linux_wiki:cron

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linux_wiki:cron [2017/09/03 16:43]
billdozor [Files That Control Access] 		linux_wiki:cron [2019/05/25 23:50] (current)
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 **General Information** **General Information**
  
-Automating tasks with Cron.+Automating tasks with cron (the daemon that executes scheduled commands).
  
 **Checklist** **Checklist**
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 ====== User Crontabs ====== ====== User Crontabs ======
  
 +Individual users can create/edit their own cron jobs.
 +
 +\\
 List your user's crontab jobs List your user's crontab jobs
 <code bash> <code bash>
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 </code> </code>
  
 +\\
 Edit your crontab Edit your crontab
 <code bash> <code bash>
 crontab -e crontab -e
 </code> </code>
 +
 +\\
 +User crontabs are stored at:
 +  * /var/spool/cron/<username>
  
 ===== Files That Control Crontab Access ===== ===== Files That Control Crontab Access =====
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 About these files: About these files:
   * One username per line   * One username per line
-  * Root can always use cron+  * Root can always use crontab, regardless of file existence below
  
 ^  cron.allow  ^  cron.deny  ^  Result  ^ ^  cron.allow  ^  cron.deny  ^  Result  ^
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 |  no file  |  file exists  |  All users allowed except those in cron.deny  | |  no file  |  file exists  |  All users allowed except those in cron.deny  |
 |  file exists  |  no file  |  Only users in cron.allow are allowed  | |  file exists  |  no file  |  Only users in cron.allow are allowed  |
 +|  no file  |  no file  |  Only root is allowed to use crontab  |
  
 ---- ----
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 For any below, asterisk means all values. For any below, asterisk means all values.
 <code bash> <code bash>
-# m = minute (0-59) +# .---------------- minute (0 - 59) 
-# h = hour (0-23) +# |  .------------- hour (0 - 23) 
-# dom = day of month(1-31) +# |  |  .---------- day of month (1 - 31) 
-# mon = month (1-12) +# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ... 
-# dow = day of week (0-7, 0 or 7 is Sunday) +# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat 
-# cmd = command (command or path to script) +# |  |  |  |  | 
- +# *  *  *  *  *  command to be executed
-# m h dom mon dow cmd+
 </code> </code>
  
 ---- ----
  
-====== Examples ======+===== Crontab Examples =====
  
 Executes script.sh at 0600,0630,1200,and 1230 every day of the month, every month, and everyday of the week. Executes script.sh at 0600,0630,1200,and 1230 every day of the month, every month, and everyday of the week.
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 @reboot /home/user/script.sh @reboot /home/user/script.sh
 </code> </code>
- 
-===== Other Cron keywords ===== 
- 
-  * @reboot - Run once at start up. 
-  * @yearly - Run once a year. 
-  * @annually - Same as yearly. 
-  * @monthly - Run once a month. 
-  * @weekly - Run once a week. 
-  * @daily - Run once a day. 
-  * @midnight - Same as daily. 
-  * @hourly - Run once an hour. 
  
 ---- ----
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 It is recommended to drop scripts into one of the /etc/cron.* directories instead of editing the system wide crontab file. It is recommended to drop scripts into one of the /etc/cron.* directories instead of editing the system wide crontab file.
  
-All formats are bash scripts, except for the /etc/cron.d/ directory, which accepts crontab formatted files, with the addition of specifying a username.+All formats are bash scripts, except for the /etc/cron.d/ directory, which accepts crontab formatted files, **with the addition of specifying a username**.
  
