How-to for crontab

[unutbu]

Perhaps try this:
Edit your crontab to include

DISPLAY=:0

at the top of the file.

This may or may not work, but if it does, here is the explanation:
cron runs commands in a stripped-down environment that doesn't include DISPLAY. Programs with GUIs often read DISPLAY to determine where to place its graphics.

[jaketrunk]

I must be doing something wrong. I've written a script to back up my system:


#!/bin/bash

tar cvpzf /var/lib/mythtv/videos/Backup/mythdown_backup.tgz --exclude=/proc --exclude=/lost+found --exclude=/mnt --exclude=/sys --exclude=/var/lib/mythtv/videos --exclude=/var/lib/mythtv/recordings /


And placed the script named backup in the /sbin directory. When I type (from the /sbin directory):

sudo backup

everything works great.

I've tried editing the crontab by typing:

sudo crontab -e

and then adding my script (30 19 * * * /sbin/backup).

The problem is the script will run, but will only backup a small portion of my system.

What am I doing wrong? Why does the script work from the command line, but not from cron?

Any help will be greatly appreciated.

[Gourgi]

I must be doing something wrong. I've written a script to back up my system:


#!/bin/bash

tar cvpzf /var/lib/mythtv/videos/Backup/mythdown_backup.tgz --exclude=/proc --exclude=/lost+found --exclude=/mnt --exclude=/sys --exclude=/var/lib/mythtv/videos --exclude=/var/lib/mythtv/recordings /


And placed the script named backup in the /sbin directory. When I type (from the /sbin directory):

sudo backup

everything works great.

I've tried editing the crontab by typing:

sudo crontab -e

and then adding my script (30 19 * * * /sbin/backup).

The problem is the script will run, but will only backup a small portion of my system.

What am I doing wrong? Why does the script work from the command line, but not from cron?

Any help will be greatly appreciated.

try using #!/bin/sh

[jaketrunk]

please see below

[jaketrunk]

try using #!/bin/sh

I made the changes, but still the same result. When run from the command line with sudo the script produces a full backup (~800 megs). When run from crontab, the file is only about 11 megs. Is there a way I can see what is causing the backup to end prematurely?

[unutbu]

Perhaps try changing

30 19 * * * /sbin/backup

to

* * * * * /sbin/backup 1>/tmp/backup.out 2>&1

Then wait a minute (for the cronjob to run) and then look in /tmp/backup.out.
It should contain all the output from stdout and stderr.
Look for any errors. That may give us a clue.

I think I recall one thread where the mere fact that stdout and stderr was directed somewhere was enough to make the cronjob succeed (whereas before it kept bailing out early). I haven't been able to reproduce this problem on my machine, but maybe you will find this true for you too.

[jaketrunk]

Perhaps try changing

30 19 * * * /sbin/backup

to

* * * * * /sbin/backup 1>/tmp/backup.out 2>&1

Then wait a minute (for the cronjob to run) and then look in /tmp/backup.out.
It should contain all the output from stdout and stderr.
Look for any errors. That may give us a clue.

I think I recall one thread where the mere fact that stdout and stderr was directed somewhere was enough to make the cronjob succeed (whereas before it kept bailing out early). I haven't been able to reproduce this problem on my machine, but maybe you will find this true for you too.

That did it! The script ran perfectly. Thank you so much for your help! Can you tell me in noob terms what "1>/tmp/backup.out 2>&1" does?

Thanks again!!

[unutbu]

Wonderful. I'm glad it worked for you jaketrunk.

Usually when you run a program from the terminal, the program has a notion of "stdout" and "stderr". When a program prints something to stdout, you see it on the screen.
stderr is similar to stdout except it is used for the program's error messages. Usually it is also printed in the terminal's window. Both stdout and stderr can be redirected to a single file, or to different files, or to /dev/null (a special file, where everthing sent there gets ignored.)

In contrast to programs run in the terminal, when you run cronjobs, stdout and stderr are not directed anywhere by default. (If you set up a mail transfer agent, however, you can get each cronjob's stdout and stderr to be sent to your mailbox...)

"1>/tmp/backup.out" tells /sbin/backup to send stdout to /tmp/backup.out.
"2>&1" tells /sbin/backup to send stderr to wherever stdout is pointed to.

The numbers 1 and 2 are file descriptors. By convention, file descriptor 1 is stdout, and file descriptor 2 is stderr.

[jaketrunk]

Unutbu, that makes sense. Thank you for the valuable info. I will keep in mind as a work on additional scripts.

[renaldy]

hello guys im having problem with my crontab, im still a newbie in this, i tried created a crontab that will make my com restart (just to learn how to use it,lol) and this is the line i wrote:

00 12 * * * /sbin/shutdown -r

however,it does not seem to work, i create this crontab in root account so i dont think it has got to do with privilege problem, someone please help me on this