gem install pg can not bind to libpq - ruby

Question

After upgrading to Ruby 1.9.3 (from 1.9.2 using system RVM) on Ubuntu 10.04.3, I removed all of my gems, and attempted to reinstall pg (ala bundle install pg).
It then threw an error and informed me that I should look at mkmf.log, both of which are included in this gist: https://gist.github.com/d05a81701d968895c730
libpq-dev, libpq5, and postgresql-client are all installed and working correctly.
Pointing gem at pg_config, and the include and bin directories directly does not appear to change anything.
I've seen several questions about similar error messages around stackoverflow, and the rest of the web, but they all appear to be simple missing dependency issues (most of them are solved by installing libpq-dev), so I'm at a bit of a loss.
Various other properties that might be useful / relevant:
ruby 1.9.3p0 (2011-10-30 revision 33570) [i686-linux]
rvm 1.10.1 (system)
gem 1.8.15
psql (PostgreSQL) 8.4.9
Thanks in advance.
gem_make.out:
Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.
/usr/local/rvm/rubies/ruby-1.9.3-p0/bin/ruby extconf.rb
checking for pg_config... yes
Using config values from /usr/bin/pg_config
checking for libpq-fe.h... yes
checking for libpq/libpq-fs.h... yes
checking for PQconnectdb() in -lpq... no
checking for PQconnectdb() in -llibpq... no
checking for PQconnectdb() in -lms/libpq... no
Can't find the PostgreSQL client library (libpq)
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers. Check the mkmf.log file for more
details. You may need configuration options.
ldd.stdout:
$ldd /usr/lib/libpq.so
linux-gate.so.1 => (0xf57fe000)
libssl.so.0.9.8 => /lib/i686/cmov/libssl.so.0.9.8 (0xb77f4000)
libcrypto.so.0.9.8 => /lib/i686/cmov/libcrypto.so.0.9.8 (0xb76a2000)
libkrb5.so.3 => /usr/lib/libkrb5.so.3 (0xb75f1000)
libcom_err.so.2 => /lib/libcom_err.so.2 (0xb75ec000)
libgssapi_krb5.so.2 => /usr/lib/libgssapi_krb5.so.2 (0xb75bd000)
libcrypt.so.1 => /lib/tls/i686/cmov/libcrypt.so.1 (0xb758b000)
libldap_r-2.4.so.2 => /usr/lib/libldap_r-2.4.so.2 (0xb7544000)
libpthread.so.0 => /lib/tls/i686/cmov/libpthread.so.0 (0xb752b000)
libc.so.6 => /lib/tls/i686/cmov/libc.so.6 (0xb73d0000)
libdl.so.2 => /lib/tls/i686/cmov/libdl.so.2 (0xb73cc000)
libz.so.1 => /lib/libz.so.1 (0xb73b7000)
libk5crypto.so.3 => /usr/lib/libk5crypto.so.3 (0xb7393000)
libkrb5support.so.0 => /usr/lib/libkrb5support.so.0 (0xb738b000)
libkeyutils.so.1 => /lib/libkeyutils.so.1 (0xb7386000)
libresolv.so.2 => /lib/tls/i686/cmov/libresolv.so.2 (0xb7372000)
/lib/ld-linux.so.2 (0xb786a000)
liblber-2.4.so.2 => /usr/lib/liblber-2.4.so.2 (0xb7365000)
libsasl2.so.2 => /usr/lib/libsasl2.so.2 (0xb734d000)
libgnutls.so.26 => /usr/lib/libgnutls.so.26 (0xb72b2000)
libtasn1.so.3 => /usr/lib/libtasn1.so.3 (0xb72a0000)
libgcrypt.so.11 => /lib/libgcrypt.so.11 (0xb722d000)
libgpg-error.so.0 => /lib/libgpg-error.so.0 (0xb7228000)
pgconfig.stdout:
$pg_config --ldflags --libs
-Wl,-Bsymbolic-functions -Wl,--as-needed -Wl,--as-needed
-lpgport -lxslt -lxml2 -lpam -lssl -lcrypto -lkrb5 -lcom_err -lgssapi_krb5 -lz -lreadline -lcrypt -ldl -lm
mkmf.log:
find_executable: checking for pg_config... -------------------- yes
--------------------
find_header: checking for libpq-fe.h... -------------------- yes
"gcc -o conftest -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1/i686-linux -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1/ruby/backward -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1 -I. -I/usr/local/rvm/usr/include -D_FILE_OFFSET_BITS=64 -I/usr/include/postgresql -O3 -ggdb -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wimplicit-function-declaration -fPIC conftest.c -L. -L/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -Wl,-R/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -L/usr/local/rvm/usr/lib -Wl,-R/usr/local/rvm/usr/lib -L. -rdynamic -Wl,-export-dynamic -L/usr/lib -Wl,-R -Wl,/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -L/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -lruby -lpthread -lrt -ldl -lcrypt -lm -lc"
checked program was:
/* begin */
1: #include "ruby.h"
2:
3: int main() {return 0;}
/* end */
"gcc -E -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1/i686-linux -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1/ruby/backward -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1 -I. -I/usr/local/rvm/usr/include -D_FILE_OFFSET_BITS=64 -I/usr/include/postgresql -O3 -ggdb -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wimplicit-function-declaration -fPIC conftest.c -o conftest.i"
checked program was:
/* begin */
1: #include "ruby.h"
2:
3: #include <libpq-fe.h>
/* end */
--------------------
find_header: checking for libpq/libpq-fs.h... -------------------- yes
"gcc -E -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1/i686-linux -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1/ruby/backward -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1 -I. -I/usr/local/rvm/usr/include -D_FILE_OFFSET_BITS=64 -I/usr/include/postgresql -O3 -ggdb -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wimplicit-function-declaration -fPIC conftest.c -o conftest.i"