 For example, /etc/cron.d/crashplan-mirror: For example, /etc/cron.d/crashplan-mirror:
 <code bash> <code bash>
 +# .---------------- 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
 +
 # Rsync the crashplan backups to another usb drive for redundancy # Rsync the crashplan backups to another usb drive for redundancy
 0 2,14 * * * root /root/scripts/rsync_cp_mirror.sh 0 2,14 * * * root /root/scripts/rsync_cp_mirror.sh
 </code> </code>
 The above executes at 0200 and 1400, runs as the user root, the script specified. The above executes at 0200 and 1400, runs as the user root, the script specified.
 +
 +----
 +
 +====== Cron Keywords ======
 +
 +Keywords that can be used in place of a specific time/date schedule.
 +
 +  * @reboot - Run once at start up.
 +  * @yearly - Run once a year.
 +  * @annually - Same as yearly.
 +  * @monthly - Run once a month.
 +  * @weekly - Run once a week.
 +  * @daily - Run once a day.
 +  * @midnight - Same as daily.
 +  * @hourly - Run once an hour.
 +
 +----
 +
 +====== Cron - Relative Days ======
 +
 +Cron is great at being specific about minutes, hours, dates, months, and days of the week, but is not able to handle relative days.
 +  * Relative days could come in handy when you need a job to execute on something such as the 1st, 2nd and 3rd Tuesday of every month.
 +  * In order to accomplish this, a combination of cron and a date checker script is used.
 +
 +===== Automation Example =====
 +
 +In this example, we want a script to execute on the 1st, 2nd, and 3rd Tuesday of every month, with different arguments depending upon which Tuesday it is.
 +
 +  * Cron entry: Execute a date checker script every Tuesday
 +    * Create the system wide cron entry (/etc/cron.d/automated_jobs)<code bash cron-automated-jobs># .---------------- 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
 +
 +#Every Tuesday at 0800: Determine if an automated job should be run
 +#-Target: 1st,2nd,3rd Tues of month
 +00 08 * * tue  root  /automation/automated-job-check.sh
 +</code>
 +
 +  * Date checker script: Determine if the actual automated program should run and what arguments to send it.
 +    * Create the date checker script (/automation/automated-job-check.sh)<code bash automated-job-check.sh>#!/bin/bash
 +# Title: automated-job-check.sh
 +# Description: Determine if an automated job should be run
 +
 +# Script to execute: See 'if statement' for dynamically selecting an environment
 +script="/automation/scripts/automated-job.py"
 +
 +# Log file
 +log_file="/var/log/automation/automated-job-check_$(date +%Y%m).log"
 +
 +echo "==== Log Started: $(date) ====" >> ${log_file}
 +
 +# If today is Tuesday AND today is >=1 and <=21(1st,2nd,3rd Tue)
 +if [[ "$(date '+%a')" == "Tue" ]] && [[ $(date +%-d) -ge 1 ]]; then
 +
 +  # First Tue: Development Environment
 +  if [[ $(date +%-d) -le 7 ]]; then
 +    echo ">> OK: Today is the first Tue of the Month; execute script(${script} --group all_dev)." >> ${log_file}
 +    ${script} --group all_dev 2>&1 >> ${log_file}
 +
 +  # Second Tue: Test Environment
 +  elif [[ $(date +%-d) -le 14 ]]; then
 +    echo ">> OK: Today is the second Tue of the Month; execute script(${script} --group all_test)." >> ${log_file}
 +    ${script} --group all_test 2>&1 >> ${log_file}
 +
 +  # Third Tue: Production Environment
 +  elif [[ $(date +%-d) -le 21 ]]; then
 +    echo ">> OK: Today is the third Tue of the Month; execute script(${script} --group all_prod)." >> ${log_file}
 +    ${script} --group all_prod 2>&1 >> ${log_file}
 +
 +  else
 +    echo ">> NO-EXEC: Today is NOT the first,second, or third Tue of the Month. Will NOT execute script(${script})." >> ${log_file}
 +  fi
 +else
 +  echo ">> NO-EXEC: Today is NOT the first,second, or third Tue of the Month. Will NOT execute script(${script})." >> ${log_file}
 +fi
 +
 +echo -e "==== Log Ended: $(date) ====\n" >> ${log_file}
 +</code>
 +
 +==== Other Date Check Examples ====
 +
 +A few other examples of date checker scripts with relative days before/after.
 +
 +\\
 +**7 Days before the first Tuesday of the month**<code bash>#!/bin/bash
 +# Title: automated-job-check.sh
 +# Description: Determine if an automated job should be run
 +
 +# Script to execute:
 +script="/automation/scripts/automated-job.py"
 +
 +# Log file
 +log_file="/var/log/automation/automated-job-check_$(date +%Y%m).log"
 +
 +echo "==== Log Started: $(date) ====" >> ${log_file}
 +
 +# If today is Tuesday AND 7 days from now is >=1 and <=7(first Tue)
 +if [[ "$(date '+%a')" == "Tue" ]] && [[ $(date +%-d -d "+7 days") -ge 1 ]]; then
 +  if [[ $(date +%-d -d "+7 days") -le 7 ]]; then
 +    echo ">> OK: Seven days from now is the first Tue of the Month; execute script(${script})." >> ${log_file}
 +    ${script} 2>&1 >> ${log_file}
 +  else
 +    echo ">> NO-EXEC: Seven days from now is NOT the first Tue of the Month. Will NOT execute script(${script})." >> ${log_file}
 +  fi
 +else
 +  echo ">> NO-EXEC: Seven days from now is NOT the first Tue of the Month. Will NOT execute script(${script})." >> ${log_file}
 +fi
 +
 +echo -e "==== Log Ended: $(date) ====\n" >> ${log_file}
 +</code>
 +
 +\\
 +**2 Days after the third Tuesday of the month**<code bash>#!/bin/bash
 +# Title: automated-job-check.sh
 +# Description: Determine if an automated job should be run
 +
 +# Script to execute
 +script="/automation/scripts/automated-job.py"
 +
 +# Log file
 +log_file="/var/log/automation/automated-job-check_$(date +%Y%m).log"
 +
 +echo "==== Log Started: $(date) ====" >> ${log_file}
 +
 +# If today is Thursday AND two days ago was >=15 and <=21(third Tue)
 +if [[ "$(date '+%a')" == "Thu" ]] && [[ $(date +%-d -d "-2 days") -ge 15 ]]; then
 +  if [[ $(date +%-d -d "-2 days") -le 21 ]]; then
 +    echo ">> OK: Two days ago was the third Tue of the Month; execute script(${script})." >> ${log_file}
 +    ${script} 2>&1 >> ${log_file}
 +  else
 +    echo ">> NO-EXEC: Two days ago was NOT the third Tue of the Month. Will NOT execute script(${script})." >> ${log_file}
 +  fi
 +else
 +  echo ">> NO-EXEC: Two days ago was NOT the third Tue of the Month. Will NOT execute script(${script})." >> ${log_file}
 +fi
 +
 +echo -e "==== Log Ended: $(date) ====\n" >> ${log_file}
 +</code>
 +
 +----
 +
  • linux_wiki/cron.1504471429.txt.gz
  • Last modified: 2019/05/25 23:50
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