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

Question

I have two questions:

1. 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.

Answer 1

This worked for me. I made a function. Put this in your shell script:

sshcmd(){
    ssh $1@$2 $3
}

sshcmd USER HOST COMMAND

If you have multiple machines that you want to do the same command on you would repeat that line with a semi colon. For example, if you have two machines you would do this:

sshcmd USER HOST COMMAND ; sshcmd USER HOST COMMAND

Replace USER with the user of the computer. Replace HOST with the name of the computer. Replace COMMAND with the command you want to do on the computer.

Hope this helps!

Answer 2

If you are able to write Perl code, then you should consider using Net::OpenSSH::Parallel.

You would be able to describe the actions that have to be run in every host in a declarative manner and the module will take care of all the scary details. Running commands through sudo is also supported.

Answer 3

There is are multiple ways to execute the commands or script in the multiple remote Linux machines. One simple & easiest way is via pssh (parallel ssh program)

pssh: is a program for executing ssh in parallel on a number of hosts. It provides features such as sending input to all of the processes, passing a password to ssh, saving the output to files, and timing out.

Example & Usage:

Connect to host1 and host2, and print "hello, world" from each:

 pssh -i -H "host1 host2" echo "hello, world"

Run commands via a script on multiple servers:

pssh -h hosts.txt -P -I<./commands.sh

Usage & run a command without checking or saving host keys:

pssh -h hostname_ip.txt -x '-q -o StrictHostKeyChecking=no -o PreferredAuthentications=publickey -o PubkeyAuthentication=yes' -i  'uptime; hostname -f'

If the file hosts.txt has a large number of entries, say 100, then the parallelism option may also be set to 100 to ensure that the commands are run concurrently:

pssh -i -h hosts.txt -p 100 -t 0 sleep 10000

Options:
-I: Read input and sends to each ssh process.
-P: Tells pssh to display output as it arrives.
-h: Reads the host's file.
-H : [user@]host[:port] for single-host.
-i: Display standard output and standard error as each host completes
-x args: Passes extra SSH command-line arguments
-o option: Can be used to give options in the format used in the configuration file.(/etc/ssh/ssh_config) (~/.ssh/config)
-p parallelism: Use the given number as the maximum number of concurrent connections
-q Quiet mode: Causes most warning and diagnostic messages to be suppressed.
-t: Make connections time out after the given number of seconds. 0 means pssh will not timeout any connections

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

Disable the StrictHostKeyChecking to handle the RSA authentication prompt.
-o StrictHostKeyChecking=no

Source: man pssh