当前系统，软件版本说明：
php 5.6.15 libxml 2.7.6 glibc 2.12 zlib 1.2.3 xz-libs 4.999.9
需求：
应开发的需求，线上环境，php-libxml版本升级到2.8以上。
升级步骤：
1、安装工具集
yum groupinstall -y 'development tools'
yum install kernel-headers -y
2、解决安装libxml2-1.9.0版本时，遇到的依赖关系
1）升级glibc版本 （ 版本 > glibc-2.12 ）
centos6系统，官方支持升级的最高版本是glibc-2.12（即yum升级支持的最高版本）。
wget http://ftp.redsleeve.org/pub/steam/glibc-2.15-60.el6.x86_64.rpm wget http://ftp.redsleeve.org/pub/steam/glibc-devel-2.15-60.el6.x86_64.rpm wget http://ftp.redsleeve.org/pub/steam/glibc-common-2.15-60.el6.x86_64.rpm wget http://ftp.redsleeve.org/pub/steam/glibc-headers-2.15-60.el6.x86_64.rpm rpm -Uvh glibc-2.15-60.el6.x86_64.rpm glibc-devel-2.15-60.el6.x86_64.rpm glibc-common-2.15-60.el6.x86_64.rpm glibc-headers-2.15-60.el6.x86_64.rpm
查看当前系统安装了glibc哪些包，以及最高支持版本：
# rpm -qa |grep glibc glibc-2.15-60.el6.x86_64 glibc-common-2.15-60.el6.x86_64 glibc-devel-2.15-60.el6.x86_64 glibc-headers-2.15-60.el6.x86_64 # strings /lib64/libc.so.6 | grep GLIBC GLIBC_2.2.5 GLIBC_2.2.6 GLIBC_2.3 GLIBC_2.3.2 GLIBC_2.3.3 GLIBC_2.3.4 GLIBC_2.4 GLIBC_2.5 GLIBC_2.6 GLIBC_2.7 GLIBC_2.8 GLIBC_2.9 GLIBC_2.10 GLIBC_2.11 GLIBC_2.12 GLIBC_2.13 GLIBC_2.14 GLIBC_2.15 GLIBC_PRIVATE
2）升级zlib版本 ( 版本 >= zlib-1.2.5 )
centos6系统，官方支持升级的最高版本是zlib-1.2.5。（即yum升级支持的最高版本）
wget http://ftp5.gwdg.de/pub/opensuse/repositories/home:/codice:/mono-redhat/CentOS_CentOS-6/x86_64/zlib-1.2.5-codice.4.1.x86_64.rpm wget http://ftp5.gwdg.de/pub/opensuse/repositories/home:/codice:/mono-redhat/CentOS_CentOS-6/x86_64/zlib-devel-1.2.5-codice.4.1.x86_64.rpm wget http://ftp5.gwdg.de/pub/opensuse/repositories/home:/codice:/mono-redhat/CentOS_CentOS-6/x86_64/zlib-static-1.2.5-codice.4.1.x86_64.rpm
rpm -Uvh zlib-1.2.5-codice.4.1.x86_64.rpm zlib-devel-1.2.5-codice.4.1.x86_64.rpm zlib-static-1.2.5-codice.4.1.x86_64.rpm
3）python2.7支持
centos6.5中，官方默认的Python版本为2.6。要装2.7版本，需要修改yum源。
yum install epel-release -y
wget https://centos6.iuscommunity.org/ius-release.rpm rpm -ivh ius-release.rpm yum clean all yum install python27 -y
4）升级xz-libs版本 ( 版本 > xz-libs-4.9 )
centos6.5，官方yum升级的最高版本是4.999.9
wget http://ftp.redsleeve.org/pub/steam/xz-libs-5.0.5-1.el6.x86_64.rpm wget http://ftp.redsleeve.org/pub/steam/xz-devel-5.0.5-1.el6.x86_64.rpm wget http://ftp.redsleeve.org/pub/steam/xz-5.0.5-1.el6.x86_64.rpm wget http://ftp.redsleeve.org/pub/steam/xz-lzma-compat-5.0.5-1.el6.x86_64.rpm wget http://ftp.redsleeve.org/pub/steam/xz-compat-libs-5.0.5-1.el6.x86_64.rpm rpm -Uvh xz-libs-5.0.5-1.el6.x86_64.rpm xz-devel-5.0.5-1.el6.x86_64.rpm xz-5.0.5-1.el6.x86_64.rpm xz-lzma-compat-5.0.5-1.el6.x86_64.rpm xz-compat-libs-5.0.5-1.el6.x86_64.rpm
3、升级libxml2
wget http://xmlsoft.org/sources/libxml2-devel-2.9.0-0rc0.x86_64.rpm wget http://xmlsoft.org/sources/libxml2-2.9.0-0rc0.x86_64.rpm wget http://xmlsoft.org/sources/libxml2-python-2.9.0-0rc0.x86_64.rpm
rpm -Uvh libxml2-2.9.0-0rc0.x86_64.rpm libxml2-devel-2.9.0-0rc0.x86_64.rpm libxml2-python-2.9.0-0rc0.x86_64.rpm
4、重新编译php
需要重新编译php，使升级的php-libxml生效。
进入php5.6.15的源码目录，重新编译php：
# cd php-5.6.15 # ./configure --prefix=/usr/local/php --with-config-file-path=/usr/local/php/etc --enable-fpm --enable-bcmath=shared --with-pdo_sqlite --with-gettext=shared --with-iconv --enable-ftp=shared --with-sqlite --with-sqlite3 --enable-mbstring=shared --enable-sockets=shared --enable-zip --enable-soap=shared --with-openssl --with-zlib --with-curl=shared --with-gd=shared --with-jpeg-dir --with-png-dir --with-freetype-dir --with-mcrypt=shared --with-mhash=shared --enable-opcache --with-mysql=mysqlnd --with-mysqli=shared,mysqlnd --with-pdo-mysql=shared,mysqlnd --without-pear --with-libdir=lib64 --disable-fileinfo # make
替换生成的php、php-cgi程序文件:
# /etc/init.d/php-fpm stop # mv /usr/local/php/bin/php /usr/local/php/bin/php.bak # mv /usr/local/php/bin/php-cgi /usr/local/php/bin/php-cgi.bak # cp -a sapi/cli/php /usr/local/php/bin/ # cp -a sapi/cgi/php-cgi /usr/local/php/bin/ # /etc/init.d/php-fpm start
查看php-libxml版本升级是否生效：
# /usr/local/php/bin/php -i|grep libxml libxml Version => 2.9.0 libxml libxml2 Version => 2.9.0
后续补充：
开启phpinfo访问，发现libxml版本仍是2.7.6。上述替换php、php-cgi程序的方法，是不能使得php-libxml版本升级生效的。
需要重新编译安装php（不同安装目录），才会生效。