server - Start script on system startup (Ubuntu 16.04.1) - Ask Ubuntu

on new ubuntu system tried start bash script automatically on system start up.

i found lot of posts , how-to's it. tried make via crontab:

• run crontab -e
• add @reboot /cronjobs/demo.sh >> /cronjobs/cronlogs/demo.output
• set execution permission script sudo chmod +x /cronjobs/demo.sh
• reboot system

the output created, script not execute. tried solution rc.local file:

• run sudo vi /etc/rc.local
• added /cronjobs/demo.sh || exit 1
• reboot system

but script doesn't run. read reboot script must in /etc/rc0.d/. tried this:

• move script mv /cronjobs/demo.sh /etc/rc0.d/k99_demo.sh
• check permissions (all seems ok)
• reboot system

same thing - script not executed.

so, what's error? why script can't executed? can execute script if run ./demo.sh after switched folder cd /cronjobs . script demo-file creates folder:

 #!/bin/sh echo demo output mkdir /cronjobs/demofolder 

edited: replaced paths , filenames; added full content of demo.sh file

the easiest solution using sudo powers create file in /etc/cron.d/:

shell=/bin/sh path=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin @reboot   root    mkdir /cronjobs @reboot   root    sleep 10 @reboot   root    mkdir /cronjobs/demofolder 

this avoids use of script file altogether , works users regardless of home directory name, ie /home/steve, /home/mary, etc.

edit - add sleep 10

for whatever reason cron working fast, or kernel working slow when making directories. line sleep 10 necessary between 2 mkdir lines.

you may not need 10 seconds in between 2 make directory commands 10 works on system ssd.

edit 2 - make full directory path in 1 command

as per comments below simpler method use:

shell=/bin/sh path=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin @reboot   root    mkdir -p -v /cronjobs/demofolder 

• -p (long version --parents) tells mkdir automatically create directory parent levels if don't exist.
• -v (long version --verbose) tells mkdir print names of directories created.