Differences

This shows you the differences between two versions of the page.

--- linux_wiki:cron [2017/09/03 18:00]
billdozor [Automation Example]
+++ linux_wiki:cron [2019/05/25 23:50]
@@ Line 1: / Line 1: @@
-====== Cron ======
-**General Information**
-Automating tasks with cron (the daemon that executes scheduled commands).
-**Checklist**
-  * Distro(s): Any
-----
-====== User Crontabs ======
-Individual users can create/edit their own cron jobs.
-\\
-List your user's crontab jobs
-<code bash>
-crontab -l
-</code>
-\\
-Edit your crontab
-<code bash>
-crontab -e
-</code>
-\\
-User crontabs are stored at:
-  * /var/spool/cron/<username>
-===== Files That Control Crontab Access =====
-  * /etc/cron.allow
-  * /etc/cron.deny
-About these files:
-  * One username per line
-  * Root can always use crontab, regardless of file existence below
-^  cron.allow  ^  cron.deny  ^  Result  ^
-|  file exists  |  file exists  |  Only users in cron.allow are allowed  |
-|  no file  |  file exists  |  All users allowed except those in cron.deny  |
-|  file exists  |  no file  |  Only users in cron.allow are allowed  |
-|  no file  |  no file  |  Only root is allowed to use crontab  |
-----
-===== Format of User Crontabs =====
-For any below, asterisk means all values.
-<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
-# |  |  |  |  |
-# *  *  *  *  *  command to be executed
-</code>
-----
-===== Crontab Examples =====
-Executes script.sh at 0600,0630,1200,and 1230 every day of the month, every month, and everyday of the week.
-<code bash>
-,30 6,12 * * * /home/user/script.sh
-</code>
-Executes script.sh every minute.
-<code bash>
-* * * * * /home/user/script.sh
-</code>
-Executes script.sh every 5 minutes.
-<code bash>
-*/5 * * * * /home/user/script.sh
-</code>
-Executes script.sh on system startup.
-<code bash>
-@reboot /home/user/script.sh
-</code>
-----
-====== System Cron Jobs ======
-To run jobs in the system directories, look to /etc.
-  * /etc/cron.d/ = system executed jobs (format like crontab)
-  * /etc/cron.daily/ = daily executed scripts (format bash script)
-  * /etc/cron.hourly/ = hourly executed scripts (format bash script)
-  * /etc/cron.monthly/ = monthly executed scripts (format bash script)
-  * /etc/cron.weekly/ = weekly executed scripts (format bash script)
-  * /etc/crontab = system wide crontab
-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**.
-For example, /etc/cron.d/crashplan-mirror:
-<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
-2,14 * * * root /root/scripts/rsync_cp_mirror.sh
-</code>
-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_job)<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
-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>
-----