Keep persistent SSH session using autossh and cron
Keep persistent SSH session using autossh and cron
Background Knowledge
SSH Tunneling
- Local Port Forwarding: used to forward a port from the client machine to the server machine.
- Remote Port Forwarding:
Local Port Forwarding
ssh -L [bind_addr:]port:target_addr:target_port user@server
- bind_addr
- port
- target_addr
- target_port
- user
- server
Remote Port Forwarding
ssh -R [bind_addr:]port:target_addr:target_port user@server
- bind_addr
- port
- target_addr
- target_port
- user
- server
Please see http://dirk-loss.de/ssh-port-forwarding.pdf
Prerequisites
- autossh
sudo apt-get install autossh
Server Side
Add User for SSH tunneling
sudo adduser --system --shell /bin/false --gecos "Auto SSH" --disabled-password --home=/home/autossh autossh
Generate SSH key
sudo -u autossh ssh-keygen -t rsa -b 4096 -f ~/.ssh/autossh
Copy public key to ~/.ssh/authorized_keys
sudo -u autossh cp ~/.ssh/autossh.pub ~/.ssh/authorized_keys
Append Follwing Configuration to /etc/ssh/sshd_config
if did you want Local Port Forwarding please set GatewayPorts to yes.
Match User autossh
...
GatewayPorts no
...
Restart SSH daemon
sudo systemctl restart ssh
Client Side
Copy SSH private key to client host
scp 1.2.3.4/.ssh/autossh ~/.ssh/autossh
Install autossh
sudo apt install autossh
Add SSH Client Configurations
Append following config to ~/.ssh/config
Replace 1.2.3.4 to real IP or hostname
for Local Forwarding
only allowed if GatewayPort=yes (default: no) in server configuration.
LocalForward 2222 localhost:22
for Remote Forwarding
RemoteForward** 2222 localhost:22
Test SSH connection
autossh -M 0 -f -N autossh
Verify SSH Connection
Check listen port in your system.
for Local Port Forward (in Server)
netstat -lnt
for Remote Port Forward (in Client)
netstat -lnt
ps aux |grep autossh
Copy autossh-bot to ~/bin
mkdir -p ~/bin
cp ./bin/auto-ssh-bot ~/bin
Register cron job
crontab -e
Schedule cron job to every 5 minutes
0/5 * * * * ~/bin/auto-ssh-bot
