etccronallow

etccronallow refers to the file /etc/cron.allow in Unix-like operating systems, a simple access control list used by the cron daemon to determine which users may use the crontab command to schedule tasks. It is part of a two-file mechanism that works with /etc/cron.deny to manage cron permissions.

The basic behavior is as follows: If /etc/cron.allow exists, only users listed in that file are permitted to run crontab. If a user is not listed, access is denied. If /etc/cron.allow does not exist but /etc/cron.deny exists, being listed in cron.deny denies access, while all other users are allowed. If neither file exists, crontab is typically allowed for all users, subject to the system’s general permissions.

Files usually contain one username per line, with comments (lines beginning with #) ignored and blank lines skipped. Whitespace around usernames is ignored, and duplicate entries have no additional effect.

Notes and caveats: This mechanism originates from older cron implementations (such as Vixie/ISC cron) and may behave differently on some systems or be superseded by other access controls (e.g., PAM, systemd timers). Administrators should ensure these files are secured (generally readable by root only) and kept up to date, as misconfigurations can unintentionally grant or revoke cron scheduling rights. Example operations include adding or removing users by editing or appending to /etc/cron.allow or /etc/cron.deny as appropriate.