Difference between revisions of "Cron Notes"
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# month 1-12 (or names, see below) | # month 1-12 (or names, see below) | ||
# day of week 0-7 (0 or 7 is Sun, or use names) | # day of week 0-7 (0 or 7 is Sun, or use names) | ||
| − | # A field may be an asterisk (*), which always stands for | + | # A field may be an asterisk (*), which always stands for "first-last". |
# | # | ||
# Ranges of numbers are allowed. Ranges are two numbers separated with a hyphen. | # Ranges of numbers are allowed. Ranges are two numbers separated with a hyphen. | ||
| − | # The specified range is inclusive. For example, 8-11 for an | + | # The specified range is inclusive. For example, 8-11 for an "hours" entry |
# specifies execution at hours 8, 9, 10 and 11. | # specifies execution at hours 8, 9, 10 and 11. | ||
# | # | ||
# Lists are allowed. A list is a set of numbers (or ranges) separated by commas. | # Lists are allowed. A list is a set of numbers (or ranges) separated by commas. | ||
| − | # Examples: | + | # Examples: "1,2,5,9", "0-4,8-12". |
# | # | ||
# Step values can be used in conjunction with ranges. Following a range with | # Step values can be used in conjunction with ranges. Following a range with | ||
| − | # | + | # "/<number>" specifies skips of the number's value through the range. |
| − | # For example, | + | # For example, "0-23/2" can be used in the hours field to specify command |
# execution every other hour (the alternative in the V7 standard is | # execution every other hour (the alternative in the V7 standard is | ||
| − | # | + | # "0,2,4,6,8,10,12,14,16,18,20,22"). Steps are also permitted after an |
| − | # asterisk, so if you want to say | + | # asterisk, so if you want to say "every two hours", just use "*/2". |
| + | # Note: The day of a command's execution can be specified by two fields | ||
| + | # -- day of month, and day of week. If both fields are restricted | ||
| + | # (that is, are not *), the command will be run when either field matches the | ||
| + | # current time. For example, "30 4 1,15 * 5" would cause a command | ||
| + | # to be run at 4:30 am on the 1st and 15th of each month, plus every Friday. | ||
| + | # | ||
| + | # The "sixth" field (the rest of the line) specifies the command to be | ||
| + | # run. The entire command portion of the line, up to a newline or % | ||
| + | # character, will be executed by /bin/sh or by the shell specified in the | ||
| + | # SHELL variable of the crontab file. Percent-signs (%) in the command, | ||
| + | # unless escaped with backslash (\), will be changed into newline characters, | ||
| + | # and all data after the first % will be sent to the command as standard input. | ||
| + | # There is no way to split a single command line onto multiple lines, | ||
| + | # ala the shell's trailing "\". | ||
# | # | ||
# Example system /etc/crontab excerpt: | # Example system /etc/crontab excerpt: | ||
# # run five minutes after midnight, every day | # # run five minutes after midnight, every day | ||
| − | # 5 0 * * * root | + | # 5 0 * * * root /usr/sbin/ntpdate time.nist.gov >> /var/log/ntpdate.log 2>&1 |
| − | # # run at 2:15pm on the first of every month | + | # # run at 2:15pm on the first of every month |
| − | # 15 14 1 * * root | + | # 15 14 1 * * root /bin/foo > /dev/null 2>&1 |
| − | # # run at | + | # # run at 11 pm on weekdays |
| − | # 0 | + | # 0 23 * * 1-5 root mail -s "It's 11pm" joe%Joe,%%Where are your kids?% |
# 23 0-23/2 * * * root echo "run 23 minutes after midn, 2am, 4am ..., everyday" | # 23 0-23/2 * * * root echo "run 23 minutes after midn, 2am, 4am ..., everyday" | ||
# 5 4 * * sun root echo "run at 5 after 4 every sunday" | # 5 4 * * sun root echo "run at 5 after 4 every sunday" | ||
</pre> | </pre> | ||
Revision as of 19:31, 31 January 2007
I have huge, horrible, complex cron files. I stick this big comment at the top of the /etc/crontab file so I don't have to keep going back to the man page.
# The time and date fields are: # field allowed values # ----- -------------- # minute 0-59 # hour 0-23 # day of month 1-31 # month 1-12 (or names, see below) # day of week 0-7 (0 or 7 is Sun, or use names) # A field may be an asterisk (*), which always stands for "first-last". # # Ranges of numbers are allowed. Ranges are two numbers separated with a hyphen. # The specified range is inclusive. For example, 8-11 for an "hours" entry # specifies execution at hours 8, 9, 10 and 11. # # Lists are allowed. A list is a set of numbers (or ranges) separated by commas. # Examples: "1,2,5,9", "0-4,8-12". # # Step values can be used in conjunction with ranges. Following a range with # "/<number>" specifies skips of the number's value through the range. # For example, "0-23/2" can be used in the hours field to specify command # execution every other hour (the alternative in the V7 standard is # "0,2,4,6,8,10,12,14,16,18,20,22"). Steps are also permitted after an # asterisk, so if you want to say "every two hours", just use "*/2". # Note: The day of a command's execution can be specified by two fields # -- day of month, and day of week. If both fields are restricted # (that is, are not *), the command will be run when either field matches the # current time. For example, "30 4 1,15 * 5" would cause a command # to be run at 4:30 am on the 1st and 15th of each month, plus every Friday. # # The "sixth" field (the rest of the line) specifies the command to be # run. The entire command portion of the line, up to a newline or % # character, will be executed by /bin/sh or by the shell specified in the # SHELL variable of the crontab file. Percent-signs (%) in the command, # unless escaped with backslash (\), will be changed into newline characters, # and all data after the first % will be sent to the command as standard input. # There is no way to split a single command line onto multiple lines, # ala the shell's trailing "\". # # Example system /etc/crontab excerpt: # # run five minutes after midnight, every day # 5 0 * * * root /usr/sbin/ntpdate time.nist.gov >> /var/log/ntpdate.log 2>&1 # # run at 2:15pm on the first of every month # 15 14 1 * * root /bin/foo > /dev/null 2>&1 # # run at 11 pm on weekdays # 0 23 * * 1-5 root mail -s "It's 11pm" joe%Joe,%%Where are your kids?% # 23 0-23/2 * * * root echo "run 23 minutes after midn, 2am, 4am ..., everyday" # 5 4 * * sun root echo "run at 5 after 4 every sunday"
