Licen­ses for most softwa­re and other prac­ti­cal works are desi­gned to take away your fre­edom to sha­re and chan­ge the works. By con­trast, the GNU Gene­ral Public Licen­se is inten­ded to guaran­tee your fre­edom to sha­re and chan­ge all ver­sions of a program–to make sure it rema­ins free softwa­re for all its users. We, the Free Softwa­re Foun­da­tion, use the GNU Gene­ral Public Licen­se for most of our softwa­re; it applies also to any other work rele­ased this way by its authors. You can apply it to your pro­grams, too. When we spe­ak of free softwa­re, we are refer­ring to fre­edom, not pri­ce. Our Gene­ral Public Licen­ses are desi­gned to make sure that you have the fre­edom to distri­bu­te copies of free softwa­re (and char­ge for them if you wish), that you rece­ive sour­ce code or can get it if you want it, that you can chan­ge the softwa­re or use pie­ces of it in new free pro­grams, and that you know you can do the­se things.

To pro­tect your rights, we need to pre­vent others from deny­ing you the­se rights or asking you to sur­ren­der the rights. The­re­fo­re, you have cer­ta­in respon­si­bi­li­ties if you distri­bu­te copies of the softwa­re, or if you modi­fy it: respon­si­bi­li­ties to respect the fre­edom of others.

For exam­ple, if you distri­bu­te copies of such a pro­gram, whe­ther gra­tis or for a fee, you must pass on to the reci­pients the same fre­edoms that you rece­ived. You must make sure that they, too, rece­ive or can get the sour­ce code. And you must show them the­se terms so they know the­ir rights.

Deve­lo­pers that use the GNU GPL pro­tect your rights with two steps: (1) assert copy­ri­ght on the softwa­re, and (2) offer you this Licen­se giving you legal per­mis­sion to copy, distri­bu­te and/or modi­fy it.

For the deve­lo­pers’ and authors’ pro­tec­tion, the GPL cle­ar­ly expla­ins that the­re is no war­ran­ty for this free softwa­re. For both users’ and authors’ sake, the GPL requ­ires that modi­fied ver­sions be mar­ked as chan­ged, so that the­ir pro­blems will not be attri­bu­ted erro­ne­ously to authors of pre­vio­us versions.

Some devi­ces are desi­gned to deny users access to install or run modi­fied ver­sions of the softwa­re insi­de them, altho­ugh the manu­fac­tu­rer can do so. This is fun­da­men­tal­ly incom­pa­ti­ble with the aim of pro­tec­ting users’ fre­edom to chan­ge the softwa­re. The sys­te­ma­tic pat­tern of such abu­se occurs in the area of pro­ducts for indi­vi­du­als to use, which is pre­ci­se­ly whe­re it is most unac­cep­ta­ble. The­re­fo­re, we have desi­gned this ver­sion of the GPL to pro­hi­bit the prac­ti­ce for tho­se pro­ducts. If such pro­blems ari­se sub­stan­tial­ly in other doma­ins, we stand ready to extend this pro­vi­sion to tho­se doma­ins in futu­re ver­sions of the GPL, as needed to pro­tect the fre­edom of users.

Final­ly, eve­ry pro­gram is thre­ate­ned con­stan­tly by softwa­re patents. Sta­tes sho­uld not allow patents to restrict deve­lop­ment and use of softwa­re on gene­ral-pur­po­se com­pu­ters, but in tho­se that do, we wish to avo­id the spe­cial dan­ger that patents applied to a free pro­gram could make it effec­ti­ve­ly pro­prie­ta­ry. To pre­vent this, the GPL assu­res that patents can­not be used to ren­der the pro­gram non-free.

The pre­ci­se terms and con­di­tions for copy­ing, distri­bu­tion and modi­fi­ca­tion follow.