Cron

Question 1

crontab

Answer 1

Used to view and edit user cron table file
In /etc/cron.hourly 
/etc/cron.daily
/etc/cron.weekly
/etc/cron.monthly
/etc/cron.d: whole system
/etc/cron.deny: lists users restricted from cron jobs.
-e: edit
-l: list
-r: remove
-u: for specified user.

Question 2

Cron job formatting

Answer 2

Minute, hour, day of month, month, day of week, username, command.
Ex: 0 5 * * sat (or 6)

Question 3

at

Answer 3

One time job at specified time. enters text editor by default which can be exited via Ctrl+d
-f: file path for script with time after.
Ex: now +5 minutes
9:30 PM Tuesday

Question 4

atq

Answer 4

View job queue

Question 5

atrm

Answer 5

Remove numbered job.

Question 6

at.allow and at.deny

Answer 6

In /etc/

Determines which users can set at jobs.

Question 7

Transient Timers

Answer 7

Setup by systemd-run command. Do not require service file.

Question 8

Timer unit files

Answer 8

[Timer]
Monotonic On BootSec=, OnUnitActiveSec=
Realtime OnCalendar=
Unit=
[Install]
WantedBy=timers.target

Question 9

systemctl list-timers =all

Answer 9

Lists all timers on systems

Note: can also view systemctl cat

Question 10

systemd-run -onactive=

Answer 10

Can create transient timer, does not require service file.