Licensing Free software

copyleft, novel use of copyright law ensure works remain unrestricted, originates in world of free software.

all free software licenses must grant users freedoms discussed above. however, unless applications licenses compatible, combining programs mixing source code or directly linking binaries problematic, because of license technicalities. programs indirectly connected may avoid problem.

the majority of free software falls under small set of licenses. popular of these licenses are:

the mit license
the gnu general public license v2
the apache license
the gnu general public license v3
the bsd license
the gnu lesser general public license
the mozilla public license (mpl)
the eclipse public license

the free software foundation , open source initiative both publish lists of licenses find comply own definitions of free software , open-source software respectively:

list of fsf approved software licenses
list of osi approved software licenses

the fsf list not prescriptive: free licenses can exist fsf has not heard about, or considered important enough write about. s possible license free , not in fsf list. osi list lists licenses have been submitted, considered , approved. open-source licenses must meet open source definition in order officially recognized open source software. free software on other hand more informal classification not rely on official recognition. nevertheless, software licensed under licenses not meet free software definition cannot rightly considered free software.

apart these 2 organizations, debian project seen provide useful advice on whether particular licenses comply debian free software guidelines. debian doesn t publish list of approved licenses, judgments have tracked checking software have allowed software archives. summarized @ debian web site.

it rare license announced being in-compliance fsf guidelines not meet open source definition, although reverse not true (for example, nasa open source agreement osi-approved license, non-free according fsf).

there different categories of free software.

public domain software: copyright has expired, work not copyrighted (released without copyright notice before 1988), or author has released software onto public domain waiver statement (in countries possible). since public-domain software lacks copyright protection, may freely incorporated work, whether proprietary or free. fsf recommends cc0 public domain dedication purpose.
permissive licenses, called bsd-style because applied of software distributed bsd operating systems: these licenses known copyfree have no restrictions on distribution. author retains copyright solely disclaim warranty , require proper attribution of modified works, , permits redistribution , modification, closed-source ones. in sense, permissive license provides incentive create non-free software, reducing cost of developing restricted software. since incompatible spirit of software freedom, many people consider permissive licenses less free copyleft licenses.
copyleft licenses, gnu general public license being prominent: author retains copyright , permits redistribution under restriction such redistribution licensed under same license. additions , modifications others must licensed under same copyleft license whenever distributed part of original licensed product. known viral, protective, or reciprocal license. due restriction on distribution not considers type of license free.




^ carver, brian w. (2005-04-05). share , share alike: understanding , enforcing open source , free software licenses . berkeley technology law journal. 20: 39. 
^ top 20 licenses . black duck software. 19 november 2015. retrieved 19 november 2015. 1. mit license 24%, 2. gnu general public license (gpl) 2.0 23%, 3. apache license 16%, 4. gnu general public license (gpl) 3.0 9%, 5. bsd license 2.0 (3-clause, new or revised) license 6%, 6. gnu lesser general public license (lgpl) 2.1 5%, 7. artistic license (perl) 4%, 8. gnu lesser general public license (lgpl) 3.0 2%, 9. microsoft public license 2%, 10. eclipse public license (epl) 2% 
^ balter, ben (2015-03-09). open source license usage on github.com . github.com. retrieved 2015-11-21. 1 mit 44.69%, 2 other 15.68%, 3 gplv2 12.96%, 4 apache 11.19%, 5 gplv3 8.88%, 6 bsd 3-clause 4.53%, 7 unlicense 1.87%, 8 bsd 2-clause 1.70%, 9 lgplv3 1.30%, 10 agplv3 1.05% 
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^ various licenses , comments them . gnu.org. retrieved 20 march 2014. 
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