Installing Ruby on Rails should be a straight forward exercise. At high level, it should be just a matter of installing Ruby and then followed by installing Rails

>apt-get install ruby-full
>gem install rails

In my case, I have hit a few issues and below is the my notes which may be useful to anyone who may experience the same problems.

Install Ruby

Firstly, installing Ruby using Debian package manager (apt-get)

>apt-get install ruby-full

The process completed without any error / issue.

Install Rails – nokogiri – You have to install development tools first

After Ruby is install, use Ruby package manager (gem) to install Rails

>gem install rails

Failed with the following error output

...
Fetching: mini_portile2-2.0.0.gem (100%)
Successfully installed mini_portile2-2.0.0
Fetching: nokogiri-1.6.7.gem (100%)
Building native extensions.  This could take a while...
ERROR:  Error installing rails:
ERROR: Failed to build gem native extension.

/usr/bin/ruby2.1 extconf.rb
checking if the C compiler accepts ... *** 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.

/usr/lib/ruby/2.1.0/mkmf.rb:456:in `try_do': The compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.
from /usr/lib/ruby/2.1.0/mkmf.rb:571:in `block in try_compile'
from /usr/lib/ruby/2.1.0/mkmf.rb:522:in `with_werror'
from /usr/lib/ruby/2.1.0/mkmf.rb:571:in `try_compile'
from extconf.rb:80:in `nokogiri_try_compile'
from extconf.rb:87:in `block in add_cflags'
from /usr/lib/ruby/2.1.0/mkmf.rb:621:in `with_cflags'
from extconf.rb:86:in `add_cflags'
from extconf.rb:336:in `<main>'

extconf failed, exit code 1

Gem files will remain installed in /var/lib/gems/2.1.0/gems/nokogiri-1.6.7 for inspection.
Results logged to /var/lib/gems/2.1.0/extensions/x86-linux/2.1.0/nokogiri-1.6.7/gem_make.out

Checked /var/lib/gems/2.1.0/extensions/x86-linux/2.1.0/nokogiri-1.6.7/gem_make.out and it contains the same information above.

The part of the error messages

checking if the C compiler accepts ... *** 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.

suggests error occurred when trying to compile some C code.

This part of the error messages

/usr/lib/ruby/2.1.0/mkmf.rb:456:in `try_do': The compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.

seems to suggests perhaps “development tools” are missing?

Checked /var/lib/gems/2.1.0/extensions/x86-linux/2.1.0/nokogiri-1.6.7/mkmf.log and found

"gcc -o conftest -I/usr/include/i386-linux-gnu/ruby-2.1.0 -I/usr/include/ruby-2.1.0/ruby/backward -I/usr/include/ruby-2.1.0 -I. -D_FORTIFY_SOURCE=2 -D_FILE_OFFSET_BITS=64  -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -fPIC  conftest.c  -L. -L/usr/lib/i386-linux-gnu -L. -Wl,-z,relro -L/build/ruby2.1-uTcziZ/ruby2.1-2.1.5/debian/lib -fstack-protector -rdynamic -Wl,-export-dynamic     -lruby-2.1  -lpthread -lgmp -ldl -lcrypt -lm   -lc "

checked program was:
/* begin */
1: #include "ruby.h"
2:
3: int main(int argc, char **argv)
4: {
5:   return 0;
6: }
/* end */

This suggests that error found when running gcc to compile something. Because of “You have to install development tools first”.

I tried to run gcc (GNU C compiler) directly

>which gcc
>gcc
-su: gcc: command not found

Up to this point, I have not tried to compile any C code on this Debian machine and was not too surprise to see gcc is missing. Check the package database

>dpkg --list | grep compiler
ii  gcc-4.8                        4.8.4-1                   i386         GNU C compiler
ii  libllvm3.5:i386                1:3.5-10                  i386         Modular compiler and toolchain technologies, runtime library
ii  linux-compiler-gcc-4.8-x86     3.16.7-ckt11-1+deb8u6     i386         Compiler for Linux on x86 (meta-package)

It is installed based on the package database but anyway, proceed to install gcc to get the latest version.

>apt-get install gcc

Check gcc after installation

>which gcc
/usr/bin/gcc

The above compile error is resolved but new error appeared.

Install Rails – nokogiri – zlib is missing; necessary for building libxml2

Second attempt to use Ruby package manager (gem) to install Rails and got the following errors

>gem install rails

...
Building native extensions.  This could take a while...
ERROR:  Error installing rails:
ERROR: Failed to build gem native extension.

/usr/bin/ruby2.1 extconf.rb
checking if the C compiler accepts ... yes
Building nokogiri using packaged libraries.
Using mini_portile version 2.0.0
checking for gzdopen() in -lz... no
zlib is missing; necessary for building libxml2
*** 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.
...
extconf failed, exit code 1

Gem files will remain installed in /var/lib/gems/2.1.0/gems/nokogiri-1.6.7 for inspection.
Results logged to /var/lib/gems/2.1.0/extensions/x86-linux/2.1.0/nokogiri-1.6.7/gem_make.out

Note the following line in the output

checking if the C compiler accepts ... yes

indicates that the previous error have been resolved – C compiler is present and working.

Checked /var/lib/gems/2.1.0/extensions/x86-linux/2.1.0/nokogiri-1.6.7/gem_make.out and it contains the same information above.

The following part of the error messages

Using mini_portile version 2.0.0
checking for gzdopen() in -lz... no
zlib is missing; necessary for building libxml2
 *** 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.
...
extconf failed, exit code 1

suggests that something is missing when trying to build libxml2.

