Bonsoir,
Je reviens vers vous afin de vous demander conseil. Après le mode rescue, j'ai pu me reconnecter, j'ai remis l'ancien /etc/ssh/sshd_config mais en SSH restart il y a des erreurs. Voir ci-dessous. Je pense que je me dois de réinstaller openssh-server ainsi que le client. Comment puis-je faire ? Désinstaller et ensuite passer en mode rescue et réinstaller ? Merci pour vos suggestions. Bien cordialement.

service ssh restart
Job for ssh.service failed because the control process exited with error code.
See "systemctl status ssh.service" and "journalctl -xe" for details.
root@..........:~# systemctl status ssh.service
● ssh.service - OpenBSD Secure Shell server
   Loaded: loaded (/lib/systemd/system/ssh.service; enabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Fri 2020-04-24 12:05:44 CEST; 1min 52s ago
  Process: 25882 ExecStart=/usr/sbin/sshd -D $SSHD_OPTS (code=exited, status=0/SUCCESS)
  Process: 6876 ExecStartPre=/usr/sbin/sshd -t (code=exited, status=255)
 Main PID: 25882 (code=exited, status=0/SUCCESS)
    Tasks: 4 (limit: 4915)
   CGroup: /system.slice/ssh.service
           ├─ 6980 systemctl status ssh.service
           ├─ 6981 pager
           ├─19579 sshd: root@pts/2
           └─20098 -bash
ssh.service: Control process exited, code=exited status=255
systemd[1]: Failed to start OpenBSD Secure Shell server.
systemd[1]: ssh.service: Unit entered failed state.
systemd[1]: ssh.service: Failed with result 'exit-code'.
systemd[1]: ssh.service: Service hold-off time over, scheduling restart.
systemd[1]: Stopped OpenBSD Secure Shell server.
systemd[1]: ssh.service: Start request repeated too quickly.
systemd[1]: Failed to start OpenBSD Secure Shell server.
systemd[1]: ssh.service: Unit entered failed state.
systemd[1]: ssh.service: Failed with result 'exit-code

# Package generated configuration file
# See the sshd_config(5) manpage for details

# What ports, IPs and protocols we listen for
Port 22
# Use these options to restrict which interfaces/protocols sshd will bind to
#ListenAddress ::
#ListenAddress 0.0.0.0
Protocol 2
# HostKeys for protocol version 2
HostKey /etc/ssh/ssh_host_rsa_key
#HostKey /etc/ssh/ssh_host_dsa_key
#HostKey /etc/ssh/ssh_host_ecdsa_key
HostKey /etc/ssh/ssh_host_ed25519_key
#Privilege Separation is turned on for security
UsePrivilegeSeparation yes

# Lifetime and size of ephemeral version 1 server key
KeyRegenerationInterval 3600
ServerKeyBits 1024

# Logging
SyslogFacility AUTH
LogLevel INFO

# Authentication:
LoginGraceTime 120
#PermitRootLogin without-password
PermitRootLogin yes
StrictModes yes
RSAAuthentication yes
PubkeyAuthentication yes
#AuthorizedKeysFile     %h/.ssh/authorized_keys

# Don't read the user's ~/.rhosts and ~/.shosts files
IgnoreRhosts yes
# For this to work you will also need host keys in /etc/ssh_known_hosts
RhostsRSAAuthentication no
# similar for protocol version 2
HostbasedAuthentication no
# Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication
#IgnoreUserKnownHosts yes

# To enable empty passwords, change to yes (NOT RECOMMENDED)
PermitEmptyPasswords no

# Change to yes to enable challenge-response passwords (beware issues with
# some PAM modules and threads)
ChallengeResponseAuthentication no

# Change to no to disable tunnelled clear text passwords
#PasswordAuthentication yes

# Kerberos options
#KerberosAuthentication no

#KerberosGetAFSToken no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes

# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes

X11Forwarding yes
X11DisplayOffset 10
PrintMotd no
PrintLastLog yes
TCPKeepAlive yes
#UseLogin no

#MaxStartups 10:30:60
#Banner /etc/issue.net

# Allow client to pass locale environment variables
AcceptEnv LANG LC_*
Subsystem sftp /usr/lib/openssh/sftp-server


# Set this to 'yes' to enable PAM authentication, account processing,
# and session processing. If this is enabled, PAM authentication will
# be allowed through the ChallengeResponseAuthentication and
# PasswordAuthentication.  Depending on your PAM configuration,
# PAM authentication via ChallengeResponseAuthentication may bypass
# the setting of "PermitRootLogin without-password".
# If you just want the PAM account and session checks to run without
# PAM authentication, then enable this but set PasswordAuthentication
# and ChallengeResponseAuthentication to 'no'.
#UsePAM yes
Ciphers aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes128-ctr
MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sh$
KexAlgorithms diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sh$

Ok MattProd ! Le cryptage ! J'ai remplacé les dernières lignes par ceci. J'ai pu faire un reload SSH pour la première fois. Je vous tiens au courant tous pour la suite ! Merci à vous

Ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,chacha20-poly1305@openssh.com,aes256-gcm@openssh.com
HostKeyAlgorithms ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-rsa,ssh-dss,ssh-ed25519
KexAlgorithms curve25519-sha256@libssh.org,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,diffie-hellman-group16-sha512
MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,umac-128-etm@openssh.com

Bonjour à tous,
Voici quelques news ! Dès que je tente un changement au niveau de /etc/ssh/sshd_config toujours dans l’objectif de bloquer l’user dans son home en sftp. He bien je ne peux plus me connecter en SSH et en FTP ; comme au début de cet fil de discussion. J’ai suivi ce tuto
https://mondedie.fr/d/840-tuto-chrooter-les-utilisateurs-dans-leur-home-en-sftp

Merci pour vos réponses. Bien cordialement

Modification !!!!

Match user user1,user2,user3,user4
         ChrootDirectory /home/%u

Hello
Merci pour ton aide ! le problème est venu dès que j’ai créé deux nouveaux users (2) avec les droits d’accès dans le home directory. Depuis j’ai retiré le groupe ami et ses deux users.

su - chlotus
No directory, logging in with HOME=/
chlotus@GRE:/$

cat /etc/passwd
chlotus:x:1000:1000::/home/chlotus:/bin/bash

useradd alan --gid amis --groups amis -m --shell /bin/false

chown root /home/alan
chmod go-w /home/alan

mkdir /home/alan/notes
chown alan:amis /home/alan/notes
chmod ug+rwX /home/alan/notes

chlotus@GRE:/root$ ls -lisa /home/chlotus
ls: impossible d'accéder à '/home/chlotus': Aucun fichier ou dossier de ce type

Comme exprimé dans mon message précédent j'ai supprimé les deux users dont alan.