Can't get crontab to work as expected

I want to do a daily backup of my home directory by executing the following script (I can write to /home):

   #!/bin/sh -e
   cd /home
   ls -l 
   rm -f silbar.tar.gz
   echo "starting tar"
   tar -czf silbar.tar.gz silbar
   cd ./silbar
   echo "done with tar"
   beep

To do so I created my personal crontab file by enter ~$ crontab -e and added the following (and only line which is not a comment)

30 6 * * * mybackup.script 

assuming that my crontab would run in my home directory.

But nothing happens. Doing ~$ grep CRON /var/log/syslog shows, apart from root things, the following error:

Aug 30 06:30:01 Puma CRON[100126]: (silbar) CMD (mybackup.script )

Aug 30 06:30:01 Puma CRON[100125]: (CRON) info (No MTA installed, discarding output)

So, what am I doing wrong? What is MTA, anyway?

You may need to enter the full path of your script in your cronjob.

Cronjobs run with an almost empty environment. Thus, executables may not be found. The same goes for the commands in the script: provide full paths to commands, or set up a PATH variable in your script.

By beginning with #!/bin/sh -e, you cause your script to run with sh (bashis better IMHO), and -e exits on any error (man set), so one cannot handle errors. Your script is failing, and cron is trying to email you the log. cron can't find a Message Transfer Agent (MTA). Email hasn't been configured on your system, even for local delivery.

Jobs run through cron, or systemd startup scripts aren't run in the same runtime environment that you have on your desktop. systemd startup scripts are run as root. None of your PATH changes, or other environment variable settings from ~/.bashrc are automatically propagated to your cron job. For example, there's no $DISPLAY, so GUI programs need special treatment (read man xhost).

One can set environment variables for all one's cron jobs in the crontab file Read man 5 crontab.

Look at the results of echo "=== id ===";id;echo "=== set ===";set;echo "=== env ===";env | sort;echo "=== alias ===";alias in each of your environments.

Since the command part of the crontab line is, by default, interpreted by /bin/sh, which has a simpler syntax than /bin/bash, I recommend having command be a call to a bash script (executable, mounted, starts with #!/bin/bash) which sets up the environment, then calls the desired program.

Wow!, very useful answers from user535733, Rinzwind, Vanadium, and waltinator. I now have it working as suggested, using bash and full paths. The backup now goes to a flash drive (which is where I wanted it to go, anyway) instead of to /home.

Thanks to all, Dick