# Scheduling Processes * All the processes are started when systems boots or when a command is run. * Processes/commands can be scheduled to be executed at a specific time on a specific date by using the **`cron`** daemon. ## Commands ### crontab * **`crontab`** - maintain crontab files for individual users * A **crontab** file contains instructions for the [**cron**](https://crontab.guru/cron.8.html) daemon * `crond` - daemon to execute scheduled commands * Each user can define their own crontab and the commands are executed under the user who owns that particular crontab ```bash # Systems level crontabs less /etc/crontab # /etc/crontab: system-wide crontab # Unlike any other crontab you don't have to run the `crontab' # command to install the new version when you edit this file # and files in /etc/cron.d. These files also have username fields, # that none of the other crontabs do. SHELL=/bin/sh # You can also override PATH, but by default, newer versions inherit it from the environment #PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin # Example of job definition: # .---------------- minute (0 - 59) # | .------------- hour (0 - 23) # | | .---------- day of month (1 - 31) # | | | .------- month (1 - 12) OR jan,feb,mar,apr ... # | | | | .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat # | | | | | # * * * * * user-name command to be executed 17 * * * * root cd / && run-parts --report /etc/cron.hourly 25 6 * * * root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.daily ) 47 6 * * 7 root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly ) 52 6 1 * * root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.monthly ) # # anacron runs processes on a set schedule (hourly, daily, weekly, monthly) ls -lah /etc/cron.daily/ total 56K drwxr-xr-x 2 root root 4,0K ott 5 09:09 . drwxr-xr-x 135 root root 12K nov 3 21:47 .. -rwxr-xr-x 1 root root 311 lug 16 2019 0anacron -rwxr-xr-x 1 root root 376 dic 4 2019 apport -rwxr-xr-x 1 root root 1,5K lug 28 09:26 apt-compat -rwxr-xr-x 1 root root 355 dic 29 2017 bsdmainutils.dpkg-remove -rwxr-xr-x 1 root root 384 nov 19 2019 cracklib-runtime -rwxr-xr-x 1 root root 123 dic 5 2021 dpkg -rwxr-xr-x 1 root root 377 gen 21 2019 logrotate -rwxr-xr-x 1 root root 1,3K mar 17 2022 man-db -rw-r--r-- 1 root root 102 feb 13 2020 .placeholder -rwxr-xr-x 1 root root 652 dic 7 2020 plocate # Every script is own by root, since they are associated to system-wide processes ``` ```bash crontab -e # Edit user's crontab in a text editor (chose prefered text editor at first run) # Expression Syntax: m h dom mon dow command # m = minutes (0-59) # h = hours (0-23) # dom = day of the month (1-31) # mon = month (1-12) # dow = day of the week (0-6, sunday=0, saturday=6) # command to run according to the schedule crontab -l # List user's crontab crontab -r # Remove the current user's crontab # List all user's crontabs sudo su for user in $(cut -f1 -d: /etc/passwd); do echo $user; crontab -u $user -l; done ``` > πŸ“Œ Check the [**crontab.guru**](https://crontab.guru/) editor for cron schedule expressions. ## Boot Process * **`/etc/init.d`** - contains start/stop scripts for various services, while booting and shutting down the system * **init** (short for initialization) is the program that spawns all other processes. It runs as a daemon and typically has PID 1. * The applications that are started by init are located in the **`/etc/rc.d`** folder. Within this directory there is a separate folder for each run level, eg *rc0.d*, *rc1.d*, and so on. ```bash ls -lah /etc/init.d/ total 184K drwxr-xr-x 2 root root 4,0K ott 28 22:52 . drwxr-xr-x 135 root root 12K nov 3 21:47 .. -rwxr-xr-x 1 root root 2,3K nov 28 2019 acpid -rwxr-xr-x 1 root root 5,5K nov 5 2019 alsa-utils -rwxr-xr-x 1 root root 2,1K lug 16 2019 anacron -rwxr-xr-x 1 root root 3,7K apr 1 2020 apparmor -rwxr-xr-x 1 root root 2,9K mag 10 15:23 apport -rwxr-xr-x 1 root root 2,4K ago 21 2018 avahi-daemon -rwxr-xr-x 1 root root 2,9K feb 26 2020 bluetooth -rwxr-xr-x 1 root root 1,3K mar 27 2020 console-setup.sh -rwxr-xr-x 1 root root 3,0K mar 18 2021 cron -rwxr-xr-x 1 root root 2,8K feb 17 2020 cups -rwxr-xr-x 1 root root 2,0K apr 10 2020 cups-browsed -rwxr-xr-x 1 root root 3,1K set 30 2019 dbus -rwxr-xr-x 1 root root 3,0K apr 21 2022 gdm3 -rwxr-xr-x 1 root root 985 gen 13 2021 grub-common -rwxr-xr-x 1 root root 1,8K feb 21 2022 hwclock.sh -rwxr-xr-x 1 root root 2,6K dic 13 2019 irqbalance -rwxr-xr-x 1 root root 3,1K mag 19 2017 kerneloops -rwxr-xr-x 1 root root 1,5K nov 27 2019 keyboard-setup.sh -rwxr-xr-x 1 root root 2,0K feb 19 2020 kmod -rwxr-xr-x 1 root root 695 gen 28 2020 lvm2 -rwxr-xr-x 1 root root 586 gen 28 2020 lvm2-lvmpolld -rwxr-xr-x 1 root root 1,9K set 29 2020 open-vm-tools -rwxr-xr-x 1 root root 9,0K dic 3 2018 openvpn -rwxr-xr-x 1 root root 1,4K feb 23 2022 plymouth -rwxr-xr-x 1 root root 760 feb 23 2022 plymouth-log -rwxr-xr-x 1 root root 959 feb 25 2022 procps -rwxr-xr-x 1 root root 469 ott 15 2020 pulseaudio-enable-autospawn -rwxr-xr-x 1 root root 4,4K ott 15 2019 rsync -rwxr-xr-x 1 root root 2,2K feb 11 2020 saned -rwxr-xr-x 1 root root 2,0K gen 12 2020 speech-dispatcher -rwxr-xr-x 1 root root 2,5K set 27 2019 spice-vdagent -rwxr-xr-x 1 root root 6,8K giu 27 20:28 udev -rwxr-xr-x 1 root root 2,1K gen 21 2020 ufw -rwxr-xr-x 1 root root 1,4K lug 21 2020 unattended-upgrades -rwxr-xr-x 1 root root 1,3K lug 21 2020 uuidd -rwxr-xr-x 1 root root 485 ago 11 2018 whoopsie -rwxr-xr-x 1 root root 2,7K ott 19 2021 x11-common ls -d /etc/rc* /etc/rc0.d /etc/rc1.d /etc/rc2.d /etc/rc3.d /etc/rc4.d /etc/rc5.d /etc/rc6.d /etc/rcS.d man runlevel # Mapping between runlevels and systemd targets β”Œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”¬β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β” β”‚Runlevel β”‚ Target β”‚ β”œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”Όβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€ β”‚0 β”‚ poweroff.target β”‚ β”œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”Όβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€ β”‚1 β”‚ rescue.target β”‚ β”œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”Όβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€ β”‚2, 3, 4 β”‚ multi-user.target β”‚ β”œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”Όβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€ β”‚5 β”‚ graphical.target β”‚ β”œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”Όβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€ β”‚6 β”‚ reboot.target β”‚ β””β”€β”€β”€β”€β”€β”€β”€β”€β”€β”΄β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”˜ ls -lah /etc/rc5.d/ total 16K drwxr-xr-x 2 root root 4,0K set 12 23:06 . drwxr-xr-x 135 root root 12K nov 3 21:47 .. lrwxrwxrwx 1 root root 27 apr 13 2021 K01speech-dispatcher -> ../init.d/speech-dispatcher lrwxrwxrwx 1 root root 15 apr 13 2021 S01acpid -> ../init.d/acpid lrwxrwxrwx 1 root root 17 apr 13 2021 S01anacron -> ../init.d/anacron lrwxrwxrwx 1 root root 16 apr 13 2021 S01apport -> ../init.d/apport lrwxrwxrwx 1 root root 22 apr 13 2021 S01avahi-daemon -> ../init.d/avahi-daemon lrwxrwxrwx 1 root root 19 apr 13 2021 S01bluetooth -> ../init.d/bluetooth lrwxrwxrwx 1 root root 26 apr 13 2021 S01console-setup.sh -> ../init.d/console-setup.sh lrwxrwxrwx 1 root root 14 apr 13 2021 S01cron -> ../init.d/cron [...] lrwxrwxrwx 1 root root 29 apr 13 2021 S01unattended-upgrades -> ../init.d/unattended-upgrades lrwxrwxrwx 1 root root 15 apr 13 2021 S01uuidd -> ../init.d/uuidd lrwxrwxrwx 1 root root 18 apr 13 2021 S01whoopsie -> ../init.d/whoopsie ``` *** --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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