checked program was:
/* begin */
1: #include "ruby.h"
2:
3: #include <libpq/libpq-fs.h>
/* end */
--------------------
have_library: checking for PQconnectdb() in -lpq... -------------------- no
"gcc -o conftest -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1/i686-linux -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1/ruby/backward -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1 -I. -I/usr/local/rvm/usr/include -D_FILE_OFFSET_BITS=64 -I/usr/include/postgresql -O3 -ggdb -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wimplicit-function-declaration -fPIC conftest.c -L. -L/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -Wl,-R/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -L/usr/local/rvm/usr/lib -Wl,-R/usr/local/rvm/usr/lib -L. -rdynamic -Wl,-export-dynamic -L/usr/lib -Wl,-R -Wl,/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -L/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -lruby -lpq -lpthread -lrt -ldl -lcrypt -lm -lc"
/usr/lib/libpq.so: undefined reference to `X509_STORE_set_flags#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `CRYPTO_set_locking_callback#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `ENGINE_init#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `ENGINE_free#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `ENGINE_load_private_key#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `ENGINE_finish#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `X509_check_private_key#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `X509_free#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `SSL_CTX_new#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `SSL_pending#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `TLSv1_method#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `X509_STORE_load_locations#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `SSL_CTX_set_verify#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `ERR_pop_to_mark#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `SSL_new#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `SSL_get_error#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `ERR_get_error#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `ENGINE_by_id#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `SSL_write#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `SSL_load_error_strings#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `SSL_CTX_load_verify_locations#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `BIO_ctrl#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `PEM_read_bio_PrivateKey#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `CRYPTO_set_id_callback#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `SSL_free#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `BIO_free#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `SSL_CTX_get_cert_store#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `X509_get_subject_name#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `SSL_shutdown#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `SSL_CTX_set_client_cert_cb#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `PEM_read_bio_X509#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `ERR_set_mark#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `OPENSSL_config#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `X509_NAME_get_text_by_NID#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `SSL_read#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `SSL_CTX_ctrl#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `ERR_reason_error_string#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `SSL_get_peer_certificate#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `X509_NAME_oneline#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `SSL_set_ex_data#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `SSL_set_fd#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `SSL_library_init#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `CRYPTO_num_locks#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `SSL_get_ex_data#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `SSL_connect#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `BIO_new_file#OPENSSL_0.9.8'
collect2: ld returned 1 exit status
checked program was:
/* begin */
1: #include "ruby.h"
2:
3: #include <libpq-fe.h>
4:
5: /*top*/
6: int main() {return 0;}
7: int t() { void ((*volatile p)()); p = (void ((*)()))PQconnectdb; return 0; }
/* end */
"gcc -o conftest -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1/i686-linux -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1/ruby/backward -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1 -I. -I/usr/local/rvm/usr/include -D_FILE_OFFSET_BITS=64 -I/usr/include/postgresql -O3 -ggdb -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wimplicit-function-declaration -fPIC conftest.c -L. -L/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -Wl,-R/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -L/usr/local/rvm/usr/lib -Wl,-R/usr/local/rvm/usr/lib -L. -rdynamic -Wl,-export-dynamic -L/usr/lib -Wl,-R -Wl,/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -L/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -lruby -lpq -lpthread -lrt -ldl -lcrypt -lm -lc"
