From SqueezeboxWiki

Modifying files on your Controller

With SqueezeOS you can safely modify any of the files stored on the Controller for prototyping and development. The released firmware is stored in a read-only filesystem in the flash, a writeable overlay filesystem is used that allows modification of any files. You don't need to worry if these modifications stop your Controller from working, a factory reset will erase the overlay filesystem restoring the firmware to the original state.

Starting with the 7.1 firmware all modifications are removed after a firmware upgrade. All settings files are kept, this is currently all files in /etc and all settings.lua files. You can easily reapply your changes using an SD card.

Using an SD card

You can store the system log and any application core files using on an SD card. First create a /log folder using your PC, then put the SD card into your Controller and insert the battery. All log messages will now be written in the /log/messages file. If the application crashes all core files will also be stored in the /log folder for analysis.

Starting with the 7.1 firmware SqueezeOS will also use additional files on your SD card. These are:

squeezeos.patch 

the patch file is automatically applied to the filesystem following a factory reset. This lets you automatically install any local modifications to your Controller. Be warned that after an upgrade the new firmware may conflict with the local changes and prevent the Controller from working correctly. In this case remove the patch file from the SD card and perform a factory reset.

squeezeos-post-reset.sh 

this script is executed after a factory reset and can be used to modify the filesystem or perform custom actions. (In the 7.0 firmware this script was called firstboot.sh).

squeezeos-boot.sh 

this script is exeucted every time the Controller is booted, is can be used to perform custom actions. (In the 7.0 firmware this script was called jiveboot.sh).

squeezeplay 

if you create a squeezeplay directory this is added to the LUA_PATH and can be used to install lua extensions and custom applets on the SD card.

Fast and Easy Screen Captures from the Squeezebox Controller

What you do:

1. Insert an SD card in the Controller and turn it on.
2. Navigate to the screen you want to capture.
3. Simultaneously press and hold the REW and PAUSE buttons for two seconds. A short “tick” sound will confirm that a screen shot has been taken.
4. Repeat this process for whatever screen shots you need.
5. Shut down the SBC and remove the SD card

Now all you need to do is take the SD card out of the Controller and place it in an SD card reader attached to your computer to access the images.