Wait for a remote script to finish before executing another

vikas027 · 08-02-2012, 05:58 PM

Dear All,

I am sitting on box1 and want to zip (tar.bz2) multiple directories on box2 and then fire another command to scp the tar balls from box2 to box1.

I have set up ssh keys but still using 'perl expect' as I am using sudo commands (which asks for an extra password).

My problem is that scp starts before the first script (to create tar balls) finishes

This is a piece of my code:

Code:

 
echo "ssh -t $host \"sudo bash /tmp/tar_template\"" > cmd 
pass
 
echo "scp -r $host:$RSERVER_WORKING_DIR/$dt1 $NFS_MOUNT_POINT/$host/" > cmd
pass

Here, /tmp/tar_template is the script which is creating tar balls and pass is the function which is providing the password.

Any ways to execute the second command only after the first finishes. I can put sleeps but that will not be appropriate since time to zip (tar.bz2) the directory varies.

Another way would be to put a indefinite loop to check a lock file on the remote server and run only when it is deleted by the first command/script, BUT I dont want that since it will unnecessary have multiple login entries.

I tried some combination of wait command, but that did not worked for me.

Please help. Thanks in advance.

pingu · 08-04-2012, 04:05 AM

Put && after the first script.
Script 2 will then be executed only if script 1 finishes without failure.

vikas027 · 08-04-2012, 01:21 PM

Quote:

Originally Posted by pingu

Put && after the first script.
Script 2 will then be executed only if script 1 finishes without failure.

Hi Pingu,

Putting && will not work since the commands (or scripts) will run on another server and on the same server.

To elaborate, suppose I create two functions abc1 and abc2

Code:

abc1 ()
{
echo "ssh -t server2 \"sudo bash /tmp/tar_template\"" > cmd 
pass
}
 
abc2 ()
{
echo "scp -r server2:$RSERVER_WORKING_DIR/$dt1 $NFS_MOUNT_POINT/$host/" > cmd
pass
}

Now, if I run abc1 && abc2 on server1, abc2 will be executed immediately after abc1 since it is running on a different server (server2) and server1 has no way to know that the command/script has been completed or not on server1.

I hope I am clear

pingu · 08-04-2012, 02:58 PM

Ah, sorry of course you're right.

So, on Box1 you need a way to run script-2 only when script-1 on Box2 is finished.
I can see 2 ways to do this. (Ok, it's ten-o-clock in the evening, I've worked hard and had 2 glasses of wine. I still know what I'm doing but please keep that in mind, I might miss some details.)

1) Scp the other way, meaning you put everything in one script on remote host.
You already have keys set up, so all you need do then is remove password prompting from box2 -> box1.

2) A bit more complicated, but also more elegant if you ask me:
a) Run script-1 on Box1, the one that starts a tarball-creating on Box2. Put the tarball in a dedicated directory (from now on called "DDIR") on Box2.
b) On Box2, use inotifywait to watch DDIR with "close write".
Make a script on Box2 that uses inotifywait so that when a file is written to DDIR a file is created with name "tarball_complete".
c) On Box1, create a script that watches for this file on Box2, and downloads the tarball when the "tarball-complete"-file exists.
Easiest is to make it a cron-job, or you could have a loop in a small script to check for that file.
Of course, you'll have to provide your password every time the script is checking. If I were you I'd run those scripts under a special, very restricted user-account and use only ssh-keys.

vikas027 · 08-07-2012, 01:48 AM

Quote:

Originally Posted by pingu

Ah, sorry of course you're right.

So, on Box1 you need a way to run script-2 only when script-1 on Box2 is finished.
I can see 2 ways to do this. (Ok, it's ten-o-clock in the evening, I've worked hard and had 2 glasses of wine. I still know what I'm doing but please keep that in mind, I might miss some details.)

1) Scp the other way, meaning you put everything in one script on remote host.
You already have keys set up, so all you need do then is remove password prompting from box2 -> box1.

2) A bit more complicated, but also more elegant if you ask me:
a) Run script-1 on Box1, the one that starts a tarball-creating on Box2. Put the tarball in a dedicated directory (from now on called "DDIR") on Box2.
b) On Box2, use inotifywait to watch DDIR with "close write".
Make a script on Box2 that uses inotifywait so that when a file is written to DDIR a file is created with name "tarball_complete".
c) On Box1, create a script that watches for this file on Box2, and downloads the tarball when the "tarball-complete"-file exists.
Easiest is to make it a cron-job, or you could have a loop in a small script to check for that file.
Of course, you'll have to provide your password every time the script is checking. If I were you I'd run those scripts under a special, very restricted user-account and use only ssh-keys.

Many thanks for your time and suggestions Pingu.

I am not authorized to do much changes on the servers

, I have to manage from current setup only.

I have managed it to by creating a lock file in the start of the script-1 and delete it when it finished. I am checking the lock file at a particular interval and this solved my issue. But frankly, I am not happy with it.