如何通过shell脚本从machineX在machineA上执行命令？

Question

I have an application server running on Ubuntu 12.04 which I am starting and stopping by below commands -

For stopping the app server

david@machineA:/opt/kml$ /opt/kml/bin/kml_start_stop.sh stop

For starting the app server

david@machineA:/opt/kml$ /opt/kml/bin/kml_start_stop.sh start

Now I am trying to write a shell script which will stop and start my application server by using the above command but this shell script I will be running from machineX . And from machineX we can login passwordless without typing any password for user david to machineA

For example - From machineX I can do ssh david@machineA without typing my password.

Below is what I have started. Does everything looks right?

#!/bin/bash

ssh david@machineA

/opt/kml/bin/kml_start_stop.sh stop
sleep 10s
/opt/kml/bin/kml_start_stop.sh start

Answer 1

You could use a here document to execute remotely some script:

ssh david@machineA << EOJ
  /opt/kml/bin/kml_start_stop.sh stop
  sleep 10
  /opt/kml/bin/kml_start_stop.sh start
EOJ

in your case, you could also execute several ssh commands and sleep locally:

ssh david@machineA /opt/kml/bin/kml_start_stop.sh stop
sleep 10
ssh david@machineA /opt/kml/bin/kml_start_stop.sh start

BTW, I recommend learning more about shell scripting. You could read Advanced Bash Scripting Guide (with a critical eye, it does have imperfections) and the documentation of GNU bash . In particular, to do that on several machines, you might use some bash for loop.

Answer 2

No, you cannot do that because ssh will login and wait for commands, whereas you want to feed the commands to the very same ssh. The script should look more like this:

#!/bin/bash
while read host rest; do
  ssh david@$host <<EOF &
  /opt/kml/bin/kml_start_stop.sh stop
  sleep 10s
  /opt/kml/bin/kml_start_stop.sh start
  EOF
done < hostlist.txt
wait

That uses a Bash feature called a "here document" which feeds the text to the stdin of the ssh process.

Edit: I added a small trick: I background each of the ssh jobs as they are started, because each one will take some time to complete (at least 10 seconds due to the sleep). Then at the end I do wait to wait for all of them to complete. This way, the entire script can run in 10 seconds plus the overhead time, regardless of how many servers there are.

Answer 3

This script would execute the commands on the remote terminal.

#!/bin/bash

ssh david@machineA '/opt/kml/bin/kml_start_stop.sh stop && sleep 10s && /opt/kml/bin/kml_start_stop.sh start'

In case if you have used the below script then, a separate ssh session shell would be spawned to connect to the remote machine and the below commands would be run on the local machine shell instead on the remote

#!/bin/bash

ssh david@machineA 
/opt/kml/bin/kml_start_stop.sh stop
sleep 10s
/opt/kml/bin/kml_start_stop.sh start