Linux CLI - Cron and Scheduling
How would you write a crontab entry to run a backup script at 11:59 PM on the last day of every month?
How would you write a crontab entry to run a backup script at 11:59 PM on the last day of every month?
hard📝 Application Q9 of 15
Step-by-Step Solution
Solution:
Step 1: Understand last day of month challenge
Crontab cannot directly specify last day; use days 28-31 and test if tomorrow is day 1.Step 2: Analyze 59 23 28-31 * * [ $(date -d tomorrow +\%d) = 01 ] && /path/backup.sh
Runs at 23:59 on days 28-31 and uses shell test to check if next day is 1, meaning last day.Final Answer:
59 23 28-31 * * [ $(date -d tomorrow +\%d) = 01 ] && /path/backup.sh -> Option DQuick Check:
Use day range + shell test for last day detection [OK]
Quick Trick: Use day 28-31 plus shell test for last day [OK]
Common Mistakes:
- Using day 31 only (fails for months with fewer days)
- Misusing day of week field
- Ignoring shell test necessity
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