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====== BASH - Directories - Monitor a directory for changes - Using incron ======

**incron** is like cron but instead of time-based events, the events are based on file notifications.

----

===== Install incron =====

<code bash>
sudo apt install incron
</code>


----

===== Change Permissions =====

Add users to the **/etc/incron.allow** file who are allowed to use incron.

<file bash /etc/incron.allow>
peter
</file>

<WRAP info>
**NOTE:**  One user per line.

**/etc/incron.deny** can also be used to specifically prevent usage of incron by a user.
</WRAP>

----

===== Monitor =====

Edit the incron table:

<code bash>
incrontab -e
</code>

and populate with:

<code>
/etc/apache2/apache2.conf IN_MODIFY /usr/sbin/service apache2 stop

/home/peter/some_dir_to_watch IN_MODIFY echo "$$ $@ $# $% $&"
</code>

<WRAP info>
**NOTE:**  This monitors the directory for changes and will perform the echo passing along some parameters.

The format is very picky; use spaces, not tabs!

  * The format is **path mask command**.

Parameters can include:

  * **$$**:  Prints a dollar sign.
  * **$@**:  The watched filesystem path.
  * **$#**:  The event-related file name.
  * **$%**:  The event flags/time (textually).
  * **$&**:  The event flags.time (numerically).


Events to monitor include:

  * **IN_ACCESS**:  If a file is accessed or read.
  * **IN_ATTRIB**:  If metadata of a file change (e.g. timestamps, permissions).
  * **IN_CLOSE_WRITE**:  If a file opened for writing is closed.
  * **IN_CLOSE_NOWRITE**:  If a file or directory not opened for writing is closed.
  * **IN_CREATE**:  If a file or directory is created in a watched directory.
  * **IN_DELETE**:  If a file or directory is deleted from a watched directory.
  * **IN_DELETE_SELF**:  If a watched file or directory is deleted (or moved to a different filesystem).
  * **IN_MODIFY**:  If a file was modified.
  * **IN_MOVE_SELF**:  If a watched file or directory is moved within the filesystem.
  * **IN_MOVED_FROM**:  If a file or directory is moved out of the watched directory.
  * **IN_MOVED_TO**:  A file or directory is moved to the watched directory.
  * **IN_OPEN**:  A watched file or directory is opened.

</WRAP>

<WRAP important>
**IMPORTANT:**  incron is not capable of watching sub-directories.

Only files within the path will be monitored.

If sub-directories need to be monitored, they must be given their own entry.

</WRAP>

----

===== List the incron table =====

<code bash>
incrontab -l
</code>