"Run a command if the folder changes" container


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Edit Jun26: Updated for the new USER_ID, GROUP_ID, and UMASK config settings.

 

Hi all,

 

I've created a container that uses inotify to watch a directory for changes, then invoke a user-specified command.

 

Documentation is here: https://registry.hub.docker.com/u/coppit/inotify-command/

 

The easiest way to use it is to paste this URL into your template repositories, then use the template when creating a new container: https://github.com/coppit/docker-templates

 

You create a config file for each dir/command pair. There are lots of ways to use this. Here's an example:

 

newperms.conf, for running newperms whenever there's a change in the cache directory:

 

WATCH_DIR=/dir2
SETTLE_DURATION=5
MAX_WAIT_TIME=30
MIN_PERIOD=30
COMMAND="/root/newperms /dir2"
USER_ID=0
GROUP_ID=0
UMASK=0000
# This is important because chmod/chown will change files in the monitored directory
IGNORE_EVENTS_WHILE_COMMAND_IS_RUNNING=1

 

sagetv.conf, for telling SageTV to rescan its imported media when the media directory changes:

 

WATCH_DIR=/dir1
SETTLE_DURATION=5
MAX_WAIT_TIME=05:00
MIN_PERIOD=10:00
COMMAND="wget -nv -O /dev/null --auth-no-challenge http://sage:frey@192.168.1.102:8080/sagex/api?c=RunLibraryImportScan&1="
USER_ID=0
GROUP_ID=0
UMASK=0000
# This is not important because the above is a "fire and forget" asynchronous operation
IGNORE_EVENTS_WHILE_COMMAND_IS_RUNNING=0

 

Then I create a container that maps the proper directories for /dir1 and /dir2, and also the newperms utility:

 

docker run --name=inotify-command -d -v /etc/localtime:/etc/localtime \
  -v /mnt/vms/docker-config/inotify-command:/config:rw \
  -v /mnt/user/Media:/dir1 -v /mnt/cache:/dir2:rw \
  -v /usr/local/sbin/newperms:/root/newperms coppit/inotify-command

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Question:  if im writing a file does it execute the script when the file starts writing or when its finished?

 

Excellent question. It triggers when the file is closed in write mode, not when it's created, read, or written. inotify is a bit funky. For example, it also triggers for new directories, for the case where someone copies a directory containing a ton of files into the watch dir.

 

I thought about allowing the user to customize the events, but given how funky inotify is, I figured that would be too complicated for most users.

 

Note that this doesn't prevent your command from stomping all over a file that's being written, after being triggered by another file that was write-closed. So, for example, you wouldn't want a command that moves files out of the watch dir blindly -- it would need to use lsof or something to determine which are safe to move.

 

Here's the full list of file events:

 

ATTRIB

CLOSE_WRITE,CLOSE

MOVED_TO

MOVED_FROM

DELETE

 

And dir events:

 

ATTRIB,ISDIR

CREATE,ISDIR

MOVED_TO,IS_DIR

MOVED_FROM,IS_DIR

DELETE,ISDIR

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  • 3 years later...

Moved to Alpine linux, reducing the image size from 232MB to 90MB

 

Also:

  • Make the change monitors more like services that restart if they crash.
  • Added a feature to use polling, so that Windows shares can be monitored too.
Edited by coppit
Mention polling feature.
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I added the inotify-command docker and set the host path to point at the directory I want to monitor.  The docker never starts and nothing is showing up in the sytem log to explain why.  I didnt modify either Key 1 or Key 2.

 

Edit: And Im an idiot, RTFM.  I thought I had to get it up and running so I could access its console to modify sample.conf, nope.  I have it up and running but now need to install comskip.  Any chance of cloning this into a repo that automatically installs comskip?

Edited by Ryland
RTFM
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  • 5 months later...
  • 1 year later...

It would be great if we could tweak what functions we would want to use (or not use). Maybe via container variables?

 

For example, I have a 'dropbox' style file upload app that I use that doesn't require authentication to upload files and deletes them automatically when retention timer is up. It's dead simple and I like it that way. But I want to watch for files getting created(uploaded) in that directory and not at all if those files are deleted. 

 

So would be great to be able to exclude DELETE,ISDIR for example

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