As far the GPLv3 is concerned you must include the "installation information" necessary to modify and reinstall the software (GPLv3 Sec. 6). For instance you must provide link and perhaps some instructions needed to acquire the verbatim source code for the software running on your device.
For yourself it sounds like it's best you provide a disclaimer such as "This product uses the GNU/Debian <version> operating system, source code and installation of Debian can be found at www.debian.org." You should also provide a list or a link to a list that shows what all packages are being used and where to find them.
Note that each package can differ in license; some packages may use GPLv3, GPLv2, LGPL, MIT, Apache, WTFPL, etc. Point given that some packages do not even need their source code conveyed.
On February 22, 2017 at 9:29 AM kevin anthoney <kevin.anthoney@weldspares.co.uk> wrote:We're looking at developing a commercial product, which will essentially be a PC running Debian with a browser on it configured to connect to our web app.Would we need to provide source code for all the GPL software running on the PC? Assuming the answer is "yes", is there a sensible method of collating all the necessary source code?