Linux Crontab Syntax

# write existing crontab to file
crontab -l > crontab.out
# put a file with crontab entries in it into crontab
crontab crontab.out

# By default, it will edit crontab entries of current logged in user. To edit other user crontab use command as below
crontab -e
crontab -u username -e

# How to List Crontab
# To view crontab entries of current user use the following command.

#Use -u followed by username to view crontab entries of the specified user.
crontab -l
crontab -u username -l

* * * * * YOURCOMMAND
– – – – –
| | | | |
| | | | +—– Day in Week (0 to 7) (Sunday is 0 and 7)
| | | +——- Month (1 to 12)
| | +——— Day in Month (1 to 31)
| +———– Hour (0 to 23)
+————- Minute (0 to 59)

Linux crontab has six fields. 1-5 fields defines the date and time of execution. The 6'th fields are used for command or script to be executed.The Linux crontab syntax are as following:

[Minute] [hour] [Day_of_the_Month] [Month_of_the_Year] [Day_of_the_Week] [command]

Astrics (*) - Matches anything
Define range - You can define range using the hypen like: 1-10 or 20-30 or sun-fri or feb-apr
Define multiple range - You can define multiple ranges in a given field with comma separated stuff like: jan-mar,jul-sep

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