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Troubleshooting Cron on EC2, which required both a permissions and a time zone fix.

2015-01-14 - Troubleshooting Cron on EC2

Today I had trouble getting a cron job to work.

The cron command was:

# run the lunchbot every weekday at 12:30 pm
30 12 * * 1-5 /home/ubuntu/bothouse/lunchbot/cron.sh > /home/ubuntu/bothouse/lunchbot/cron.log

The first problem, I discovered, was that cron.sh didn't have permissions set to be executable by the user (ubuntu).

ls -l

total 16
-rw-rw-r-- 1 ubuntu ubuntu    0 Jan 14 13:09 cron.log
-rw-rw-r-- 1 ubuntu ubuntu  164 Jan 14 12:44 cron.sh
-rw-rw-r-- 1 ubuntu ubuntu 1078 Jan 14 11:09 LICENSE
-rw-rw-r-- 1 ubuntu ubuntu 4062 Jan 14 13:07 lunchbot.js
-rw-rw-r-- 1 ubuntu ubuntu  254 Jan 14 11:09 README.md

I fixed that with chmod

chmod u+x cron.sh

In later cases, I also had to make sure cron.log was available with:

chmod u+x cron.log

Ok, then after some testing, I realized that cron was using UTC time, not local time to the machine (US East Coast).

Googling around, I found out how to set the time zone for the EC2 box:

echo "America/New_York" | sudo tee /etc/timezone
sudo dpkg-reconfigure --frontend noninteractive tzdata

According to the documentation, this will also adjust for Daylight Saving Time, which is pretty cool -- and wouldn't have happened if I just used UTC and offset the hours.

So now checking the date gets:

date
Wed Jan 14 12:59:32 EST 2015

BUT! I also discovered that cron doesn't use that UNTIL YOU REBOOT.

So I rebooted my EC2 instance from the AWS dashboard, and now all works as expected.

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