Creating cron entry on server using ssh login within shell script

Question

I need to upload a file (bash script) to a remote sever. I use the scp command. After the file has been copied to the remote server I want to create a cron entry in the crontab file on the remote server. However, the file upload and writing the cron entry need to occur within a bash shell script so that I only need to execute the script on my local machine and the script is copied to the remote host and the cron entry is written to the crontab.

Is there a way that I can use an ssh command, within the script, that logs me into the remote server, opens the crontab file and writes the cron entry.

Any help is very welcome

glenn jackman · Accepted Answer · 2011-02-18 02:48:06Z

8

I would:

extract the user's crontab with crontab -l > somefile
modify that file with the desired job
import the new crontab with crontab somefile

answered Feb 18, 2011 at 2:48

glenn jackman

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MobiusTrip · Accepted Answer · 2013-09-16 08:28:52Z

2

I just did something like this where I needed to create a multiline line crontab on a remote machine. By far the simplest solution was to pipe the content to the remote crontab command through ssh like this:

echo "$CRON_CONTENTS" | ssh username@server crontab

answered Sep 16, 2013 at 8:28

MobiusTrip

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Mat Schaffer · Accepted Answer · 2011-02-17 22:20:59Z

0

mailo seemed almost right, but the command would be the second argument to the ssh command, like this:

ssh username@server 'echo "* * * * * /path/to/script/" >> /etc/crontab'

Or if your system doesn't automatically load /etc/crontab you should be able to pipe to the crontab command like this:

ssh username@server 'echo "* * * * * myscript" | /usr/bin/crontab'

answered Feb 17, 2011 at 22:20

Mat Schaffer

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tripleee · Accepted Answer · 2012-05-26 06:56:19Z

Say you want to copy $local to $remote on $host and add an hourly job there to run at 14 past every hour, using a single SSH session;

ssh "$host" "cat >'$remote' && 
    chmod +x '$remote' && 
    ( crontab -l; 
      echo '14 * * * * $remote' ) | crontab" <"$local"

This could obviously be much more robust with proper error checking etc, but hopefully it should at least get you started.

The two keys here are that the ssh command accepts an arbitrarily complex shell script as the remote command, and gets its standard input from the local host.

(With double quotes around the script, all variables will be interpolated on the local host; so the command executed on the remote host will be something like cat >'/path/to/remote' && chmod +x '/path/to/remote' && ... With the single quotes, you could have whitespace in the file name, but I didn't put them in the crontab entry because it's so weird. If you need single quotes there as well, I believe it should work.)

mailo · Accepted Answer · 2011-02-17 20:42:09Z

-1

You meant something like

ssh [email protected] && echo "* * * * * /path/to/script/" >> /etc/crontab

?

answered Feb 17, 2011 at 20:42

mailo

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1 Comment

kmarsh Over a year ago

The echo and redirection to the locally created /etc/crontab only occurs after the successful exit of an SSH login. Not really what the OP asked for.

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