autossh:tldr:f3a46

This command is using the autossh tool to establish a secure tunnel between a local machine and a remote server.

Here is the breakdown of each option:

• -f: This option runs autossh in the background.
• -M 0: This option disables the monitoring port. Normally, autossh uses a port to monitor the connection, but setting it to 0 disables this feature.
• -N: This option tells autossh not to execute any remote commands. It is used when you only need to establish the connection without running any specific commands on the remote server.
• -o "ServerAliveInterval 10": This sets the interval (in seconds) at which autossh sends keep-alive messages to the server to check if the connection is still active.
• -o "ServerAliveCountMax 3": This sets the maximum number of keep-alive messages that can be sent without receiving any response before considering the connection as inactive.
• -o ExitOnForwardFailure=yes: This option tells autossh to terminate the connection if it fails to set up the specified port forwarding.
• -L ${local_port}:localhost:${remote_port}: This sets up local port forwarding. Any traffic sent to localhost:${local_port} on the local machine will be forwarded to localhost:${remote_port} on the remote server.
• ${user}@${host}: Specifies the user and the hostname (or IP address) of the remote server to connect to.

In summary, this command establishes a persistent SSH tunnel and forwards local traffic from ${local_port} to the remote ${remote_port} on the ${host} machine, using the SSH credentials for ${user}. The ServerAliveInterval and ServerAliveCountMax options ensure the connection stays active, and ExitOnForwardFailure terminates the connection if the port forwarding fails.