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cron 은 주기적으로 특정 작업을 스케쥴링하기 위해 리눅스에세 제공해 주는 명령으로

contab 을 통해 작업들을 설정한다.

editor 설정

crontab -e 실행시 select-editor 명령이 호출되어 editor 설정된다.

editor를 바꾸고 싶을때는 select-editor 를 실행 하거나 ~/.selected_editor 의 SELECTED_EDITOR 의 값을 바꾼다.

select-editor 명령 실행시 원하는 editor가 없을 경우에는 SELECTED_EDITOR 값을 변경하자.

crontab -e 명령을 실행하면 다음과 같은 형식으로 값을 사용하면 된다.

m h  dom mon dow   command

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)

(Manual page crontab(5))

사용 예는 다음과 같다

The following lists an example of a user crontab file.    
    
# use /bin/bash to run commands, instead of the default /bin/sh    
SHELL=/bin/bash    
# mail any output to `paul', no matter whose crontab this is    
MAILTO=paul    
#    
# run five minutes after midnight, every day    
5 0 * * *       $HOME/bin/daily.job >> $HOME/tmp/out 2>&1    
# run at 2:15pm on the first of every month — output mailed to paul    
15 14 1 * *     $HOME/bin/monthly    
# run at 10 pm on weekdays, annoy Joe    
0 22 * * 1-5    mail -s "It's 10pm" joe%Joe,%%Where are your kids?%    
23 0-23/2 * * * echo "run 23 minutes after midn, 2am, 4am ..., everyday"    
5 4 * * sun     echo "run at 5 after 4 every Sunday"    
0 */4 1 * mon   echo "run every 4th hour on the 1st and on every Monday"    
0 0 */2 * sun   echo "run at midn on every Sunday that's an uneven date"    
# Run on every second Saturday of the month    
0 4 8-14 * *    test $(date +\%u) -eq 6 && echo "2nd Saturday"    
    
All the above examples run non-interactive programs.  If you wish to run a program that interacts with  the    
user's desktop you have to make sure the proper environment variable DISPLAY is set.    
    
# Execute a program and run a notification every day at 10:00 am    
0 10 * * *  $HOME/bin/program | DISPLAY=:0 notify-send "Program run" "$(cat)"

(Manual page crontab(5))

예약어도 사용할수 있다

string         meaning
------         -------
@reboot        Run once, at startup.
@yearly        Run once a year, "0 0 1 1 *".
@annually      (same as @yearly)
@monthly       Run once a month, "0 0 1 * *".
@weekly        Run once a week, "0 0 * * 0".
@daily         Run once a day, "0 0 * * *".
@midnight      (same as @daily)
@hourly        Run once an hour, "0 * * * *".

(Manual page crontab(5))