why ssh always ask me for passwords even I have set the public key in VPS? - linux

Question

I just order a VPS in Vultr, and want set to ssh without passwords. after configured the ssh key things, I think it should be work, but failed.
yes, I have multiple ssh configures like github, gitlab or some other things and this is the configure file
Host gitlab
HostName cd.i.foo.com
IdentityFile ~/.ssh/id_rsa
Host github
HostName github.com
IdentityFile ~/.ssh/id_rsa_gayhub
Host vultr
HostName 198.13.59.103
Port 22
User root
IdentityFile ~/.ssh/id_rsa_vultr
but when I try with specified path ssh root#198.13.59.103 -i ~/.ssh/id_rsa_vultr, it can work!!!
below is some more log with ssh -v -v root#198.13.59.103
OpenSSH_7.6p1, LibreSSL 2.6.2
debug1: Reading configuration data /Users/xdguo/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 48: Applying options for *
debug1: Connecting to 198.13.59.103 port 22.
debug1: Connection established.
debug1: identity file /Users/xdguo/.ssh/id_rsa type 0
debug1: key_load_public: No such file or directory
debug1: identity file /Users/xdguo/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/xdguo/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/xdguo/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/xdguo/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/xdguo/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/xdguo/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/xdguo/.ssh/id_ed25519-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_7.6
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.2p2 Ubuntu-4ubuntu2.2
debug1: match: OpenSSH_7.2p2 Ubuntu-4ubuntu2.2 pat OpenSSH* compat 0x04000000
debug1: Authenticating to 198.13.59.103:22 as 'root'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: curve25519-sha256#libssh.org
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: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:s8qKj8CKXc6tp7zmVV32hiqHvdrxk46JVJQlQfpOQ0Q
debug1: Host '198.13.59.103' is known and matches the ECDSA host key.
debug1: Found key in /Users/xdguo/.ssh/known_hosts:40
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=<rsa-sha2-256,rsa-sha2-512>
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,password
debug1: Next authentication method: publickey
debug1: Offering public key: RSA SHA256:LBGwqZmXcUwd6kqIuDAxIj+jbPBeLbU1uwrxN1mQRKQ /Users/xdguo/.ssh/id_rsa
debug1: Authentications that can continue: publickey,password
debug1: Trying private key: /Users/xdguo/.ssh/id_dsa
debug1: Trying private key: /Users/xdguo/.ssh/id_ecdsa
debug1: Trying private key: /Users/xdguo/.ssh/id_ed25519
debug1: Next authentication method: password
root#198.13.59.103's password:
I think I spend lots of time here, it really maked me confused, thanks in advance for any help

Answer 1

ssh -v -v root#198.13.59.103 would not work, as it would default to id_rsa.
You need to test:
ssh -Tvv vultr
Only that "URL" (vultr) would be the equivalent of ssh root#198.13.59.103 -i ~/.ssh/id_rsa_vultr: it would find everything it needs in your ~/.ssh/config, under the Host vultr entry.

Answer 2

Doesn't look like it accepts an RSA-signed key.
Look at these lines:
debug1: Trying private key: /Users/xdguo/.ssh/id_dsa
debug1: Trying private key: /Users/xdguo/.ssh/id_ecdsa
debug1: Trying private key: /Users/xdguo/.ssh/id_ed25519
It's looking for a private key signed with DSA instead.
Try again and create a private-public pair signed with DSA instead. (No need to remove your other private key; you can have as many as you want of as many different types as you want on your machine.)