SIMULATION -
In which file, if present, must all users be listed that are allowed to use the cron scheduling system? (Specify the full name of the file, including path.)
/etc/cron.allow
The file in which all users must be listed that are allowed to use the cron scheduling system is the "/etc/cron.allow" file.
The cron daemon allows system administrators to schedule tasks to run automatically at specified times or intervals. The cron system uses two files to manage access: "/etc/cron.allow" and "/etc/cron.deny".
If the "/etc/cron.allow" file exists, then only users listed in that file are allowed to use the cron system. If the file does not exist, then the "/etc/cron.deny" file is checked. If a user's name is listed in the "/etc/cron.deny" file, they are not allowed to use the cron system. If neither file exists, then only the root user is allowed to use the cron system.
It is important to note that the "/etc/cron.allow" and "/etc/cron.deny" files use a whitelist/blacklist approach, respectively. This means that if a user's name is not listed in either file, they are still allowed to use the cron system.
To add a user to the "/etc/cron.allow" file, simply add their username to a new line in the file. To remove a user from the file, simply delete their username from the file.
It is also important to ensure that the permissions on these files are set correctly. The "/etc/cron.allow" file should be owned by root and only writable by root. The "/etc/cron.deny" file should also be owned by root and only writable by root. Improper file permissions can compromise the security of the cron system.