"The OpenSSL license, which is BSD-style with an advertising
clause, has been a source of problems in the past because it is
rather unclear whether projects using it can also include
GPL-licensed code. Most distributions seem to be comfortable that
OpenSSL can be considered a "system library", so that linking to it
does not require OpenSSL to have a GPL-compatible license, but the
Free Software Foundation (FSF) and, unsurprisingly, Debian are not
on board with that interpretation. This licensing issue recently
reared its head again in a thread on the pgsql-hackers (PostgreSQL
development) mailing list.
"For command-line-oriented programs, the GNU readline library,
which allows various types for command-line editing, is a common
addition. But readline is licensed under the GPL (rather than the
LGPL), which means that programs which use it must have a
compatible license and PostgreSQL's BSD-ish permissive license
certainly qualifies. But the OpenSSL license puts additional
restrictions on its users and is thus not compatible with the GPL.
Whether that is a real problem in practice depends on how you
interpret the GPL and whether OpenSSL qualifies for the system
library exception."
