Permission denied (publickey).

[jagiella]

I am trying to connect to a remote server via a keyfile with password. The connection failes with the following log output:

Jan 15 17:19:08 LOCAL_HOST NetworkManager[962]: <info>  [1610727548.6701] audit: op="connection-activate" uuid="e23451e6-0932-4e9f-a277-f255076d292a" name="VPN 1" pid=66592 uid=1000 result="success"
Jan 15 17:19:08 LOCAL_HOST NetworkManager[962]: <info>  [1610727548.6746] vpn-connection[0x556a60f5c110,e23451e6-0932-4e9f-a277-f255076d292a,"VPN 1",0]: Started the VPN service, PID 88366
Jan 15 17:19:08 LOCAL_HOST NetworkManager[962]: <info>  [1610727548.6826] vpn-connection[0x556a60f5c110,e23451e6-0932-4e9f-a277-f255076d292a,"VPN 1",0]: Saw the service appear; activating connection
Jan 15 17:19:08 LOCAL_HOST NetworkManager[962]: <info>  [1610727548.6911] vpn-connection[0x556a60f5c110,e23451e6-0932-4e9f-a277-f255076d292a,"VPN 1",0]: VPN connection: (ConnectInteractive) reply received
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: Error getting ssh-agent socket ownership: 14
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: Using root's .ssh/known_hosts
Jan 15 17:19:08 LOCAL_HOST NetworkManager[88371]: sh: 1: Syntax error: Bad fd number
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: ssh started with pid 88372
Jan 15 17:19:08 LOCAL_HOST NetworkManager[962]: <info>  [1610727548.6928] vpn-connection[0x556a60f5c110,e23451e6-0932-4e9f-a277-f255076d292a,"VPN 1",0]: VPN plugin: state changed: starting (3)
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: OpenSSH_8.2p1 Ubuntu-4ubuntu0.1, OpenSSL 1.1.1f  31 Mar 2020
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: Reading configuration data /etc/ssh/ssh_config
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: /etc/ssh/ssh_config line 19: include /etc/ssh/ssh_config.d/*.conf matched no files
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: /etc/ssh/ssh_config line 21: Applying options for *
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: Connecting to REMOTE_HOST [REMOTE_IP] port PORT.
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: Connection established.
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: identity file /home/USERNAME/.ssh/id_rsa type 0
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: identity file /home/USERNAME/.ssh/id_rsa-cert type -1
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: Local version string SSH-2.0-OpenSSH_8.2p1 Ubuntu-4ubuntu0.1
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: Remote protocol version 2.0, remote software version OpenSSH_8.2p1 Ubuntu-4ubuntu0.1
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: match: OpenSSH_8.2p1 Ubuntu-4ubuntu0.1 pat OpenSSH* compat 0x04000000
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: Authenticating to REMOTE_HOST:PORT as 'USERNAME'
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: SSH2_MSG_KEXINIT sent
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: SSH2_MSG_KEXINIT received
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: kex: algorithm: curve25519-sha256
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: kex: host key algorithm: ecdsa-sha2-nistp256
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: kex: server->client cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: kex: client->server cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: Server host key: ecdsa-sha2-nistp256 SHA256:YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: Host '[REMOTE_HOST]:PORT' is known and matches the ECDSA host key.
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: Found key in /root/.ssh/known_hosts:1
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: Failed to add the ECDSA host key for IP address '[REMOTE_IP]:PORT' to the list of known hosts (/root/.ssh/known_hosts).
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: rekey out after 134217728 blocks
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: SSH2_MSG_NEWKEYS sent
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: expecting SSH2_MSG_NEWKEYS
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: SSH2_MSG_NEWKEYS received
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: rekey in after 134217728 blocks
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: Will attempt key: /home/USERNAME/.ssh/id_rsa RSA SHA256:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX explicit
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: SSH2_MSG_EXT_INFO received
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: kex_input_ext_info: server-sig-algs=<ssh-ed25519,sk-ssh-ed25519@openssh.com,ssh-rsa,rsa-sha2-256,rsa-sha2-512,ssh-dss,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,sk-ecdsa-sha2-nistp256@openssh.com>
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: SSH2_MSG_SERVICE_ACCEPT received
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: Authentications that can continue: publickey
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: Next authentication method: publickey
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: Offering public key: /home/USERNAME/.ssh/id_rsa RSA SHA256:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX explicit
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: Server accepts key: /home/USERNAME/.ssh/id_rsa RSA SHA256:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX explicit
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: debug1: No more authentication methods to try.
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: USERNAME@REMOTE_HOST: Permission denied (publickey).
Jan 15 17:19:08 LOCAL_HOST nm-ssh-service[88366]: ssh exited with error code 255
Jan 15 17:19:08 LOCAL_HOST NetworkManager[962]: <warn>  [1610727548.9993] vpn-connection[0x556a60f5c110,e23451e6-0932-4e9f-a277-f255076d292a,"VPN 1",0]: VPN plugin: failed: connect-failed (1)
Jan 15 17:19:08 LOCAL_HOST NetworkManager[962]: <warn>  [1610727548.9993] vpn-connection[0x556a60f5c110,e23451e6-0932-4e9f-a277-f255076d292a,"VPN 1",0]: VPN plugin: failed: connect-failed (1)
Jan 15 17:19:08 LOCAL_HOST NetworkManager[962]: <info>  [1610727548.9993] vpn-connection[0x556a60f5c110,e23451e6-0932-4e9f-a277-f255076d292a,"VPN 1",0]: VPN plugin: state changed: stopping (5)
Jan 15 17:19:08 LOCAL_HOST NetworkManager[962]: <info>  [1610727548.9994] vpn-connection[0x556a60f5c110,e23451e6-0932-4e9f-a277-f255076d292a,"VPN 1",0]: VPN plugin: state changed: stopped (6)

LOCAL_HOST, REMOTE_HOST, REMOTE_IP, PORT, USERNAME, XXXXXXX and YYYYYYY are placeholders for privacy reasons ;)

I also tried ssh-agent, but with similar results.