I have a Debian 9 host. I can ssh into my Raspberry Pi and other servers with no issue. I have openSUSE installed as a virtual machine in VirtualBox. I can ssh into that virtual machine with no issue. To set this up in VirtualBox, I went to: Settings > Network > Advanced > Port Forwarding > Name: ssh, Protocol: TCP, Host IP: (blank), Host Port: (random high port number), Guest IP: (blank), Guest Port: 22. This is for Adapter 1 and it is Attached to: NAT. These instructions are on a few different forum posts. I have done the same thing for my CentOS virtual machine but with a different Host Port (random high port number). I have made sure the sshd service is running with sudo systemctl status sshd. However, I am unable to ssh into the CentOS virtual machine. I receive the following error (last line below):~$ ssh -p 1820 CentosUser@127.0.0.1 -vOpenSSH_7.4p1 Debian-10, OpenSSL 1.0.2k  26 Jan 2017debug1: Reading configuration data /etc/ssh/ssh_configdebug1: /etc/ssh/ssh_config line 19: Applying options for *debug1: Connecting to 127.0.0.1 [127.0.0.1] port 1820.debug1: Connection established.debug1: key_load_public: No such file or directorydebug1: identity file /home/brock/.ssh/id_rsa type -1debug1: key_load_public: No such file or directorydebug1: identity file /home/brock/.ssh/id_rsa-cert type -1debug1: key_load_public: No such file or directorydebug1: identity file /home/brock/.ssh/id_dsa type -1debug1: key_load_public: No such file or directorydebug1: identity file /home/brock/.ssh/id_dsa-cert type -1debug1: key_load_public: No such file or directorydebug1: identity file /home/brock/.ssh/id_ecdsa type -1debug1: key_load_public: No such file or directorydebug1: identity file /home/brock/.ssh/id_ecdsa-cert type -1debug1: key_load_public: No such file or directorydebug1: identity file /home/brock/.ssh/id_ed25519 type -1debug1: key_load_public: No such file or directorydebug1: identity file /home/brock/.ssh/id_ed25519-cert type -1debug1: Enabling compatibility mode for protocol 2.0debug1: Local version string SSH-2.0-OpenSSH_7.4p1 Debian-10ssh_exchange_identification: read: Connection reset by peerThe issue has to do with how CentOS is configured for its networking or ssh. The CentOS VM has no issue connecting to the internet. It seems this could be an easy test for someone with VirtualBox. The CentOS minimal iso is 680 MB.Here is the /var/log/secure output for today when I've tried to ssh in with both my user and root.May 31 00:58:03 localhost sshd[1141]: Server listening on 0.0.0.0 port 22.May 31 00:58:03 localhost sshd[1141]: Server listening on :: port 22.May 31 00:58:14 localhost login: pam_unix(login:session): session opened for user root by LOGIN(uid=0)May 31 00:58:14 localhost login: ROOT LOGIN ON tty1May 31 00:58:22 localhost polkitd[656]: Registered Authentication Agent for unix-process:2529:3738 (system bus name :1.30 [/usr/bin/pkttyagent --notify-fd 5 --fallback], object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale en_US.UTF-8)May 31 00:58:23 localhost login: pam_unix(login:session): session closed for user rootMay 31 00:58:23 localhost polkitd[656]: Unregistered Authentication Agent for unix-process:2529:3738 (system bus name :1.30, object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale en_US.UTF-8) (disconnected from bus)May 31 00:58:25 localhost gdm-launch-environment]: pam_unix(gdm-launch-environment:session): session opened for user gdm by (uid=0)May 31 00:58:27 localhost polkitd[656]: Registered Authentication Agent for unix-session:c1 (system bus name :1.55 [gnome-shell --mode=gdm], object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale en_US.UTF-8)May 31 00:58:39 localhost gdm-password]: pam_unix(gdm-password:session): session opened for user jbc by (unknown)(uid=0)May 31 00:58:40 localhost gdm-launch-environment]: pam_unix(gdm-launch-environment:session): session closed for user gdmMay 31 00:58:40 localhost polkitd[656]: Unregistered Authentication Agent for unix-session:c1 (system bus name :1.55, object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale en_US.UTF-8) (disconnected from bus)May 31 00:58:40 localhost polkitd[656]: Registered Authentication Agent