Cron jobs on Ubuntu EC2 Instance

Question

Help please, I can't seem to get cron jobs to run. I've always done crontab -e to schedule jobs but it doesn't seem to work on my EC2 instance running Ubuntu. I also tried sudo vi /etc/crontab and that doens't work either. I tried to schedule the job /usr/bin/echo "test" > /home/ubuntu/crontest.txt in /etc/crontab as root and as ubuntu but I never see the test file written. I googled and there are a few StackOverflow posts from people who had trouble with cron. But it seems many of them are able to get it to work after editing the /etc/crontab file. Can someone help me figure out why I can't get my jobs to run in cron?

Any help or pointers would be greatly appreciated. Thank you.

Answer

Hi, Good Question

I was curious about this, so I have setup a `Ubuntu 20.04` and I was able to use crontab.

crontab's are generally setup per user. when you login, you would be logging in as a ec2-user.
Let's assume that you have logged in as `ec2-user`, so you could check if there is a crontab by running `crontab -l`. If there is no crontab then you would see something like the following
```
crontab -l
no crontab for ubuntu
```

to add a crontab, you could use `crontab -e`, use the editor of your choice and add a line like 
```
17 *	* * *	root    cd / && run-parts --report /etc/cron.hourly
```
then restart `sudo service cron restart`
Next you can check `sudo service cron status` and then `crontab -l` returns
```
17 *	* * *	root    cd / && run-parts --report /etc/cron.hourly
```

If you need to setup crontab for root, you can use `sudo crontab -e` or if it's for another user then `crontab -u`

Also check if you have this file
```
cat /etc/crontab 
# /etc/crontab: system-wide crontab
# Unlike any other crontab you don't have to run the `crontab'
# command to install the new version when you edit this file
# and files in /etc/cron.d. These files also have username fields,
# that none of the other crontabs do.

SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin

# Example of job definition:
# .---------------- minute (0 - 59)
# |  .------------- hour (0 - 23)
# |  |  .---------- day of month (1 - 31)
# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# |  |  |  |  |
# *  *  *  *  * user-name command to be executed
17 *	* * *	root    cd / && run-parts --report /etc/cron.hourly
25 6	* * *	root	test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.daily )
47 6	* * 7	root	test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly )
52 6	1 * *	root	test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.monthly )
#

```

Answer

Thank you Sri for your detailed response! For your local `crontab -e` example, I don't think you want to specify the user. After seeing your post, I tried `crontab -e` again and installed a `* * * * *` test script to echo the date into a test file and it worked. I was able to see the test file and the date written inside was updated every minute.

Unfortunately, when I change it specify the hour and minute, the scheduled job does not run. I suspect this is due to time zone issue so I added a `CRON_TZ=America/Los_Angeles` in my crontab for PST time zone. That didn't work either. Then I tried scheduling using UTC time and that worked....

So, how do I change the time zone for crontab? My system time is already set to PST. I see it when I type `date` in the shell. The man page for cron says "The daemon will use, if present, the definition from /etc/timezone for the timezone." when I `cat /etc/timezone` it says "America/Los_Angeles".

I'm not sure why there's a time zone mismatch.

Cron jobs on Ubuntu EC2 Instance

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