conftest.c: In function 't':
conftest.c:7: error: too few arguments to function 'PQconnectdb'
checked program was:
/* begin */
1: #include "ruby.h"
2:
3: #include <libpq-fe.h>
4:
5: /*top*/
6: int main() {return 0;}
7: int t() { PQconnectdb(); return 0; }
/* end */
--------------------
have_library: checking for PQconnectdb() in -llibpq... -------------------- no
"gcc -o conftest -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1/i686-linux -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1/ruby/backward -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1 -I. -I/usr/local/rvm/usr/include -D_FILE_OFFSET_BITS=64 -I/usr/include/postgresql -O3 -ggdb -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wimplicit-function-declaration -fPIC conftest.c -L. -L/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -Wl,-R/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -L/usr/local/rvm/usr/lib -Wl,-R/usr/local/rvm/usr/lib -L. -rdynamic -Wl,-export-dynamic -L/usr/lib -Wl,-R -Wl,/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -L/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -lruby -llibpq -lpthread -lrt -ldl -lcrypt -lm -lc"
/usr/bin/ld: cannot find -llibpq
collect2: ld returned 1 exit status
checked program was:
/* begin */
1: #include "ruby.h"
2:
3: #include <libpq-fe.h>
4:
5: /*top*/
6: int main() {return 0;}
7: int t() { void ((*volatile p)()); p = (void ((*)()))PQconnectdb; return 0; }
/* end */
"gcc -o conftest -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1/i686-linux -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1/ruby/backward -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1 -I. -I/usr/local/rvm/usr/include -D_FILE_OFFSET_BITS=64 -I/usr/include/postgresql -O3 -ggdb -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wimplicit-function-declaration -fPIC conftest.c -L. -L/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -Wl,-R/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -L/usr/local/rvm/usr/lib -Wl,-R/usr/local/rvm/usr/lib -L. -rdynamic -Wl,-export-dynamic -L/usr/lib -Wl,-R -Wl,/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -L/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -lruby -llibpq -lpthread -lrt -ldl -lcrypt -lm -lc"
conftest.c: In function 't':
conftest.c:7: error: too few arguments to function 'PQconnectdb'
checked program was:
/* begin */
1: #include "ruby.h"
2:
3: #include <libpq-fe.h>
4:
5: /*top*/
6: int main() {return 0;}
7: int t() { PQconnectdb(); return 0; }
/* end */
--------------------
have_library: checking for PQconnectdb() in -lms/libpq... -------------------- no
"gcc -o conftest -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1/i686-linux -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1/ruby/backward -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1 -I. -I/usr/local/rvm/usr/include -D_FILE_OFFSET_BITS=64 -I/usr/include/postgresql -O3 -ggdb -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wimplicit-function-declaration -fPIC conftest.c -L. -L/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -Wl,-R/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -L/usr/local/rvm/usr/lib -Wl,-R/usr/local/rvm/usr/lib -L. -rdynamic -Wl,-export-dynamic -L/usr/lib -Wl,-R -Wl,/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -L/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -lruby -lms/libpq -lpthread -lrt -ldl -lcrypt -lm -lc"
/usr/bin/ld: cannot find -lms/libpq
collect2: ld returned 1 exit status
checked program was:
/* begin */
1: #include "ruby.h"
2:
3: #include <libpq-fe.h>
4:
5: /*top*/
6: int main() {return 0;}
7: int t() { void ((*volatile p)()); p = (void ((*)()))PQconnectdb; return 0; }
/* end */
"gcc -o conftest -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1/i686-linux -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1/ruby/backward -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1 -I. -I/usr/local/rvm/usr/include -D_FILE_OFFSET_BITS=64 -I/usr/include/postgresql -O3 -ggdb -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wimplicit-function-declaration -fPIC conftest.c -L. -L/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -Wl,-R/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -L/usr/local/rvm/usr/lib -Wl,-R/usr/local/rvm/usr/lib -L. -rdynamic -Wl,-export-dynamic -L/usr/lib -Wl,-R -Wl,/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -L/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -lruby -lms/libpq -lpthread -lrt -ldl -lcrypt -lm -lc"
conftest.c: In function 't':
conftest.c:7: error: too few arguments to function 'PQconnectdb'
checked program was:
/* begin */
1: #include "ruby.h"
2:
3: #include <libpq-fe.h>
4:
5: /*top*/
6: int main() {return 0;}
7: int t() { PQconnectdb(); return 0; }
/* end */
--------------------

