public key the ssh to the host still asks for the password. Here is what I did
[root#app6 .ssh]# ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
/root/.ssh/id_rsa already exists.
Overwrite (y/n)? y
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
e9:e9:b4:e5:50:7b:9b:f6:3f:d5:65:52:39:9c:ba:38 root#app6
The key's randomart image is:
+--[ RSA 2048]----+
| . o|
| =.|
| ...|
| . .. o|
| S . . .oo|
| . o E . o|
| = o o .|
| o = ..o . |
| o ..o...o|
+-----------------+
And then copied the id to the host
[root#app6 .ssh]# ssh-copy-id app3
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
\S
Kernel \r on an \m
Password:
Number of key(s) added: 1
Now try logging into the machine, with: "ssh 'app3'"
and check to make sure that only the key(s) you wanted were added.
But when I try to login then it does not work (asks for password) –
[root#app6 .ssh]# ssh 'app3'
\S
Kernel \r on an \m
Password:
I should not be seeing the 'Password:' prompt. Apparently something is amiss.
Here is the version of ssh that is running:
[root#app6 ~]# ssh -V
OpenSSH_6.6.1p1, OpenSSL 1.0.1e-fips 11 Feb 2013
Adding the output of ssh -vvv app3 below:
debug3: load_hostkeys: loading entries for host "172.27.36.104" from file "/root/.ssh/known_hosts"
debug3: load_hostkeys: found key type ECDSA in file /root/.ssh/known_hosts:5
debug3: load_hostkeys: loaded 1 keys
debug1: Host '172.27.36.104' is known and matches the ECDSA host key.
debug1: Found key in /root/.ssh/known_hosts:5
debug1: ssh_ecdsa_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: /root/.ssh/id_rsa (0x7f471042f250),
debug2: key: /root/.ssh/id_dsa ((nil)),
debug2: key: /root/.ssh/id_ecdsa (0x7f4710433730),
debug2: key: /root/.ssh/id_ed25519 ((nil)),
debug3: input_userauth_banner
\S
Kernel \r on an \m
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password,keyboard-interactive
debug3: start over, passed a different list publickey,gssapi-keyex,gssapi-with-mic,password,keyboard-interactive
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: /root/.ssh/id_rsa
debug3: send_pubkey_test
debug2: we sent a publickey packet, wait for reply
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password,keyboard-interactive
debug1: Trying private key: /root/.ssh/id_dsa
debug3: no such identity: /root/.ssh/id_dsa: No such file or directory
debug1: Offering ECDSA public key: /root/.ssh/id_ecdsa
debug3: send_pubkey_test
debug2: we sent a publickey packet, wait for reply
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password,keyboard-interactive
debug1: Trying private key: /root/.ssh/id_ed25519
debug3: no such identity: /root/.ssh/id_ed25519: No such file or directory
debug2: we did not send a packet, disable method
debug3: authmethod_lookup keyboard-interactive
debug3: remaining preferred: password
debug3: authmethod_is_enabled keyboard-interactive
debug1: Next authentication method: keyboard-interactive
debug2: userauth_kbdint
debug2: we sent a keyboard-interactive packet, wait for reply
debug2: input_userauth_info_req
debug2: input_userauth_info_req: num_prompts 1
Password:

Answer 1

Check the following
The directory app3:~/.ssh has permissions 0700
The file app3:~/.ssh/authorized_keys has permissions 0600
The key app6:~/.ssh/id_rsa.pub exists in app3:~/.ssh/authorized_keys
Check sshd config file
PermitRootLogin yes
RSAAuthentication yes
PubkeyAuthentication yes
If all the above is correct, then run ssh -vvv app3 to see a very verbose connection info. It should provide feedback on why the password-less login fails.

Answer 2

comment for #yk11 's answer:
4.check the sshd config file
PermitRootLogin yes
RSAAuthentication yes
PubkeyAuthentication yes
open these config and restart sshd process.