CODEWITHSUNDEEP
ubuntucron
Sasikiran Vaddi
Sasikiran Vaddi

Reputation: 2319

Cron jobs output on console

I have written a shell script (myscript.sh):

#!/bin/sh
ls
pwd

I want to schedule this job for every minute and it should display on the console. In order to do that I have done crontab -e:

*/1 * * * * /root/myscript.sh

Here, it's display the output in the file /var/mail/root rather than printing on the console.

What changes I have to make inorder to print the output on console?

Upvotes: 4

Views: 27205

Answers (3)

denshigomi
denshigomi

Reputation: 151

One option would be to use "wall" in your script to display a message to all terminals. E.G.

wall -n Display this message to all terminals.

Upvotes: 0

GeorgiosDoumas
GeorgiosDoumas

Reputation: 81

I tried to achieve the output of a cron job to a gnome terminal , and managed it by this

*/1 * * * * /root/myscript.sh > /dev/pts/0

I suppose if you do not have a GUI and you only have CLI you might use

*/1 * * * * /root/myscript.sh > /dev/tty1

to achieve the output of a crontab job to be redirected to your console. But first be sure to find the name of your terminal. if it is /dev/tty1 or something else. I am not sure how this can be done for all cases, probably with something like

env | grep -i tty

Upvotes: 5

Dunes
Dunes

Reputation: 40788

The easiest way I can think of is to log the output to disk and have a console window constantly checking to see if the logfile has been altered and printing the changes.

crontab:

*/1 * * * * /root/myscript.sh | tee -a /path/to/logfile.log

in console:

tail -F /path/to/logfile.log

The problem with this is that you will get an ever growing log file which will need to be periodically deleted.

To avoid this you would have to do something more complicated whereby you identify the console pid that you wish to write to and store this in a predefined place.

console script:

#!/usr/bin/env bash

# register.sh script    
# prints parent pid to special file

echo $PPID > /path/to/predfined_location.txt

wrapper script for crontab

#!/usr/bin/env bash

cmd=$1
remote_pid_location=$2

# Read the contents of the file into $remote_pid.
# Hopefully the contents will be the pid of the process that wants the output 
# of the command to be run.
read remote_pid < $remote_pid_location

# if the process still exists and has an open stdin file descriptor
if stat /proc/$remote_pid/fd/0 &>/dev/null
then
    # then run the command echoing it's output to stdout and to the
    # stdin of the remote process
    $cmd | tee /proc/$remote_pid/fd/0 
else
    # otherwise just run the command as normal
    $cmd
fi

crontab usage:

*/1 * * * * /root/wrapper_script.sh /root/myscript.sh /path/to/predefined_location.txt

Now all you have to do is run register.sh in the console you want the program to print to.

Upvotes: 5

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