SSH tricks

Basics

Run remote command

ssh zk-testing -t 'tail -1000 ~/.walletwasabi/backend/Logs | grep whatever'

To run complex remote shell cmds over ssh, without escaping quotes

ssh host -l user $(<cmd.txt)

Much simpler method. More portable version: ssh host -l user “cat cmd.txt”

Download a file

scp zk-testing:./.bitcoin/mempool.dat ./mempool.dat

Create a persistent connection to a machine

Create a persistent ssh connection so all future sessions will reuse it.

-f Requests ssh to go to background just before command execution.
-M Places the ssh client into ``master’’ mode for connection sharing.

ssh -MNf zk-testing

Tunneling

Port forward testnet RPC

-L local_socket:host:hostport
-N Do not execute a remote command. This is useful for just forwarding ports.

ssh -N -L 18332:localhost:18332 zk-testing

Port forward testnet P2P

ssh -N -L 8332:localhost:8332 zk-testing

Edit remote files (Vim)

First, create a persistent connection to the server.

ssh -MNf zk-testing

Note: you can use -v to see what is going on. Also, his command line can be run in background finishing the command line wih & but it will not ask you the password :(

Edit remote files

Using relative paths

vim scp://zk-testing/report.sh

It is also okay to open a direcory

vim scp://zk-testing/

Using absolute paths

vim scp://zk-testing//home/user/report.sh

Copy ssh key to the server.

ssh-copy-id zk-testing

Copy your ssh public key to a server from a machine that doesn’t have ssh-copy-id

cat ~/.ssh/id_rsa.pub | ssh user@machine “mkdir ~/.ssh; cat >> ~/.ssh/authorized_keys”

Transfer ssh public key to another machine in one step

ssh-keygen; ssh-copy-id zk-testing; ssh zk-testing

This command sequence allows simple setup of (gasp!) password-less SSH logins. Be careful, as if you already have an SSH keypair in your ~/.ssh directory on the local machine, there is a possibility ssh-keygen may overwrite them. ssh-copy-id copies the public key to the remote host and appends it to the remote account’s ~/.ssh/authorized_keys file. When trying ssh, if you used no passphrase for your key, the remote shell appears soon after invoking ssh user@host.

To generate the keys use the command ssh-keygen

Copy directory from testing to production

ssh zk-testing "cd /somedir/tocopy/ && tar -cf – ." | ssh zk-producion "cd /samedir/tocopyto/ && tar -xf -"

Good if only you have access to host1 and host2, but they have no access to your host (so ncat won’t work) and they have no direct access to each other.

Mount filesystem through ssh

sshfs name@server:/path/to/folder /path/to/mount/point

Will allow you to mount a folder security over a network.

SSH connection through host in the middle

ssh -t reachable_host ssh unreachable_host

Unreachable_host is unavailable from local network, but it’s available from reachable_host’s network. This command creates a connection to unreachable_host through “hidden” connection to reachable_host.