Systemd

Replaces initd. It should be more efficient. Honestly I don't see the benefits.

It also provides timed execution like cron does equally well.

The service command invoke script in /etc/init.d.

service --status-all

Run all scripts with the 'status' option. Tells you which services are up.

systemctl list-units

Show all known units. Alternative for service --status-all that does not work on modern RedHat versions.

systemctl list-timers

Show all active timers

E.g for certbot (letsencrypt)

$ systemctl list-timers
NEXT                        LEFT         LAST                        PASSED UNIT                         ACTIVATES
do 2018-11-29 00:00:00 CET  2h 5min left wo 2018-11-28 12:00:01 CET  9h ago certbot.timer                certbot.service

2 timers listed.
Pass --all to see loaded but inactive timers, too.

$ cat /lib/systemd/system/certbot.timer
[Unit]
Description=Run certbot twice daily

[Timer]
OnCalendar=*-*-* 00,12:00:00
Persistent=true

[Install]
WantedBy=timers.target

$ cat /lib/systemd/system/certbot.service 
[Unit]
Description=Certbot
Documentation=file:///usr/share/doc/python-certbot-doc/html/index.html
Documentation=https://letsencrypt.readthedocs.io/en/latest/
[Service]
Type=oneshot
ExecStartPre=/usr/bin/perl -e 'sleep int(rand(3600))'
ExecStart=/usr/bin/certbot -q renew
PrivateTmp=true

systemctl daemon-reload

After changing a configuration file reload it

systemctl mask UNIT>

Link the timer to /dev/null effectively disabling it