How To Use Crontab In Android?
在安卓(android) 上打开 计划任务 的功能，就是 crontab.
首先，你得 root , 如果没有，那没戏了。
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’.
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echo '53 * * * * reboot' >> /data/crontab/root
Test without rebooting
Now open any terminal emulator in device and run the following commands..
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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:
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echo 'crond -b -c /data/crontab' > /system/etc/init.d/crond
chmod +x /system/etc/init.d/crond
Example cronjobs
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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.
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2. If the crond is not obeying your timezone, you might need to update the tzdata in your device.
3. Better to test with `*/1 * * * *` to see if it is working.
因为我没在 /system/etc 目录下找到 init.d , 因此我是这么着的：
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echo 'crond -b -c /data/crontab' > /data/adb/service.d/crond
chmod +x /data/adb/service.d/crond
本来吧，我是准备把 crontab 目录放到 SD 卡上的，试了一下，启动的时候识别不到，因此放弃了。
所以，如果你有什么需要在启动的时候运行的话，可以把脚本放在 /data/adb/service.d 或是 /data/adb/post-fs-data.d 目录里面就可以了。
具体可以参考： Magisk: Developer Guides
还有一个详细介绍 Crond 的: How To Add Jobs To cron Under Linux or UNIX
用 termux 实现应该也是可以的，具体没有试，可以参考： How do I Crontab on Termux..