I'm wondering if I already have an established SSH tunnel and I want to minimize re-authenticating with an ssh server for each task, is there a way to use an existing tunnel to pull a file from the SSH server using SCP on the local machine without re-authenticating?
I'm trying to avoid using ssh keys, I'd just like to minimize the amount of times a password needs to be entered for a bash script.
ssh -t user#build_server "*creates a build file...*"
Once that command is completed there is a file that exists on build_server. So if the above tunnel was still open, is there way to use that tunnel from my LOCAL machine to run SCP to and bring the file to the local machines desktop?
Yes, session sharing is possible: man ssh_config and search for ControlMaster and/or check here and here. Is this what you are looking for?
Related
Essentially what I want to do is run a Bash script I created that switches WiFi SSIDs before starting the SSH connection, and after the SSH connection closes.
I have added this to ~/.ssh/config by setting ProxyCommand to ./run-script; ssh %h:%p but by doing this, I feel like it would ignore any parameters I passed when I run the ssh command. Also, I have no idea how to get the script to run again when the SSH connection closes.
For OpenSSH you can specify a LocalCommand in your ssh config (~/.ssh/config).
But for that to work you also need the system-wide option (in /etc/ssh/ssh_config) PermitLocalCommand to yes. (By default it is set to no.)
It gets executed on the local machine after authenticating but before the remote shell is started.
There appears to be no (easy) way of executing something after the connection has been closed, though.
Assuming that it is not possible to implement a wrapper to 'ssh' (using alias, or some other method), it is possible to implement the following in the proxyCommand.
Important to note that there is no protection against multiple invocation of 'ssh' - possible that during a specific invocation that WIFI is already connected. Also, it is possible that when a specific ssh is terminated, the WIFI has to stay active because of other pending conditions.
Possible implementation of the proxy script is
ProxyCommand /path/to/run-script %h %p
#! /bin/sh
pre-command # connect to WIFI
nc -N "$1" "$2" # Tunnel, '%h' and '%p' are passed in
post-command # Disconnect WIFI
You do not want to use simple ssh in the proxy script, as this will translate into another call to the 'run-script'. Also note that all options provided to the original ssh will be handled by the initial 'ssh' session that will be leveraging the proxy 'nc' tunnel.
I am working on a script which will be used to transfer a file (using rsync) from a remote location and then perform some basic operations on the retrieved content.
When I initially connect to the remote location (not running an rsync daemon, I'm just using rsync to retrieve the files) I am placed in a non-standard shell. In order to enter the bash shell I need to enter "run util bash". Is there a way to execute "run util bash" before rsync begins to transfer the files over?
I am open to other suggestions if there is a way to do this using scp/ftp instead of rsync.
One way is to exectue rsync from the server, instead of from the client. An ssh reverse tunnel allows us to temporarily access the local machine from the remote server.
Assume the local machine has an ssh server on port 22
Shh into the remote host while specifying a reverse tunnel that maps a port in the remote machine (in this example let us use 2222) to port 22 in our local machine
Execute your rsync command, replacing any reference to your local machine with the reverse ssh tunnel address: my-local-user#localhost
Add a port option to rsync's ssh to have it use the 2222 port.
The command:
ssh -R 2222:localhost:22 remoteuser#remotemachine << EOF
# we are on the remote server.
# we can ssh back into the box running the ssh client via ${REMOTE_PORT}
run utils bash
rsync -e "ssh -p 2222" --args /path/to/remote/source remoteuser#localhost:/path/to/local/machine/dest
EOF
Reference to pass complicated commands to ssh:
What is the cleanest way to ssh and run multiple commands in Bash?
You can achieve it using --rsync-path also. E.g rsync --rsync-path="run util bash && rsync" -e "ssh -T -c aes128-ctr -o Compression=no -x" ./tmp root#example.com:~
--rsync-path is normally used to specify what program is to be run on the remote machine to start-up rsync. Often used when rsync is not in the default remote-shell’s path (e.g. –rsync-path=/usr/local/bin/rsync). Note that PROGRAM is run with the help of a shell, so it can be any program, script, or command sequence you’d care to run, so long as it does not corrupt the standard-in & standard-out that rsync is using to communicate.
For more details refer
I am very new in shell scripting , i want to download some files from linux remote server ,so how can i proceed for that.That remote server is ssh based .
first of all, ftp service is better choice to get files from remote server.
If only sshd service is available, then you may use ssh based command sftp or scp.
However, using sftp or scp commands will invoke an interactive password prompt, which is a problem in shell script --> You have to ask for help to expect command. see Automate scp file transfer using a shell script .
Besides expect, you may also set up trust relationship between two servers, then you may use scp without password. See http://www.linuxproblem.org/art_9.html
The scenario is like:
SERVER_A="servera.com"
SERVER_A_UNAME="usera"
SERVER_B="serverb.com"
SERVER_B_UNAME="userb"
I want to write a shell script which will fist connect to server A, and then only it would be connected to server B. Like:
#!/bin/sh
ssh $SERVER_A_UNAME#$SERVER_A ...and then
ssh $SERVER_B_UNAME#$SERVER_B
But I am not able to do it. It does connect to server A only. How can I achieve it?
You may be able to find some help with this previous question:
How to use bash/expect to check if an SSH login works
Depending on your situation you might also to execute an remote ssh command and wait for positive feedback.
See:
How to use SSH to run a shell script on a remote machine?
you should have a look at ssh ProxyCommands that lets you do indirect connects automatically. basically you put the following in you .ssh/config
Host gateway1
# nichts
Host gateway2
ProxyCommand ssh -q gateway1 nc -q0 gateway2 22
Host targethost
ProxyCommand ssh -q gateway2 nc -q0 targethost 22
and then you can run ssh targethost successfully even if targethost is not reachable directly. you can read more about this e.g. here http://sshmenu.sourceforge.net/articles/transparent-mulithop.html
I have to run a shell script which is on a remote machine from the script on my local machine.
I thought of using ssh in my script but it would prompt for password which does not help as I will need to make this script run as a cronjob.
Could anyone just guide me like what would be ideal to use rather than using ssh to connect to the remote machine and run the script present there.
First of all you can set up passwordless ssh connections using private keys (that's what I should do).
If that's not an option, well there is expect, and here's an old but working tutorial.