Linux Basic — crontab Syntax

crontab Syntax

A crontab entry has five time fields followed by the command to run.

# ┌───────────── minute (0–59)
# │ ┌───────────── hour (0–23)
# │ │ ┌───────────── day of month (1–31)
# │ │ │ ┌───────────── month (1–12)
# │ │ │ │ ┌───────────── day of week (0–7, 0 and 7 = Sunday)
# │ │ │ │ │
# * * * * * command-to-execute

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Examples

# every minute
* * * * * /opt/check.sh

# daily at 2:30 AM
30 2 * * * /opt/backup.sh

# every Monday at 9 AM
0 9 * * 1 /opt/weekly-report.sh

# first day of every month at midnight
0 0 1 * * /opt/monthly-cleanup.sh

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Field Values

Field	Range	Special
minute	0–59
hour	0–23
day	1–31
month	1–12	or jan–dec
weekday	0–7	0 and 7 = Sun, or sun–sat

* means “every value” for that field.

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Common Pitfalls

• Both day and weekday specified → cron runs if either matches (OR, not AND)
• Percent signs (%) in the command are interpreted as newlines — escape with \%
• Environment is minimal — no $PATH from your shell, no aliases

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Next → cron Expressions