How to solve: /usr/lib/ruby/1.9.1/rubygems/custom_require.

Rakefile  Gemfile  README.md  LICENSE.txt  gmusic.gemspec  lib/  gmusic
tthtlchome:/home/tthtlc/gmusic>gem install gmusic
ERROR:  While executing gem ... (Gem::FilePermissionError)
    You don't have write permissions into the /var/lib/gems/1.9.1 directory.
tthtlchome:/home/tthtlc/gmusic>sudo gem install gmusic
Building native extensions.  This could take a while...
ERROR:  Error installing gmusic:
	ERROR: Failed to build gem native extension.

        /usr/bin/ruby1.9.1 extconf.rb
/usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require': cannot load such file -- mkmf (LoadError)
	from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
	from extconf.rb:1:in `<main>'


Gem files will remain installed in /var/lib/gems/1.9.1/gems/hpricot-0.8.6 for inspection.
Results logged to /var/lib/gems/1.9.1/gems/hpricot-0.8.6/ext/fast_xs/gem_make.out
tthtlchome:/home/tthtlc/gmusic>
tthtlchome:/home/tthtlc/gmusic>sudo aptitude install ruby1.9.1-dev
The following NEW packages will be installed:
  ruby1.9.1-dev
The following packages will be upgraded:
  libruby1.9.1 ruby1.9.1
2 packages upgraded, 1 newly installed, 0 to remove and 474 not upgraded.
Need to get 5,470 kB of archives. After unpacking 3,464 kB will be used.
Do you want to continue? [Y/n/?] Y
0% [Connecting to archive.ubuntu.com (2001:67c:1360:8c01::15)]
Get: 1 http://archive.ubuntu.com/ubuntu/ precise-updates/main ruby1.9.1 i386 1.9.3.0-1ubuntu2.7 [37.0 kB]
Get: 2 http://archive.ubuntu.com/ubuntu/ precise-updates/main libruby1.9.1 i386 1.9.3.0-1ubuntu2.7 [4,209 kB]
Get: 3 http://archive.ubuntu.com/ubuntu/ precise-updates/main ruby1.9.1-dev i386 1.9.3.0-1ubuntu2.7 [1,224 kB]
Fetched 5,470 kB in 6min 35s (13.8 kB/s)
(Reading database ... 256609 files and directories currently installed.)
Preparing to replace ruby1.9.1 1.9.3.0-1ubuntu2.4 (using .../ruby1.9.1_1.9.3.0-1ubuntu2.7_i386.deb) ...
Unpacking replacement ruby1.9.1 ...
Preparing to replace libruby1.9.1 1.9.3.0-1ubuntu2.4 (using .../libruby1.9.1_1.9.3.0-1ubuntu2.7_i386.deb) ...
Unpacking replacement libruby1.9.1 ...
Selecting previously unselected package ruby1.9.1-dev.
Unpacking ruby1.9.1-dev (from .../ruby1.9.1-dev_1.9.3.0-1ubuntu2.7_i386.deb) ...
Processing triggers for man-db ...
Setting up libruby1.9.1 (1.9.3.0-1ubuntu2.7) ...
Setting up ruby1.9.1 (1.9.3.0-1ubuntu2.7) ...
Setting up ruby1.9.1-dev (1.9.3.0-1ubuntu2.7) ...
Processing triggers for libc-bin ...
ldconfig deferred processing now taking place

Current status: 474 updates [-2].
tthtlchome:/home/tthtlc/gmusic>sudo gem install gmusic
[sudo] password for tthtlc:
Building native extensions.  This could take a while...
Fetching: gmusic-0.2.2.gem (100%)
Successfully installed hpricot-0.8.6
Successfully installed gmusic-0.2.2
2 gems installed
Installing ri documentation for hpricot-0.8.6...
Installing ri documentation for gmusic-0.2.2...
Installing RDoc documentation for hpricot-0.8.6...
Installing RDoc documentation for gmusic-0.2.2...
tthtlchome:/home/tthtlc/gmusic>d