2 - Raspberry PI Community Projects

Be careful, however, if the order in which the different scheduled tasks and
the delay between their respective executions maers, you should check the
compatibility of these constraints with cron's behavior; if necessary, you can
prepare a special schedule for the two problematic nights per year.
Each significant line of a crontab describes a scheduled command with the six (or seven) following
fields:
• the value for the minute (number from 0 to 59);
• the value for the hour (from 0 to 23);
• the value for the day of the month (from 1 to 31);
• the value for the month (from 1 to 12);
• the value for the day of the week (from 0 to 7, 1 corresponding to Monday, Sunday being
represented by both 0 and 7; it is also possible to use the first three letters of the name of
the day of the week in English, such as Sun, Mon, etc.);
• the user name under whose identity the command must be executed (in the /etc/
crontab file and in the fragments located in /etc/cron.d/, but not in the users' own
crontab files);
• the command to execute (when the conditions defined by the first five columns are met).
All these details are documented in the crontab(5) man page.
Each value can be expressed in the form of a list of possible values (separated by commas). The
syntax a-b describes the interval of all the values between a and b. The syntax a-b/c describes
the interval with an increment of c (example: 0-10/2 means 0,2,4,6,8,10). An asterisk * is a
wildcard, representing all possible values.
#Format
#min hour day mon dow
command
# Download data every night at 7:25 pm
25 19 * * * $HOME/bin/get.pl
# 8:00 am, on weekdays (Monday through Friday)
00 08 * * 1-5 $HOME/bin/dosomething
206 The Debian Administrator's Handbook