DevOps
Reference material for developers working with infrastructure and automation. Cron expressions, scheduling patterns, and system tools explained with real-world examples.
Cron Job Not Running? A Field-Tested Debugging Checklist
A checklist for cron jobs that never fire or run at the wrong time: logs, environment differences, the % gotcha, missing newlines and DST skips.
Cron Expressions: A Complete Guide to Scheduling Syntax
Cron syntax in full: the five fields, special characters, predefined schedules, timezone pitfalls, cloud schedulers and the mistakes that bite most.
Scheduling, and Why It Silently Stops Working
Cron is the rare piece of infrastructure that fails without telling anyone. The job does not crash, it simply never runs, and you find out from a customer. These two pieces cover the syntax and the debugging in that order.
Cron expressions
covers the five fields properly, including the step and range characters people copy without reading, the predefined
shorthands, and the timezone behaviour that differs between system cron and every cloud scheduler. It also flags the
sixth-field trap: /etc/crontab and files under /etc/cron.d take a user column that a personal
crontab does not, so a working line breaks when you move it.
The debugging checklist
is the one to open when something is already broken. It goes through where the logs actually are on Debian and RHEL,
the minimal PATH cron gives you compared with your login shell, the unescaped % that truncates
a command, the missing trailing newline that makes the last line vanish, and the DST transitions that skip or repeat a
run once a year.
Build and check expressions in the crontab generator - it previews the next run times, which catches most mistakes faster than reading the syntax back to yourself.