I already have PHP and nginx installed and running on my on centOS 6.7. Please guide me, how can install glibc, glibc-common and GD libraries independently on my centOS 6.7 without crashing my system?
I am not sure how you installed PHP and nginx. If they are installed from CentOS6.7's Yum repository, you may install packages like glibc, glibc-common and GD by
# yum install glibc glibc-common php-gd