Scheduled tasks across accounts.
WHERE CRONTABS LIVE
One per user, stored by the system rather than edited directly.
HOW TO EDIT ANOTHER USER'S
crontab with the user option, as root.
WHY NOT EDIT THE STORED FILE
Cron may not notice, and the format is validated on edit.
WHAT SYSTEM CRON DIRECTORIES ARE
Locations where files run on an hourly, daily, weekly or monthly basis.
WHAT DIFFERS THERE
The file includes a user column.
WHY THAT CATCHES PEOPLE
Copying a user crontab line into a system file fails, because the command is read as a username.
HOW TO LIST EVERY SCHEDULED TASK ON A SERVER
Iterate over accounts, listing each crontab, plus the system directories.
WHY THAT MATTERS
Unknown scheduled tasks are a common persistence route after a compromise, and a common source of load.
WHAT TO CHECK ON A BUSY SERVER
Whether many jobs are scheduled at the same minute.
WHY
Everything at the top of the hour produces a spike.
WHAT TO DO
Spread them across the hour.
WHAT TO SET FOR REPORTING
An address to receive output, or explicit logging.
WHAT TO REVIEW PERIODICALLY
Every scheduled task, and whether it is still needed.
WHAT TO REMOVE
Jobs for accounts that no longer exist.
