Debian – Cronjob executing multiple times at once

A few things occur to me while reading this.

If you are running bash echoing the value of $BASH should expand to the full path and filename of the bash executable in use.

How are you calling date in your script. Are you calling it with the full path name or as "date". The later case can result in the use of function, aliases, or whatever happens to be first in the path rather than the date program you expect.

Bash will behave differently in some cases depending on the environment. You may want to dump the environment to a file from the script and look at it running from the command-line and from cron. You may find that the PATH is different or that some other environment variable is set differently. You should be able to dump this to a file in /tmp by putting a line like "env > /tmp/environment.$$" in the script. Each time the script is run it will print out the environment to a file named environment.(pid of script)

You can set also the shell for the entire crontab to whichever shell you want by using "SHELL=/path/to/new/shell" on a line by itself.

Check stat cron is running

status cron 
cron start/running, process 1380

or

ps aux | grep cron
root      1380  0.0  0.0   2092   876 ?        Ss   Nov03   0:02 cron

If it's running or not then have a look in /var/log/syslog and see if there are any relevant messages.

grep CRON /var/log/syslog
Nov  9 11:18:29 iain-ubuntu cron[3509]: (CRON) STARTUP (fork ok)
Nov  9 11:18:29 iain-ubuntu cron[3509]: (CRON) INFO (Skipping @reboot jobs -- not system startup)