gem to install the libyajl2 c-library for distributions which do not have it
To build this depends on libgmp and its headers being installed. On Ubuntu:
apt-get install libgmp-dev
If you get a mysterious "unhandled exception" build failure like:
Building native extensions. This could take a while...
ERROR: Error installing libyajl2:
ERROR: Failed to build gem native extension.
/home/lamont/.rvm/rubies/ruby-2.2.3/bin/ruby -r ./siteconf20151209-53133-1aq7vdk.rb extconf.rb
creating Makefile
/home/lamont/.rvm/gems/ruby-2.2.3/gems/libyajl2-1.2.0/ext/libyajl2
extconf.rb:104:in `makemakefiles': unhandled exception
from extconf.rb:138:in `<main>'
extconf failed, exit code 1
Gem files will remain installed in /home/lamont/.rvm/gems/ruby-2.2.3/gems/libyajl2-1.2.0 for inspection.
Results logged to /home/lamont/.rvm/gems/ruby-2.2.3/extensions/x86_64-linux/2.2.0/libyajl2-1.2.0/gem_make.out
Look at the output of make.out in the same directory as extconf.rb, for my example above that looks like:
# cat /home/lamont/.rvm/gems/ruby-2.2.3/gems/libyajl2-1.2.0/ext/libyajl2/make.out
compiling yajl_buf.c
compiling yajl.c
compiling yajl_gen.c
compiling yajl_tree.c
compiling yajl_encode.c
compiling yajl_parser.c
compiling yajl_alloc.c
compiling yajl_version.c
compiling yajl_lex.c
linking shared-object libyajl.so
/usr/bin/ld: cannot find -lgmp
collect2: error: ld returned 1 exit status
make: *** [libyajl.so] Error 1
Which gives the correct error that -lgmp was not found...