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I can't find answer to my question: Is it possible to run crontab to reboot Android using busybox (or other means)
Tried to run crontab, and it complain about unknown uid 0.
Tried to run reboot, and it does nothing.
Or I am asking for the impossible right now?
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It is a wildcard for every part of the cron schedule expression. So * * * * * means every minute of every hour of every day of every month and every day of the week .
A cron job is a command run by the cron daemon at regularly scheduled intervals. To submit a cron job, specify the crontab command with the -e flag. The crontab command invokes an editing session that allows you to create a crontab file. You create entries for each cron job in this file.
Generally, the most used method to add or modify crontab jobs is the crontab -e command. Run this command in the terminal: This will open a text editor such as nano with the contents of your crontab file. Each crontab job resides on one line, and you may add, modify and remove lines as desired.
Crontab is the answer. Take advantage of the crontab Linux command to automate various mundane and repetitive tasks, simplifying your life. This excellent and easy to use tool, combined with some scripting, can not only automate all sorts of tasks, but also help avoid simple human errors or forgetfulness.
Here are some basic terminal commands you will use to view and modify the crontab file: crontab-l --- List all crontab jobs. crontab -e --- Edit the crontab file. crontab -r --- Remove all entries from the crontab file.
Crontab stands for “cron table, ” because it uses the job scheduler cron to execute tasks; cron itself is named after “chronos, ” the Greek word for time. cron is the system process which will automatically perform tasks for you according to a set schedule.
Requirements
Root access: for superuser commads like reboot, or init.d config. Crond can still run under normal user privs.
Busybox: for 'crond' service
(Optional) init.d support: to start 'crond' service at boot. Or start via Magisk post-fs-data.d script.
Creating cronjob
Create the cronjob file in directory /data/crontab/ (it could be any accessible directory even in sdcard) with filename 'root'. Write your cronjob inside the file 'root'.
echo ' 53 * * * * reboot' >> /data/crontab/root Test without rebooting
Now open any terminal emulator in device and run the following commands..
su - crond -b -c /data/crontab Now the crond service will start, to check type pgrep -l crond or ps | grep crond
Start crond at boot
create a file at /system/etc/init.d with executable permission:
echo ' crond -b -c /data/crontab' > /system/etc/init.d/crond chmod +x /system/etc/init.d/crond Example cronjobs
53 * * * * reboot
Will reboot your device on 53rd minute of every hour.
Note: 1. If you modify crontab, remember to restart crond daemon after killing the existing one.
If the crond is not obeying your timezone, you might need to update the tzdata in your device.
Better to test with */1 * * * * to see if it is working.
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This is a complement to Seff's answer above. Couldn't place it in a comment because it's too long
/system/etc/init.d is not always guaranteed to work. In my case it did not. There are other methods mentioned in the following link in case this one didn't work for you https://android.stackexchange.com/questions/6558/how-can-i-run-a-script-on-boot/196785
Even then crond didn't run any job for me. To debug the errors I killed the running instance pkill crond and ran it like that
crond -f -d0 -c /data/crontab/ This make crond run in forground and print all the debugging information. When I ran it like that I got this warning
crond: crond (busybox 1.27.2-Stericson) started, log level 0 crond: ignoring file 'root' (no such user) So I had to create a passwd file with entry for root
echo 'root:x:0:0:root:/data:/system/bin/sh' > /system/etc/passwd Even then, it still failed with error like
crond: job: 0 /system/bin/ls crond: child running /bin/sh crond: can't execute '/bin/sh' for user root Please note that no where in my cronjob did I mentioned "/bin/sh". This seems to be hard coded in the binary.
Next I added the following lines to my init script
/system/xbin/mount -o remount,rw / /system/xbin/ln -s /system/bin/ /bin /system/xbin/mount -o remount,ro / and that's it. It worked fine after that
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