Snapcraft Layout bind-file results in an empty file at the specified location

snapcraft
#1

Hello,

I’m trying to understand how the Layout is supposed to function. My ultimate goal is to make available a configuration file within $SNAP_DATA that a utility (one of two apps in my snapcraft.yaml) could then modify when called by a snap set command (from the outside world).

My currently configured Layouts work as expected for files and directories that I need to be in place in $SNAP_DATA during the snap build process; the main app launches and writes to them.

My Layout for the configuration file though, also works in that the bind-file results in the file being in the location specified by the Layout within $SNAP_DATA, but the file is empty (0 bytes).

I’ve read different posts about migrating a configuration file over from /etc, /home, $SNAP etc using an install-hook and/or configure-hook, but nothing has worked for me. What is the best practice to achieve this? A few posts explain away without the use of a Layout but I can’t tell if that’s only because the post preceded the intro of Layouts, or not. Thx in advance!

#2

It would help if you could share your snapcraft.yaml and the code you used for the install hook

#3

Hi @ogra,

I was able to achieve my interim step of getting a writable copy of my conf.json file deposited into $SNAP_DATA by using an install-hook and not a Layout nor configure-hook.

Here’s the install-hook that worked for me.

#!/bin/sh -e

Copy conf.json file to $SNAP_DATA

validate the file’s existence

if [ ! -f $SNAP/conf/conf.json ] ; then echo “ERROR: The file does NOT exist” exit 1 fi

If it exists, copy conf.json from $SNAP to $SNAP_DATA

mkdir -m 755 $SNAP_DATA/edge/conf cp $SNAP/conf/conf.json $SNAP_DATA/edge/conf

But I still have the question from my post → I had thought I could achieve this same result via bind-file Layout but it resulted in an empty file instead. For my own understanding, why would that happen?

This is a snippet of that Layout:

$SNAP/conf/conf.json bind-file: $SNAP_DATA/edge/conf/conf.json

This was the resulting empty file at the correct location:

user@ubuntu-server01:/var/snap/edgenoplugins/current/edge/conf$ ls -ltr total 0 -rwxr-xr-x 1 root root 0 Nov 7 15:52 conf.json

Thanks!