Answer 1

I've got the same problem in my case was lib's inside .rvm/usr/lib which was taken to this compilation instead of lib's from system. I'm not sure why that happens and why it doesn't work (in my case on Ubuntu 10.04 x86_64) but to solve it just :
mv ~/.rvm/usr/lib ~/.rvm/usr/lib_rvm
for a while or forever ;)
If someone will investigate why that happen I will be appreciate.
Regards.

Answer 2

Look at the mkmf.log around line 39:
"gcc -o conftest -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1/i686-linux -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1/ruby/backward -I/usr/local/rvm/rubies/ruby-1.9.3-p0/include/ruby-1.9.1 -I. -I/usr/local/rvm/usr/include -D_FILE_OFFSET_BITS=64 -I/usr/include/postgresql -O3 -ggdb -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wimplicit-function-declaration -fPIC conftest.c -L. -L/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -Wl,-R/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -L/usr/local/rvm/usr/lib -Wl,-R/usr/local/rvm/usr/lib -L. -rdynamic -Wl,-export-dynamic -L/usr/lib -Wl,-R -Wl,/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -L/usr/local/rvm/rubies/ruby-1.9.3-p0/lib -lruby -lpq -lpthread -lrt -ldl -lcrypt -lm -lc"
/usr/lib/libpq.so: undefined reference to `X509_STORE_set_flags#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `CRYPTO_set_locking_callback#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `ENGINE_init#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `ENGINE_free#OPENSSL_0.9.8'
/usr/lib/libpq.so: undefined reference to `ENGINE_load_private_key#OPENSSL_0.9.8'
...
Smells like a missing OpenSSL. I also don't see a -lssl in the library list but the missing symbols suggest that it should be there.
So try installing the OpenSSL libraries (version 0.9.8 by the look of things). Then see if pg_config --libs contains -lssl or similar and try again. If all of this works then you might want to send a bug report to the Ubuntu people so that they can fix the libpq-dev dependencies.
Sorry, I don't have an Ubuntu set up anywhere accessible at the moment so there is some guesswork going on here.

Answer 3

Don't be fooled by the SSL lib being installed - have a look at your Ruby build and check the ssl build log there. I've been bitten by that one before. Other libraries that sometimes don't get loaded are the GZip ones. This may not be the problem but have a look.
UPDATE:
You need the -dev libraries.
These days I use rbenv or one of the other ruby build tools and follow whatever messages they spit out.