ssh: socket closed by remote peer

After a reboot, i can no longer connect to my Debian 10 server in SSH.

I receive the following error message: Socket is closed: Socket closed by remote peer

The identifier/password are correct (i don't use a key), I tried with Putty, ZenTermLite and Filezilla clients in sFTP mode.

    # log filezilla
    Status:      	Connecting to xx.xx.xx.xx...
    Response: 	fzSftp started, protocol_version=9
    Command:	open "root@xx.xx.xx.xx" 22
    Error:        	FATAL ERROR: Remote side unexpectedly closed network connection
    Error:        	Could not connect to server
    Status:      	Waiting to retry...

    # log ZenTermLite
    Socket is closed: Socket closed by remote peer

I do not have access to the server log since the connection is impossible.

Have you ever had a problem? Any idea how to fix it?

Thanks, regards.

**RESOLU**

 1. I restart in rescue mode
 2. [Mount the partition][1] containing the data
 3. Consult the `/var/log/syslog` file which indicates:

.

    @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
    @         WARNING: UNPROTECTED PRIVATE KEY FILE!          @
    @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
    Permissions 0755 for '/etc/ssh/ssh_host_ed25519_key' are too open.
    It is required that your private key files are NOT accessible by others.
    This private key will be ignored.
    Error loading host key "/etc/ssh/ssh_host_ed25519_key": bad permissions
    Could not load host key: /etc/ssh/ssh_host_ed25519_key

Then I set the folder permissions `/etc/.ssh/` like this:

    chmod 700 ~/.ssh
    chmod 644 ~/.ssh/authorized_keys
    chmod 644 ~/.ssh/known_hosts
    chmod 644 ~/.ssh/config
    chmod 600 ~/.ssh/id_rsa
    chmod 644 ~/.ssh/id_rsa.pub
    chmod 600 ~/.ssh/github_rsa
    chmod 644 ~/.ssh/github_rsa.pub
    chmod 600 ~/.ssh/mozilla_rsa
    chmod 644 ~/.ssh/mozilla_rsa.pub
    chmod 600 ~/.ssh_host_ed25519_key
    chmod 644 ~/.ssh_host_ed25519_key.pub

and reboot the server.


  [1]: https://documentation.online.net/en/dedicated-server/rescue/mount-lvm-partition