Each entry in a crontab must end with a character

D

The answer is D, newline.

Crontab is a file used in Linux and other Unix-like operating systems to schedule and automate the execution of commands or scripts at specified times. It contains a list of commands and the times at which they should be run. Each line in the crontab file represents a job, and the entries are separated by newline characters.

When you add a new job to a crontab file, you must make sure to end the entry with a newline character. This is important because the cron daemon, which is responsible for running the scheduled jobs, reads the crontab file line by line and uses the newline character to determine where one entry ends and the next one begins.

If you forget to include a newline character at the end of an entry, the cron daemon may not be able to parse the crontab file correctly, which could cause your scheduled jobs to fail to run. So it's important to always include a newline character at the end of each entry in your crontab file.

To edit a crontab file, you can use the "crontab -e" command, which will open the file in your default text editor. Once you've made your changes, save the file and exit the editor, and the new crontab file will be installed automatically.