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Replacing incron with adhocify and systemd

 Publish date: Sep 16, 2023 • Last updated: Sep 17, 2023

Introduction

In one of our businesses, we process a lot of inbound EDI and EDI-like data. We like to process those inbound data in real-time and to do so we use Linux’s inotify facilities and have primarily done so via incron . However, incron appears to be abandonware and we keep stumbling upon irritating bugs with it. And so, in September of 2023, I tried to find a solid replacement for incron that did not change the paradigm that we have in place and that we like.

I honestly expected to find a modern incron replacement, but it appears that no such thing exists. I evaluated many solutions posed by a number of people that Google turned up, but I didn’t like any of them. And so, I designed a solution that works well for us and that solution is described in this article.

In brief, we replaced the entries within our /etc/incron.d/* files with systemd service units that utilize adhocify .

An Example Incron Configuration

This is an example of the type of entries that we have had incron manage that we replaced with adhocify within systemd service units:

$ cat /etc/incron.d/example
/home/customer/events_from_vendor IN_CLOSE_WRITE,recursive=false,loopable=true /usr/local/bin/process_customer_events_from_vendor.sh $@/$#

Adhocify Replacement Configuration

This is a systemd service unit config file to replace the entry shown above:

$ cat /etc/systemd/system/adhocify-customer_events_from_vendor.service
[Unit]
Description=Adhocify-led Processing of Customer Events from Vendor
After=network.target

[Service]
ExecStart=/usr/local/bin/adhocify --mask IN_CLOSE_WRITE --path /home/customer/events_from_vendor /usr/local/bin/process_customer_events_from_vendor.sh {}
KillMode=control-group
Restart=always
RestartSec=10s
Type=simple

[Install]
WantedBy=multi-user.target

Notes / Wrap-up

  1. Be sure to remove /etc/incron.d/<foo> entries and restart incron prior to enabling the adhocify+systemd unit replacement.
  2. The adhocify-customer_events_from_vendor.service will need to be enabled and started via systemctl, which is outside the scope of this article.
  3. One nice side effect of this solution is that standard output from all of the processing is logged to the systemd unit, and so, “systemctl status <service>" will show the status and most recent logs and “journalctl –no-pager -u <service>" will show all of the logs.
  4. I built adhocify v1.1 myself, by simply running make in the source tree, and then I copied the binary into /usr/local/bin/.
  5. I do not know if this solution can replace all incron use cases, but it nicely covers ours.

Postscript

Not long after implementing the solution described in this article, I discovered the official GNU project named direvent, which seems like a great and cross-platform incron replacement that would work well for our use cases. Had I found direvent first, this blog post likely would have not ever been written. https://www.gnu.org.ua/software/direvent/