Checked /var/lib/gems/2.1.0/extensions/x86-linux/2.1.0/nokogiri-1.6.7/mkmf.log and found

...
"gcc -o conftest -I/usr/include/i386-linux-gnu/ruby-2.1.0 -I/usr/include/ruby-2.1.0/ruby/backward -I/usr/include/ruby-2.1.0 -I. -D_FORTIFY_SOURCE=2 -D_FILE_OFFSET_BITS=64  -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -fPIC  -g -DXP_UNIX -Wall -Wcast-qual -Wwrite-strings -Wconversion -Wmissing-noreturn -Winline conftest.c  -L. -L/usr/lib/i386-linux-gnu -L. -Wl,-z,relro -L/build/ruby2.1-uTcziZ/ruby2.1-2.1.5/debian/lib -fstack-protector -rdynamic -Wl,-export-dynamic     -lruby-2.1 -lz  -lpthread -lgmp -ldl -lcrypt -lm   -lc "
conftest.c:3:18: fatal error: zlib.h: No such file or directory
#include <zlib.h>
^
compilation terminated.
checked program was:
/* begin */
1: #include "ruby.h"
2:
3: #include <zlib.h>
4:
5: /*top*/
6: extern int t(void);
7: int main(int argc, char **argv)
8: {
9:   if (argc > 1000000) {
10:     printf("%p", &t);
11:   }
12:
13:   return 0;
14: }
15: int t(void) { void ((*volatile p)()); p = (void ((*)()))gzdopen; return 0; }
/* end */

From this part of the messags

conftest.c:3:18: fatal error: zlib.h: No such file or directory

it is clear that zlib.h header file is missing. The missing header file issue is resolved by installing zlib1g-dev package

apt-get install zlib1g-dev

Install Rails – nokogiri – mini_portile.rb:344:in `spawn’: No such file or directory – make (Errno::ENOENT)

Third attempt to use Ruby package manager (gem) to install Rails and got the following errors

>gem install rails
Building native extensions.  This could take a while...
ERROR:  Error installing rails:
ERROR: Failed to build gem native extension.

/usr/bin/ruby2.1 extconf.rb
checking if the C compiler accepts ... yes
Building nokogiri using packaged libraries.
Using mini_portile version 2.0.0
checking for gzdopen() in -lz... yes
...
Running 'configure' for libxml2 2.9.2... OK
Running 'compile' for libxml2 2.9.2... *** 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.
...
--disable-cross-build
/var/lib/gems/2.1.0/gems/mini_portile2-2.0.0/lib/mini_portile2/mini_portile.rb:344:in `spawn': No such file or directory - make (Errno::ENOENT)
from /var/lib/gems/2.1.0/gems/mini_portile2-2.0.0/lib/mini_portile2/mini_portile.rb:344:in `block in execute'
from /var/lib/gems/2.1.0/gems/mini_portile2-2.0.0/lib/mini_portile2/mini_portile.rb:337:in `chdir'
from /var/lib/gems/2.1.0/gems/mini_portile2-2.0.0/lib/mini_portile2/mini_portile.rb:337:in `execute'
from /var/lib/gems/2.1.0/gems/mini_portile2-2.0.0/lib/mini_portile2/mini_portile.rb:111:in `compile'
from /var/lib/gems/2.1.0/gems/mini_portile2-2.0.0/lib/mini_portile2/mini_portile.rb:150:in `cook'
from extconf.rb:289:in `block (2 levels) in process_recipe'
from extconf.rb:182:in `block in chdir_for_build'
from extconf.rb:181:in `chdir'
from extconf.rb:181:in `chdir_for_build'
from extconf.rb:288:in `block in process_recipe'
from extconf.rb:187:in `tap'
from extconf.rb:187:in `process_recipe'
from extconf.rb:478:in `<main>'

extconf failed, exit code 1

Gem files will remain installed in /var/lib/gems/2.1.0/gems/nokogiri-1.6.7 for inspection.
Results logged to /var/lib/gems/2.1.0/extensions/x86-linux/2.1.0/nokogiri-1.6.7/gem_make.out

Checked the make file output file and no additional information available in mkmf.out

This part of the error messages

/var/lib/gems/2.1.0/gems/mini_portile2-2.0.0/lib/mini_portile2/mini_portile.rb:344:in `spawn': No such file or directory - make (Errno::ENOENT)

suggests that errors at line 344 in /var/lib/gems/2.1.0/gems/mini_portile2-2.0.0/lib/mini_portile2/mini_portile.rb

Here is the list of line 337 to 345 in /var/lib/gems/2.1.0/gems/mini_portile2-2.0.0/lib/mini_portile2/mini_portile.rb

Dir.chdir (options.fetch(:cd){ work_path }) do
if options.fetch(:initial_message){ true }
message "Running '#{action}' for #{@name} #{@version}... "
end

if Process.respond_to?(:spawn) && ! RbConfig.respond_to?(:java)
args = [command].flatten + [{[:out, :err]=>[log_out, "a"]}]
pid = spawn(*args)
Process.wait(pid)

The “stacktrace” in the error messages match up the method call and line number of the above listing.

Note that ::spawn() is a ruby method – according to Ruby documentation, it spawn a new process and then call exec() and pass a command as parameter.  Errno::ENOENT means specified command in the paramter cannot be found.

I followed the upstream logic flow based on the stack trace  – some command parameter is missing so it seems to be some sort of internal error – highly unlikely the result of missing libraries or header files.

Checked nokogiri site if there known issue which may cause the problem, found the installation and troubleshooting guide for Debian / Ubuntu and followed the provided instructions

> apt-get install build-essential patch
> apt-get install ruby-dev zlib1g-dev

Next, instead of trying to install Rails again, I tried installing nokogiri instead

> gem install nokogiri

and it installed OK and then tried installing Rails again.

> gem install rails

Success !