Under GPLv2, it is acceptable and advisable for your offer for source code

to include an Internet link for downloadable source \emph{in addition} to

offering source on a physical medium.  This practice enables those with

fast network connections to get the source more quickly, and typically

decreases the number of physical media fulfillment requests.

(GPLv3~\S~6(b) permits provision of source with a public

network-accessible distribution only and no physical media.  We discuss

this in detail at the end of this section.)

The following is a suggested compliant offer for source under GPLv2 (and

is also acceptable for GPLv3) that you would include in your printed

materials accompanying each binary distribution:

\begin{quote}

The software included in this product contains copyrighted software that

is licensed under the GPL\@.  A copy of that license is included in this

document on page $X$\@.  You may obtain the complete Corresponding Source

code from us for a period of three years after our last shipment of this

product, which will be no earlier than 2011-08-01, by sending a money

order or check for \$5 to: \\

GPL Compliance Division \\

Our Company \\

Any Town, US 99999 \\

\\

Please write ``source for product $Y$'' in the memo line of your

payment.

You may also find a copy of the source at

\verb0http://www.example.com/sources/Y/0.

This offer is valid to anyone in receipt of this information.

\end{quote}

There are a few important details about this offer.  First, it requires a

copying fee.  GPLv2 permits ``a charge no more than your cost of

physically performing source distribution''.  This fee must be reasonable.

If your cost of copying and mailing a CD is more than around \$10, you

should perhaps find a cheaper CD stock and shipment method.  It is simply

not in your interest to try to overcharge the community.  Abuse of this

provision in order to make a for-profit enterprise of source code

provision will likely trigger enforcement action.

Second, note that the last line makes the offer valid to anyone who

requests the source.  This is because v2~\S~3(b) requires that offers be

``to give any third party'' a copy of the Corresponding Source.  GPLv3 has

a similar requirement, stating that an offer must be valid for ``anyone

who possesses the object code''.  These requirements indicated in

pass these offers along with their distributions.  Therefore, the offers

must be valid not only to your customers, but also to anyone who received

a copy of the binaries from them.  Many distributors overlook this

requirement and assume that they are only required to fulfill a request

from their direct customers.

The option to provide an offer for source rather than direct source

distribution is a special benefit to companies equipped to handle a

fulfillment process.  GPLv2~\S~3(c) and GPLv3~\S~6(c) avoid burdening

noncommercial, occasional redistributors with fulfillment request

obligations by allowing them to pass along the offer for source as they

received it.

Note that commercial redistributors cannot avail themselves of the option

(c) exception, and so while your offer for source must be good to anyone

who receives the offer (under v2) or the object code (under v3), it

\emph{cannot} extinguish the obligations of anyone who commercially

redistributes your product.  The license terms apply to anyone who

distributes GPL'd software, regardless of whether they are the original

distributor.  Take the example of Vendor $V$, who develops a software

platform from GPL'd sources for use in embedded devices.  Manufacturer $M$

contracts with $V$ to install the software as firmware in $M$'s device.

$V$ provides the software to $M$, along with a compliant offer for source.

In this situation, $M$ cannot simply pass $V$'s offer for source along to

its customers.  $M$ also distributes the GPL'd software commercially, so

$M$ too must comply with the GPL and provide source (or $M$'s \emph{own}

offer for source) to $M$'s customers.

This situation illustrates that the offer for source is often a poor

choice for products that your customers will likely redistribute.  If you

include the source itself with the products, then your distribution to

your customers is compliant, and their (unmodified) distribution to their

customers is likewise compliant, because both include source.  If you

include only an offer for source, your distribution is compliant but your

customer's distribution does not ``inherit'' that compliance, because they

have not made their own offer to accompany their distribution.

The terms related to the offer for source are quite different if you

distribute under GPLv3.  Under v3, you may make source available only over

a network server, as long as it is available to the general public and

remains active for three years from the last distribution of your product

or related spare part.  Accordingly, you may satisfy your fulfillment

obligations via Internet-only distribution.  This makes the ``offer for

source'' option less troublesome for v3-only distributions, easing

compliance for commercial redistributors.  However, before you switch to a

purely Internet-based fulfillment process, you must first confirm that you

can actually distribute \emph{all} of the software under GPLv3.  Some

programs are indeed licensed under ``GPLv2, \emph{or any later version}''