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2022-06-25 11:31:59 +02:00 · 2022-06-25 11:31:59 +02:00 · f6bf3003cd
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+---
+title: SSH
+---
+
+## Linux Server
+### Installation
+#### Debian
+`# apt install openssh-server`  
+
+#### Arch
+`# pacman -S openssh`  
+
+`# systemctl enable ssh`  
+
+### Configuration file
+`/etc/ssh/sshd_config`  
+
+Make sure to restart the sshd service after changes.  
+
+### Change port
+Uncomment `Port` and set any port number  
+
+### Root login
+`PermitRootLogin` setting  
+
+```
+yes -> Able to log in with password as root
+```
+
+### Password Authentication
+`PasswordAuthentication` setting  
+
+```
+yes -> Allow login with passwords
+no -> Only allow ssh keys
+```
+
+On OpenBSD also set `KbdInteractiveAuthentication` to `no`  
+
+## Windows Server
+Open PowerShell as administrator  
+`Add-WindowsCapability -Online -Name OpenSSH.Server`
+
+Start service  
+`Start-Service sshd`  
+
+Enable service  
+`Set-Service -Name sshd -StartupType 'Automatic'`  
+
+Check whether firewall rule exists  
+`Get-NetFirewallRule -Name *ssh*`  
+
+Create firewall rule for port 22  
+`New-NetFirewallRule -Name sshd -DisplayName 'OpenSSH Server (sshd)' -Enabled True -Direction Inbound -Protocol TCP -Action Allow -LocalPort 22`  
+
+## Linux Client
+### Configuration file
+`/etc/ssh/ssh_config`  
+
+### Connect to non-standard port
+`$ ssh -p (port) (user)@(ip)`  
+
+### X11 passthrough
+`$ ssh -X (user)@(ip)`  
+
+### ssh keys
+Create new key:  
+`$ ssh-keygen`  
+
+*Example* for ed25519 key:  
+`$ ssh-keygen -t ed25519`  
+
+The "-C" flag can be used to add comments in ssh key files.  
+
+Enable the ssh key:  
+`$ ssh-copy-id -i (public key file) (user)@(ip/domain)`  
+
+If you are copying the ssh key from a different client, use the "-f" flag  
+`$ ssh-copy-id -f -i (public key file) (user)@(ip/domain)`  
+
+## Windows Client
+Open PowerShell as administrator  
+`Add-WindowsCapability -Online -Name OpenSSH.Client`  
+
+## SSH Tunnel systemd Service
+SSH tunnels can be created as systemd services  
+
+*Example tunnel:*  
+`ssh -NTfL 8080:webserver:80 user@remotehost`  
+
+### Tunnel settings
+Save the file under `/etc/systemd/system/(application/tunnel name)`  
+```
+PATH_TO_KEY=(ssh key path)
+LOCAL_PORT=8080
+REMOTE_ADDR=webserver
+REMOTE_PORT=80
+REMOTE_USER=user
+REMOTE_HOST=remotehost
+```
+
+### Tunnel service
+This service can be used with multiple different "tunnel settings" files. Similar to how the wg-quick service works with different wireguard configs.  
+Save this file under `/etc/systemd/system/local-tunnel@.service`  
+```
+[Unit]
+Description=Setup a local tunnel to %I
+After=network.target
+
+[Service]
+EnvironmentFile=/etc/default/local-tunnel@%i
+ExecStart=/usr/bin/ssh -i ${PATH_TO_KEY} -o ServerAliveInterval=60 -o ExitOnForwardFailure=yes -nNT -L ${LOCAL_PORT}:${REMOTE_ADDR}:${REMOTE_PORT} ${REMOTE_USER}@${REMOTE_HOST}
+RestartSec=15
+Restart=always
+KillMode=mixed
+
+[Install]
+WantedBy=multi-user.target
+```
+
+Finally, the tunnel can be enabled  
+`# systemctl daemon-reload`  
+`# systemctl enable --now local-tunnel@(application/tunnel name)`  
+
+## References
+- [Windows OpenSSH Installation](https://docs.microsoft.com/en-us/windows-server/administration/openssh/openssh_install_firstuse)  
+- [SSH Tunnel as systemd service](https://ivanmorenoj.medium.com/ssh-tunnel-as-systemd-service-3c53bd157ac1)