#2 楼 @newlife_in_s1 我现在有这个问题，请问具体是怎么解决的！

#5 楼 @chenjau 恩恩！

#4 楼 @jiemoon 改了之后还是出现 ActiveRecord::PendingMigrationError 这个错误。

#2 楼 @amateur 报错如下

davidlee:smaple_app ft_david$ RAILS_ENV=development rake db:migrate
== 20160705132939 AddIndexToUsersEmail: migrating =============================
-- add_index(:users, :email, {:unqiue=>true})
rake aborted!
StandardError: An error has occurred, this and all later migrations canceled:

Unknown key: :unqiue. Valid keys are: :unique, :order, :name, :where, :length, :internal, :using, :algorithm, :type
/Users/ft_david/.rvm/gems/ruby-2.3.0/gems/activesupport-4.2.6/lib/active_support/core_ext/hash/keys.rb:75:in `block in assert_valid_keys'

#13 楼 @liwei78 我现在也是这个问题，请问具体怎么操作才能解决这个问题！

#6 楼 @catherine 才搞了两天！

#4 楼 @catherine 谢谢了，我在 Github 上找到了答案https://github.com/sparklemotion/nokogiri/issues/1483

#10 楼 @twairball 具体运行什么命令？

#1 楼 @qinfanpeng 我按照你说的运行了gem install nokogiri -v '1.6.8' 报错是这样的

davidlee:toyApp ft_david$ gem install nokogiri -v '1.6.8'
Building native extensions.  This could take a while...
ERROR:  Error installing nokogiri:
    ERROR: Failed to build gem native extension.

    current directory: /Users/ft_david/.rvm/gems/ruby-2.3.0/gems/nokogiri-1.6.8/ext/nokogiri
/Users/ft_david/.rvm/rubies/ruby-2.3.0/bin/ruby -r ./siteconf20160629-5178-ltghsy.rb extconf.rb
Using pkg-config version 1.1.7
checking if the C compiler accepts ... yes
checking if the C compiler accepts -Wno-error=unused-command-line-argument-hard-error-in-future... no
Building nokogiri using packaged libraries.
Using mini_portile version 2.1.0
checking for iconv.h... yes
checking for gzdopen() in -lz... yes
checking for iconv using --with-opt-* flags... yes
************************************************************************
IMPORTANT NOTICE:

Building Nokogiri with a packaged version of libxml2-2.9.4.

Team Nokogiri will keep on doing their best to provide security
updates in a timely manner, but if this is a concern for you and want
to use the system library instead; abort this installation process and
reinstall nokogiri as follows:

    gem install nokogiri -- --use-system-libraries
        [--with-xml2-config=/path/to/xml2-config]
        [--with-xslt-config=/path/to/xslt-config]

If you are using Bundler, tell it to use the option:

    bundle config build.nokogiri --use-system-libraries
    bundle install

Note, however, that nokogiri is not fully compatible with arbitrary
versions of libxml2 provided by OS/package vendors.
************************************************************************
Extracting libxml2-2.9.4.tar.gz into tmp/x86_64-apple-darwin15.4.0/ports/libxml2/2.9.4... OK
Running 'configure' for libxml2 2.9.4... OK
Running 'compile' for libxml2 2.9.4... ERROR, review '/Users/ft_david/.rvm/gems/ruby-2.3.0/gems/nokogiri-1.6.8/ext/nokogiri/tmp/x86_64-apple-darwin15.4.0/ports/libxml2/2.9.4/compile.log' to see what happened. Last lines are:
========================================================================
    unsigned short* in = (unsigned short*) inb;
                         ^~~~~~~~~~~~~~~~~~~~~
encoding.c:815:27: warning: cast from 'unsigned char *' to 'unsigned short *' increases required alignment from 1 to 2 [-Wcast-align]
    unsigned short* out = (unsigned short*) outb;
                          ^~~~~~~~~~~~~~~~~~~~~~
4 warnings generated.
  CC       error.lo
  CC       parserInternals.lo
  CC       parser.lo
  CC       tree.lo
  CC       hash.lo
  CC       list.lo
  CC       xmlIO.lo
xmlIO.c:1450:52: error: use of undeclared identifier 'LZMA_OK'
    ret =  (__libxml2_xzclose((xzFile) context) == LZMA_OK ) ? 0 : -1;
                                                   ^
1 error generated.
make[2]: *** [xmlIO.lo] Error 1
make[1]: *** [all-recursive] Error 1
make: *** [all] Error 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.

Provided configuration options:
    --with-opt-dir
    --with-opt-include
    --without-opt-include=${opt-dir}/include
    --with-opt-lib
    --without-opt-lib=${opt-dir}/lib
    --with-make-prog
    --without-make-prog
    --srcdir=.
    --curdir
    --ruby=/Users/ft_david/.rvm/rubies/ruby-2.3.0/bin/$(RUBY_BASE_NAME)
    --help
    --clean
    --use-system-libraries
    --enable-static
    --disable-static
    --with-zlib-dir
    --without-zlib-dir
    --with-zlib-include
    --without-zlib-include=${zlib-dir}/include
    --with-zlib-lib
    --without-zlib-lib=${zlib-dir}/lib
    --enable-cross-build
    --disable-cross-build
/Users/ft_david/.rvm/gems/ruby-2.3.0/gems/mini_portile2-2.1.0/lib/mini_portile2/mini_portile.rb:366:in `block in execute': Failed to complete compile task (RuntimeError)
    from /Users/ft_david/.rvm/gems/ruby-2.3.0/gems/mini_portile2-2.1.0/lib/mini_portile2/mini_portile.rb:337:in `chdir'
    from /Users/ft_david/.rvm/gems/ruby-2.3.0/gems/mini_portile2-2.1.0/lib/mini_portile2/mini_portile.rb:337:in `execute'
    from /Users/ft_david/.rvm/gems/ruby-2.3.0/gems/mini_portile2-2.1.0/lib/mini_portile2/mini_portile.rb:111:in `compile'
    from /Users/ft_david/.rvm/gems/ruby-2.3.0/gems/mini_portile2-2.1.0/lib/mini_portile2/mini_portile.rb:150:in `cook'
    from extconf.rb:364:in `block (2 levels) in process_recipe'
    from extconf.rb:257:in `block in chdir_for_build'
    from extconf.rb:256:in `chdir'
    from extconf.rb:256:in `chdir_for_build'
    from extconf.rb:363:in `block in process_recipe'
    from extconf.rb:262:in `tap'
    from extconf.rb:262:in `process_recipe'
    from extconf.rb:555:in `<main>'

To see why this extension failed to compile, please check the mkmf.log which can be found here:

  /Users/ft_david/.rvm/gems/ruby-2.3.0/extensions/x86_64-darwin-15/2.3.0/nokogiri-1.6.8/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in /Users/ft_david/.rvm/gems/ruby-2.3.0/gems/nokogiri-1.6.8 for inspection.
Results logged to /Users/ft_david/.rvm/gems/ruby-2.3.0/extensions/x86_64-darwin-15/2.3.0/nokogiri-1.6.8/gem_make.out

#8 楼 @verfino apt-get install 这个是什么命令？

我在安装 rails 的时候出现同样的问题现在还没解决。