Create Persistence_Mechanisms.md

Author: NextGenSec-Github

DFIR/Digital Forensics/Linux/Persistence_Mechanisms.md

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+## Cron Jobs (/etc/crontab)
+The /etc/crontab file is a system-wide configuration file used to schedule periodic tasks or jobs on Unix-like operating systems, including Linux. It is part of the cron system, which is a time-based job scheduler in Unix-like operating systems.
+Here's an example of what you might find in an /etc/crontab file:
+
+```bash
+# /etc/crontab: system-wide crontab
+# Unlike any other crontab you don't have to run the `crontab'
+# command to install the new version when you edit this file.
+# This file also has a username field, that none of the other crontabs do.
+
+SHELL=/bin/bash
+PATH=/sbin:/bin:/usr/sbin:/usr/bin
+MAILTO=root
+
+# For details see man 5 crontab
+
+# Example of job definition:
+# .---------------- 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
+17 *    * * *   root    cd / && run-parts --report /etc/cron.hourly
+25 6    * * *   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.daily )
+47 6    * * 7   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly )
+52 6    1 * *   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.monthly )
+```