cronjob doc

CronJob/CronJob.md

@@ -0,0 +1,40 @@
+```txt
+ .---------------- 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
+```
+Here are some examples to illustrate different cron job schedules:
+
+### Example 1: Run at 12:55 every day
+```
+55 12 * * * root hi
+```
+This command runs `hi` as the `root` user every day at 12:55.
+
+### Example 2: Run every minute
+```
+*/1 * * * * root hi
+```
+This command runs `hi` as the `root` user every minute.
+
+### Example 3: Run every 2 minutes
+```
+*/2 * * * * root hi
+```
+This command runs `hi` as the `root` user every 2 minutes.
+
+### Example 4: Run at specific minutes
+``` 
+10,20,30 10 * * * root hi
+```
+This command runs `hi` as the `root` user at 10:10, 10:20, and 10:30.
+
+### Example 5: Run after every reboot
+```
+@reboot root hi
+```
+This command runs `hi` as the `root` user after system reboot.