rajibkhansumon
To install and run osTicket the following components are required;

Web Server: Apache or IIS
PHP Version: 5.6+
MySQL Database: 5.0+

You have not supplied the webserver (and version) that you are using.
Your PHP version is indeed too low and you should upgrade.
Also since you are running CentOS are you also running SELinux?

Web Server Apache
php version : 5.4
SELinux is disabled

after php version upgrade php 5.4 to 5.6 showing bellow error. how can i do this in this situation

IMAP doesn't exist. PHP must be compiled with IMAP enabled.

    ntozier php upgrade done to 5.6 but still getting bellow error

    POP3 connection broken in response

    php upgrade done to 5.6 but still getting bellow error

    POP3 connection broken in response

    ntozier php upgrade and imap installation done but still getting bellow error

    POP3 connection broken in response

      You install PHP-imap usually by doing something like:

      apt-get install php-imap

      Doing so should install imap and make it available to PHP. It sounds like you have installed IMAP not the PHP IMAP package needed.

        Sorry I do not follow. You are all set, but want to know what to do in the current situation?
        Those two statements seem to contradict each other.

        Please provide the full error.
        Anything in PHP error logs?
        Is this self hosted or do you have a hosting account with a hosting company?