for unix-session:2 (system bus name :1.69 [/usr/libexec/xfce-polkit], object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale en_US.UTF-8)May 31 00:59:30 localhost sudo:     jbc : user NOT in sudoers ; TTY=pts/0 ; PWD=/home/jbc ; USER=root ; COMMAND=/bin/yum remove --purge chromiumMay 31 00:59:42 localhost su: pam_unix(su-l:session): session opened for user root by jbc(uid=1000)May 31 01:15:18 localhost polkitd[656]: Registered Authentication Agent for unix-process:4582:105315 (system bus name :1.86 [/usr/bin/pkttyagent --notify-fd 5 --fallback], object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale en_US.UTF-8)May 31 12:58:19 localhost polkitd[659]: Loading rules from directory /etc/polkit-1/rules.dMay 31 12:58:19 localhost polkitd[659]: Loading rules from directory /usr/share/polkit-1/rules.dMay 31 12:58:19 localhost polkitd[659]: Finished loading, compiling and executing 4 rulesMay 31 12:58:19 localhost polkitd[659]: Acquired the name org.freedesktop.PolicyKit1 on the system busMay 31 12:58:29 localhost sshd[1139]: Server listening on 0.0.0.0 port 22.May 31 12:58:29 localhost sshd[1139]: Server listening on :: port 22.May 31 12:58:52 localhost login: pam_unix(login:session): session opened for user jbc by LOGIN(uid=0)May 31 12:58:52 localhost login: LOGIN ON tty1 BY jbcMay 31 13:02:01 localhost polkitd[659]: Registered Authentication Agent for unix-process:2581:22909 (system bus name :1.34 [/usr/bin/pkttyagent --notify-fd 5 --fallback], object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale en_US.UTF-8)May 31 13:02:04 localhost polkitd[659]: Operator of unix-process:2581:22909 successfully authenticated as unix-user:root to gain TEMPORARY authorization for action org.freedesktop.systemd1.manage-units for system-bus-name::1.35 [init 5] (owned by unix-user:jbc)May 31 13:02:05 localhost polkitd[659]: Unregistered Authentication Agent for unix-process:2581:22909 (system bus name :1.34, object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale en_US.UTF-8) (disconnected from bus)May 31 13:02:05 localhost login: pam_unix(login:session): session closed for user jbcMay 31 13:02:06 localhost gdm-launch-environment]: pam_unix(gdm-launch-environment:session): session opened for user gdm by (uid=0)May 31 13:02:09 localhost polkitd[659]: Registered Authentication Agent for unix-session:c1 (system bus name :1.64 [gnome-shell --mode=gdm], object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale en_US.UTF-8)May 31 13:02:15 localhost gdm-password]: pam_unix(gdm-password:session): session opened for user jbc by (unknown)(uid=0)May 31 13:02:16 localhost gdm-launch-environment]: pam_unix(gdm-launch-environment:session): session closed for user gdmMay 31 13:02:16 localhost polkitd[659]: Unregistered Authentication Agent for unix-session:c1 (system bus name :1.64, object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale en_US.UTF-8) (disconnected from bus)May 31 13:02:17 localhost polkitd[659]: Registered Authentication Agent for unix-session:4 (system bus name :1.78 [/usr/libexec/xfce-polkit], object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale en_US.UTF-8)May 31 13:02:33 localhost su: pam_unix(su-l:session): session opened for user root by jbc(uid=1000)May 31 13:03:18 localhost polkitd[659]: Registered Authentication Agent for unix-process:4348:30623 (system bus name :1.87 [/usr/bin/pkttyagent --notify-fd 5 --fallback], object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale en_US.UTF-8)May 31 13:03:18 localhost polkitd[659]: Unregistered Authentication Agent for unix-process:4348:30623 (system bus name :1.87, object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale en_US.UTF-8) (disconnected from bus)Also, /var/log/secure ssh related:[root@localhost ~]# cat /var/log/secure | grep May 31 | grep sshMay 31 00:58:03 localhost sshd[1141]: Server listening on 0.0.0.0 port 22.May 31 00:58:03 localhost sshd[1141]: Server listening on :: port 22.May 31 12:58:29 localhost sshd[1139]: Server listening on 0.0.0.0 port 22.May 31 12:58:29 localhost sshd[1139]: Server listening on :: port 22.
Cannot ssh into VirtualBox CentOS 7 guest from Debian host
centos;ssh;virtualbox;sshd