Linux Task Scheduler Cron

Cat/etc/crontab//configuration file for Task Scheduler
Shell=/bin/bash//define Shell variables
Path=/sbin:/bin:/usr/sbin:/usr/bin//Environment variables
Mailto=root//mailto Send mail to WHO

#For details see Mans 4 Crontabs

#Example of Job Definition:
.----------------minute (0-59)///The following five * * * * represent 5 bits, the first bit is the minute, the range is 0-59
#|.-------------Hour (0-23)//second bit is hour, range 0-23
#| |.----------Day of Month (1-31)//Third bit is date, range 1-31
#| | |.-------month (1-12) or jan,feb,mar,apr ...//fourth digit is month, range 1-12, numeric and English shorthand
#| | | |.----DAY of Week (0-6) (sunday=0 or 7) or Sun,mon,tue,wed,thu,fri,sat//fifth is week, 0 or 7 means Sunday, can also be written in English shorthand
#| | | | |
# user-name command to be executed//uesr-name default Root,command to be executed is required to execute
#crontab-E//Enter the crontab configuration file, using the same method as Vim, press I to enter edit mode

Instance:
There is a task schedule: 3 o'clock in the morning every day to execute the/usr/local/sbin/123.sh script, and the correct and incorrect logs are appended to the/tmp/123.log file, the specific command is as follows:
0 3 /bin/bash/usr/local/sbin/123.sh >>/tmp/123.log 2>>/tmp/123.log
Note: denotes all meaning, the first indicates that each month's 1-31 number is executed, the second represents 1-12 months each year is executed, the third * represents every day of the week is executed, the format is: minutes + hours + days + months + weeks + specific commands

0 3 1-10 /2 /bin/bash/usr/local/sbin/123.sh >>/tmp/123.log 2>>/tmp/123.log
Note: Every year two months of 1-10 go to execute the/usr/local/sbin/123.sh script and append both the correct and the wrong log to the/tmp/123.log file

0 3 1-10 */2 2,5/bin/bash/usr/local/sbin/123.sh >>/tmp/123.log 2>>/tmp/123.log
Note: 2,5 says that as long as Tuesday and Friday go to execute
#systemctl start Crond//write a task plan cron and use the command to start the Crond service.
#ps-aux |grep cron//Check cron service has no boot

To resolve a well-written scheduled task that does not perform the method:
Either write the absolute path or write your own command to the PATH environment variable in/etc/crontab, but the surest way is to write the absolute path
Recommendation: Each write a task plan, to append the correct log and error log, so as to be able to be documented, do not perform a task scheduled to view the task execution log can be wrong

[Email protected] ~]# crontab-l
No crontab for Root
[Email protected] ~]# CRONTAB-E
Enter the following line in the task plan:
1 2 /usr/bin/find/tmp/-type f-mtime +100 |xargs rm-f//means find and delete files with/tmp/for more than 100 days
No crontab for root-using an empty one
Crontab:installing New Crontab
[[email protected] ~]# crontab-l//Use this command to view the task schedule you just added
1 2 /usr/bin/find/tmp/-type f-mtime +100 |xargs rm-f

Crontab file location path/var/spool/cron/This will have the user's cron, such as viewing the root user cron,
#cat/var/spool/cron/root
1 2 /usr/bin/find/tmp/-type f-mtime +100 |xargs rm-f//Check the result is the cron of the root user

#crontab-E//Edit task Schedule
#crontab-L//List task schedule
#crontab-r//Delete task schedule
#crontab-U root-l//Use-u to specify a user

Linux Task Scheduler Cron