I got this "popular" error while installing mysql2 gem on Debian Squeeze:
gem install mysql2 Building native extensions. This could take a while... ERROR: Error installing mysql2: ERROR: Failed to build gem native extension. /usr/local/rvm/rubies/ruby-1.9.2-p290/bin/ruby extconf.rb checking for rb_thread_blocking_region()... yes checking for rb_wait_for_single_fd()... no checking for mysql.h... yes checking for errmsg.h... yes checking for mysqld_error.h... yes creating Makefile make gcc -I. -I/usr/local/rvm/rubies/ruby-1.9.2-p290/include/ruby-1.9.1/i686-linux -I/usr/local/rvm/rubies/ruby-1.9.2-p290/include/ruby-1.9.1/ruby/backward -I/usr/local/rvm/rubies/ruby-1.9.2-p290/include/ruby-1.9.1 -I. -DHAVE_RB_THREAD_BLOCKING_REGION -DHAVE_MYSQL_H -DHAVE_ERRMSG_H -DHAVE_MYSQLD_ERROR_H -D_FILE_OFFSET_BITS=64 -I/usr/include/mysql -DBIG_JOINS=1 -fno-strict-aliasing -g -fPIC -O3 -ggdb -Wextra -Wno-unused-parameter -Wno-parentheses -Wpointer-arith -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -fPIC -Wall -funroll-loops -o client.o -c client.c gcc -I. -I/usr/local/rvm/rubies/ruby-1.9.2-p290/include/ruby-1.9.1/i686-linux -I/usr/local/rvm/rubies/ruby-1.9.2-p290/include/ruby-1.9.1/ruby/backward -I/usr/local/rvm/rubies/ruby-1.9.2-p290/include/ruby-1.9.1 -I. -DHAVE_RB_THREAD_BLOCKING_REGION -DHAVE_MYSQL_H -DHAVE_ERRMSG_H -DHAVE_MYSQLD_ERROR_H -D_FILE_OFFSET_BITS=64 -I/usr/include/mysql -DBIG_JOINS=1 -fno-strict-aliasing -g -fPIC -O3 -ggdb -Wextra -Wno-unused-parameter -Wno-parentheses -Wpointer-arith -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -fPIC -Wall -funroll-loops -o mysql2_ext.o -c mysql2_ext.c gcc -I. -I/usr/local/rvm/rubies/ruby-1.9.2-p290/include/ruby-1.9.1/i686-linux -I/usr/local/rvm/rubies/ruby-1.9.2-p290/include/ruby-1.9.1/ruby/backward -I/usr/local/rvm/rubies/ruby-1.9.2-p290/include/ruby-1.9.1 -I. -DHAVE_RB_THREAD_BLOCKING_REGION -DHAVE_MYSQL_H -DHAVE_ERRMSG_H -DHAVE_MYSQLD_ERROR_H -D_FILE_OFFSET_BITS=64 -I/usr/include/mysql -DBIG_JOINS=1 -fno-strict-aliasing -g -fPIC -O3 -ggdb -Wextra -Wno-unused-parameter -Wno-parentheses -Wpointer-arith -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -fPIC -Wall -funroll-loops -o result.o -c result.c result.c: In function ‘rb_mysql_result_fetch_fields’: result.c:381: warning: comparison between signed and unsigned integer expressions gcc -shared -o mysql2.so client.o mysql2_ext.o result.o -L. -L/usr/local/rvm/rubies/ruby-1.9.2-p290/lib -Wl,-R/usr/local/rvm/rubies/ruby-1.9.2-p290/lib -L. -rdynamic -Wl,-export-dynamic -Wl,-rpath,/usr/lib -Wl,-R -Wl,/usr/local/rvm/rubies/ruby-1.9.2-p290/lib -L/usr/local/rvm/rubies/ruby-1.9.2-p290/lib -lruby -L/usr/lib -lmysqlclient_r -lpthread -lz -lm -lrt -lssl -lcrypto -ldl -lpthread -lrt -ldl -lcrypt -lm -lc /usr/bin/ld: cannot find -lmysqlclient_r collect2: ld returned 1 exit status make: *** [mysql2.so] Error 1 Gem files will remain installed in /usr/local/rvm/gems/ruby-1.9.2-p290/gems/mysql2-0.3.11 for inspection. Results logged to /usr/local/rvm/gems/ruby-1.9.2-p290/gems/mysql2-0.3.11/ext/mysql2/gem_make.out There are a lot of search results at stack overflow but none of them would fix my Problem.
libmysqlclient-dev - MySQL database development files libmysqlclient18 - MySQL database client library are installed via dot deb repo.
mysql-server is installed, too.
The following files related to libmysqlclient could be found at /usr/lib
/usr/lib/libmysqlclient.so.18 /usr/lib/libmysqlclient_r /usr/lib/libmysqlclient.so /usr/lib/libmysqlclient.so.16.0.0 /usr/lib/libmysqlclient.a /usr/lib/libmysqlclient_r.so.16 /usr/lib/libmysqlclient.so.16 /usr/lib/libmysqlclient.so.18.0.0 /usr/lib/libmysqlclient_r.so.16.0.0