write a shell script to ssh to a remote machine and execute commands

There are multiple remote linux machines, and I need to write a shell script which will execute the same set of commands in each machine. (Including some sudo operations). How can this be done using shell scripting?

You can do this with ssh, for example:

#!/bin/bash
USERNAME=someUser
HOSTS="host1 host2 host3"
SCRIPT="pwd; ls"
for HOSTNAME in ${HOSTS} ; do
    ssh -l ${USERNAME} ${HOSTNAME} "${SCRIPT}"
done

When ssh'ing to the remote machine, how to handle when it prompts for RSA fingerprint authentication.

You can add the StrictHostKeyChecking=no option to ssh:

ssh -o StrictHostKeyChecking=no -l username hostname "pwd; ls"

This will disable the host key check and automatically add the host key to the list of known hosts. If you do not want to have the host added to the known hosts file, add the option -o UserKnownHostsFile=/dev/null.

Note that this disables certain security checks, for example protection against man-in-the-middle attack. It should therefore not be applied in a security sensitive environment.

Install sshpass using, apt-get install sshpass then edit the script and put your linux machines IPs, usernames and password in respective order. After that run that script. Thats it ! This script will install VLC in all systems.

#!/bin/bash
SCRIPT="cd Desktop; pwd;  echo -e 'PASSWORD' | sudo -S apt-get install vlc"
HOSTS=("192.168.1.121" "192.168.1.122" "192.168.1.123")
USERNAMES=("username1" "username2" "username3")
PASSWORDS=("password1" "password2" "password3")
for i in ${!HOSTS[*]} ; do
     echo ${HOSTS[i]}
     SCR=${SCRIPT/PASSWORD/${PASSWORDS[i]}}
     sshpass -p ${PASSWORDS[i]} ssh -l ${USERNAMES[i]} ${HOSTS[i]} "${SCR}"
done