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--- linux_wiki:cron [2017/09/03 16:51]
billdozor [Cron keywords]
+++ linux_wiki:cron [2019/05/25 23:50] (current)
@@ Line 14: / Line 14: @@
 Individual users can create/edit their own cron jobs.
+\\
 List your user's crontab jobs
 <code bash>
@@ Line 19: / Line 20: @@
 </code>
+\\
 Edit your crontab
 <code bash>
 crontab -e
 </code>
+\\
+User crontabs are stored at:
+  * /var/spool/cron/<username>
 ===== Files That Control Crontab Access =====
@@ Line 45: / Line 51: @@
 For any below, asterisk means all values.
 <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>
@@ Line 94: / Line 99: @@
 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:
 <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
@@ Line 117: / Line 130: @@
   * @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
+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>
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