Why does an ack‑based cron job fail after applying CIS Benchmarks on AlmaLinux 8?

When a command like ack works in an interactive shell but fails in a cron job after applying CIS (Center for Internet Security) Benchmarks, the discrepancy is typically caused by the difference between the interactive user environment and the restricted cron environment.

Assumptions

• The ack binary is installed in a location not included in the default cron PATH (e.g., /usr/local/bin).
• CIS Benchmarks have been applied, which often involve tightening permissions, restricting environment variables, or modifying shell profiles.
• The cron job is executing without a full login shell, meaning .bashrc or .bash_profile are not sourced.

Root Cause Analysis

CIS Benchmarks often enforce strict PATH settings and remove unnecessary environment variables to reduce the attack surface. While your interactive shell loads a comprehensive PATH from your profile, crond typically uses a very minimal PATH (often just /usr/bin:/bin). If ack is located elsewhere, the cron job cannot find the executable, resulting in a failure that may manifest as "zero matches" if the script ignores the "command not found" error.

Resolution Steps

1. Identify the absolute path: Run which ack in your interactive shell to find the full path (e.g., /usr/local/bin/ack).
2. Update the Cron Job: Use the absolute path in your crontab entry instead of the shorthand command.
   Example: Change ack "pattern" /var/log/app.log to /usr/local/bin/ack "pattern" /var/log/app.log.
3. Alternative: Define PATH in Crontab: Add a PATH definition at the top of your crontab file to ensure all tools are reachable.
   PATH=/usr/local/bin:/usr/bin:/bin

Verification and Rollback

• Verification: Redirect the cron output to a log file (e.g., >> /tmp/cron_debug.log 2>&1) to confirm that "command not found" errors have disappeared and matches are being returned.
• Rollback: If the change causes unexpected behavior, revert the crontab entry to the previous version using crontab -e.