cron: Periodically scheduled task, the task cycling plans, mainly for backing up data.
crontab
Usage: crontab [-u the User] [-e | the -l | -r]
-u <the User> Specifies the user the DEFINE the User #
-e edit user's crontab # edit scheduled tasks
-l list user's crontab # View Scheduled Tasks
-r delete user's crontab # delete a scheduled task
1, crontab -e to edit the contents of a periodic scheduled task
2, view the configuration: cat / etc / crontab
time
min hour day month week command
-minute hour day week month action (task commands)
0-590- 231-311-120-7 command or script (write absolute path)
all the documents 30 2 1 * * rm -rf / tmp / * // delete the number at 2:30 monthly 1 / tmp directory
5 * * 6 3 rm -rf / tmp / * // all files under five minutes to delete three hour a week in June each year the / tmp directory
All files 6 6 * 6 6 rm -rf / tmp / * // 6 minutes at 6:00 deletion Saturday in June each year the / tmp directory
* Any time
- period of time // 8-11 * * * * rm -rf / tmp / * // under 8 minutes 9 minutes 10 minutes 11 minutes per hour of deleted the / tmp directory of all files
, separate (discrete time) All files // 1,2,5,9 * * * * rm -rf / tmp / * // 1 minute 2 minutes 5 minutes 9 minutes per hour of deleted the / tmp directory
0-4,8-12 //
0 -23/2 interval // 1 0-23 / 2 * * * rm -rf / tmp / * // "0,2,4,6,8,10,12,14,16,18,20,22 ").
* / 2 every two hours // 1 * / 2 * * * rm -rf / tmp / * rm command executed every 2 hours
* 0-23 * * * rm -rf /tmp/*
* */1 * * * rm -rf /tmp/*
3, the wording of time
The time and date fields are:
field allowed values
----- --------------
minute 0-59
hour 0-23
day of month 1-31
month 1-12 (or names,
see below)
day of week 0-7 (0 or 7 is
Sun, or use names)
Case I: every Wednesday at 10:00 pm backup / etc / directory to the / tmp directory called 2017-04-12_etc.tar.gz backup file contains today's date
crontab -e
* 22 * 3 * / usr / bin / tar cvzf / tmp / `/ usr / bin / date +% F`_etc.tar.gz / etc
Note:` `the` `command to replace the function of the command, the system first performs` `(trans prime backticks) of command. Can also be written as `` $ ()
Case II: Keep only the last one month of the log file
crontab -e
1 * * * * the Find / var / log -mtime +30 | xarge -i RM -rf {}
Case 3: monthly No. 1 2:30 empty the temporary disk
crontab -e
30 2 1 * * / usr / bin / RM -rf / tmp / *
case four: Every day 8:10 off the computer at night, except Saturdays, Friday Sundays 17:10 Turn off the computer
crontab -e
10 20 * * 1-4 / usr / sbin / poweroff
10 * 17 * 5, 7 / usr / sbin / poweroff
case 5: jim user at home every day to create a directory named after the date directory 20,170,412
the crontab -e -u Jim
. 1 0 * * * / bin / mkdir / Home / Jim / `DATE the Y% +% m% d`
4, periodically query the contents of the scheduled tasks
crontab -l # to view the current user
crontab -u jim - # View the specified user
5, periodically delete all scheduled tasks a user (delete a scheduled task crontab -e to enter text deleted)
crontab -r # current user
crontab -u jim -r # specified user
System-defined scheduled task (default)
updates the whatis database
update updatedb database
log periodic rotation roll (log cutting)
to clean / tmp / var / tmp
state information collection system
vim / etc / crontab configuration file
# For details see man 4 crontabs
Example of the Job Definition #:
# .---------------- minute (0 - 59)
# | .------------- hour (0 - 23 is)
# | | .---------- month The Day of (. 1 - 31 is)
# | | | .------- month The (. 1 - 12 is) OR Jan, On Feb,-Mar, On Apr ...
# | | | | .---- Day of Week (0 -. 6) (or the Sunday = 0. 7) oR Sun, Mon, Tue, Wed, Thu, Fri, SAT
# | | | | |
# * * * * the User-* name the command to BE the executed
* / 5 * * * * root command // every five minutes to execute commands as root
Scripts can exist within the script directory will be in accordance with the following time to execute
cd / etc
cron.hourly / # per hour
cron.weekly / # weekly
cron.daily / # day
cron.monthly / # month
6, unused files deleted more than a month
CAT /etc/cron.daily/tmpwatch
7, crontab Service Management:
Are search software is installed: rpm -q crontabs
list file search software: rpm -ql crontabs
check software configuration files list: rpm -qc crontabs
service status: systemctl status crond Note: d is the daemon daemon
to restart at the service: systemctl restart crond service crond restart or
shut down at service: systemctl stop crond or service crond stop
the boot does not start at the service: systemctl disable crond or chkconfig crond off
the boot at the service: systemctl enable crond crond oN or chkconfig
8, cron rights management
/etc/cron.allow white list: allows only users in this list using crontab (the file itself does not exist)
/ etc / cron.deny blacklist: users in this list can not use crontab
Note: neither file exists, only the root user can use crontab
Two files are present, allow the implementation of priority
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Disclaimer: This article is CSDN blogger "coisini_ Mi" in the original article, follow the CC 4.0 by-sa copyright agreements, please attach a reprint the original source link and this statement.
Original link: https: //blog.csdn.net/qq_34889607/article/details/78635141