1. Verify current version of PHP

Type in the following to see the current PHP version:

php -v

Should output something like:

PHP 5.3.3 (cli) (built: Jul 9 2015 17:39:00) 
Copyright (c) 1997-2010 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2010 Zend Technologies

Great, now we can move on!

2. Install the Remi and EPEL RPM repositories

If you haven’t already done so, install the Remi and EPEL repositories

wget https://dl.fedoraproject.org/pub/epel/epel-release-latest-6.noarch.rpm && rpm -Uvh epel-release-latest-6.noarch.rpm

wget http://rpms.famillecollet.com/enterprise/remi-release-6.rpm && rpm -Uvh remi-release-6*.rpm

Enable the REMI repository globally:

nano /etc/yum.repos.d/remi.repo

Under the section that looks like [remi] make the following changes:

[remi]
name=Remi's RPM repository for Enterprise Linux 6 - $basearch
#baseurl=http://rpms.remirepo.net/enterprise/6/remi/$basearch/
mirrorlist=http://rpms.remirepo.net/enterprise/6/remi/mirror
enabled=1
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-remi

Also, under the section that looks like [remi-php55] make the following changes:

[remi-php56]
name=Remi's PHP 5.6 RPM repository for Enterprise Linux 6 - $basearch
#baseurl=http://rpms.remirepo.net/enterprise/6/php56/$basearch/
mirrorlist=http://rpms.remirepo.net/enterprise/6/php56/mirror
# WARNING: If you enable this repository, you must also enable "remi"
enabled=1
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-remi

Type CTRL-O to save and CTRL-X to close the editor

3. Upgrade PHP 5.3 to PHP 5.6

Now we can upgrade PHP. Simply type in the following command:

yum -y upgrade php*

Once the update has completed, let’s verify that you have PHP 5.6 installed:

php -v

Should see output similar to the following:

PHP 5.6.14 (cli) (built: Sep 30 2015 14:07:43) 
Copyright (c) 1997-2015 The PHP Group
Zend Engine v2.6.0, Copyright (c) 1998-2015 Zend Technologies

如果要安装zabbix 3.0 还需安装php-mbstring、php-bcmath

安装php-mbstring：yum install -y php-mbstring php-bcmath

参考博文：https://www.zerostopbits.com/how-to-upgrade-php-5-3-to-php-5-6-on-centos-6-7/