Multiple commands during an SSH inside an SSH session

You can always define in your jumpbox Multiplexing in OpenSSH

Multiplexing is the ability to send more than one signal over a single line or connection. With multiplexing, OpenSSH can re-use an existing TCP connection for multiple concurrent SSH sessions rather than creating a new one each time.

An advantage with SSH multiplexing is that the overhead of creating new TCP connections is eliminated. The overall number of connections that a machine may accept is a finite resource and the limit is more noticeable on some machines than on others, and varies greatly depending on both load and usage. There is also significant delay when opening a new connection. Activities that repeatedly open new connections can be significantly sped up using multiplexing.

For that do in /etc/ssh/ssh_config:

ControlMaster auto
ControlPath ~/.ssh/controlmasters/ssh_mux_%h_%p_%r
ControlPersist 30m

In this way, any consecutive connections made to the same server in the following 30 minutes will be done reusing the previous ssh connection.

You can also define it for a machine or group of machines. Taken from the link provided.

Host machine1
    HostName machine1.example.org
    ControlPath ~/.ssh/controlmasters/%r@%h:%p
    ControlMaster auto
    ControlPersist 10m

You can put all your commands into a separate script on your "master" server.

Master Script

#!/bin/bash
rm -rf "Input Output Partition"
mkdir -p "EC2_WORKSPACE/$project Input Output Partition"

Then in your ssh script call it like this: SSH Script

username="ubuntu"
masterHostname="myMaster"
while read line
do
ssh -n $username@$masterHostname "ssh -t -t $username@$line < /path/to/masterscript.sh"
ssh -n $username@$masterHostname "ssh -t -t $username@$line "rsync --delete -avzh /EC2_NFS/$project/* EC2_WORKSPACE/$project""
done < slaves.txt 

OR if all files must be on the initial machine you could do something like this:

script1

script2="/path/to/script2"
username="ubuntu"
while read line; do
cat $script2 | ssh -t -t $username@line
done < slaves.txt

script2

#!/bin/bash
rm -rf "Input Output Partition"
mkdir -p "EC2_WORKSPACE/$project Input Output Partition"
rsync --delete -avzh "/EC2_NFS/$project/* EC2_WORKSPACE/$project"

ssh script

script1="/path/to/script1"
username="ubuntu"
masterHostname="myMaster"
cat $script1 | ssh -n $username@$masterHostname

Some time ago, I had occasion to use control sockets like the other answers recommend (this answer is essentially a combination of using control sockets like this answer and scripts like this answer).

The use case was a hack: The authorized_keys of the target user was overwritten periodically by a scheduled task and I wanted to quickly test things without going through red-tape needed to add something to that file. So I'd setup a while loop which added the key to that file as needed, run my test, and the cancel the loop. However, there would be a small window where the scheduled task would overwrite the file and my loop would still be sleeping. So, setting up a control socket at the start would let my script SSH later without problems:

#! /bin/bash -xe
. "${CONFIG_DIR}/scripts/setup-ssh.sh"

# Build and test
export TEST_LABEL="${_started_by}-${BUILD_TAG%-BUILD*}"
#...
xargs --arg-file test-list \
    --no-run-if-empty \
    --process-slot-var=NUM \
    --max-procs=${#SERVERS[@]} \
    --max-args="${BATCH_SIZE:-20}" \
    "${CONFIG_DIR}/scripts/run-test.sh"

Where setup-ssh.sh is:

export SSH_CONFIG="${CONFIG_DIR}/scripts/.ssh-config"
mapfile -t SERVERS < "${CONFIG_DIR}/scripts/hosts"

for SERVER in "${SERVERS[@]}"
do
    while ! ssh -F "${SSH_CONFIG}" "${SERVER}" -fnN; do sleep 1; done
    scp -F "${SSH_CONFIG}" "${CONFIG_DIR}/scripts/ssh-script.sh" "${SERVER}":"${TEST_LABEL}.sh"
done

And .ssh-config:

Host test-*
  User test
  StrictHostKeyChecking no
  ControlMaster auto
  ControlPath /tmp/ssh-%h-%p-%r

And run-test.sh:

mapfile -t TEST_SERVERS < "${CONFIG_DIR}/scripts/hosts"
ssh -F "${SSH_CONFIG}" "${TEST_SERVERS[$NUM]}" "./${TEST_LABEL}.sh"

The sequence goes like this:

• The main script (shown first) sources setup-ssh.sh.
• setup-ssh.sh busy-loops the servers until all of them have a control socket setup. The hosts file simply lists the server hostnames one per line.
• Since the configuration specifying the control socket is only in ${CONFIG_DIR}/scripts/.ssh-config, unless I specify that file using -F, SSH connections won't use it. So this allows me to use the control socket only where I need them using the F option.
• The setup script also copies the test execution script to the servers. The execution script itself contains a bunch of commands, and because I copied the execution script, I don't have to worry about an additional layer of quoting for SSH (and the additional cognitive overhead for figuring out what gets expanded when).
• Then the main script uses xargs to distribute the workload over the servers, by starting new jobs as soon as running ones end.