iRedMail requires a new/fresh/clean server for installation. So, my questions are:

*) is your server a fresh/clean one before iRedMail installation?
*) Do you have MySQL server running and have mysql root password set before iRedMail installation?

I have no idea if you cannot provide futher debug message. The easiest way to solve it is trying to install iRedMail on a fresh/clean server again.

Could you please check whether mysql is installed manually before iRedMail installation? For example:

# rpm -qa | grep -i mysql

We tested CentOS many times, no issue at all.

It's hard to say what the problem is without debug. Could you please modify file 'functions/backend.sh' like below and try again?

*) Find below line in functions/backend.sh:

    elif [ X"${BACKEND}" == X"MYSQL" ]; then                                       
        ECHO_INFO "Configure MySQL database server."                               
        mysql_generate_defauts_file_root                                           
        if [ X"${USE_LOCAL_MYSQL_SERVER}" == X'YES' ]; then                        
            check_status_before_run mysql_initialize                               
        fi                                                                         
        check_status_before_run mysql_import_vmail_users

*) Add two lines there: One is 'set -x', another one is 'set +x':

    elif [ X"${BACKEND}" == X"MYSQL" ]; then                                       
        ECHO_INFO "Configure MySQL database server."
        set -x
        mysql_generate_defauts_file_root
        if [ X"${USE_LOCAL_MYSQL_SERVER}" == X'YES' ]; then
            check_status_before_run mysql_initialize
        fi
        check_status_before_run mysql_import_vmail_users
        set +x

*) Save above change, then install this modified iRedMail on this server (must be a new/fresh/clean server).

With modified functions/backend.sh, it will print debug message about how the shell scripts work, so that we can dig deeper to try to understand why your issue happened.

< INFO > Create self-signed SSL certification files.
< INFO > Create required system accounts: vmail, iredapd, iredadmin.
< INFO > Configure Apache web server and PHP.
< INFO > Configure MySQL database server.
+ mysql_generate_defauts_file_root
+ ECHO_DEBUG 'Generate temporary defauts file for MySQL client option --defaults-file: /root/iRedMail-0.8.6/.mysql-root-defaults-file.'
+ '[' XNO == XYES ']'
+ :
+ cat
+ '[' XYES == XYES ']'
+ check_status_before_run mysql_initialize
+ _status=status_mysql_initialize
++ eval echo '$status_mysql_initialize'
+++ echo
+ '[' X '!=' XDONE ']'
+ mysql_initialize
+ ECHO_DEBUG 'Starting MySQL.'
+ '[' XNO == XYES ']'
+ :
+ '[' XUBUNTU == XOPENBSD ']'
+ freebsd_enable_service_in_rc_conf mysql_enable YES
+ '[' XUBUNTU == XFREEBSD ']'
+ ECHO_DEBUG 'Copy sample/my.cnf to /etc/mysql/my.cnf.'
+ '[' XNO == XYES ']'
+ :
+ '[' '!' -f /etc/mysql/my.cnf ']'
+ perl -pi -e 's#^(skip-networking.*)#${1}#' /etc/mysql/my.cnf
+ grep '^innodb_file_per_table' /etc/mysql/my.cnf
+ '[' X1 '!=' X0 ']'
+ perl -pi -e 's#^(\[mysqld\])#${1}\ninnodb_file_per_table#' /etc/mysql/my.cnf
+ /etc/init.d/mysql restart
+ ECHO_DEBUG 'Sleep 5 seconds for MySQL daemon initialize ...'
+ '[' XNO == XYES ']'
+ :
+ sleep 5
+ '[' X127.0.0.1 == X127.0.0.1 ']'
+ mysql -uroot -e 'show databases'
+ '[' X0 == X0 ']'
+ ECHO_DEBUG 'Setting password for MySQL admin (root).'
+ '[' XNO == XYES ']'
+ :
+ mysqladmin --user=root password XXXXXXXXXXXXXX
+ echo ''
+ cat
+ ECHO_DEBUG 'Initialize MySQL database.'
+ '[' XNO == XYES ']'
+ :
+ mysql --defaults-file=/root/iRedMail-0.8.6/.mysql-root-defaults-file
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)
+ cat
+ echo 'export status_mysql_initialize="DONE"'
+ check_status_before_run mysql_import_vmail_users
+ _status=status_mysql_import_vmail_users
++ eval echo '$status_mysql_import_vmail_users'
+++ echo
+ '[' X '!=' XDONE ']'
+ mysql_import_vmail_users
+ ECHO_DEBUG 'Generating SQL template for postfix virtual hosts: /root/iRedMail-0.8.6/conf/mysql_vmail.sql.'
+ '[' XNO == XYES ']'
+ :
++ gen_md5_passwd XXXXXXXXX
++ openssl passwd -1 XXXXXXXXX
+ export 'DOMAIN_ADMIN_PASSWD=XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
+ DOMAIN_ADMIN_PASSWD='XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
++ gen_md5_passwd XXXXXXXX
++ openssl passwd -1 XXXXXXXX
+ export 'FIRST_USER_PASSWD=XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
+ FIRST_USER_PASSWD='XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
+ perl -pi -e 's#(.*storagebasedirectory.*DEFAULT).*#${1} "$ENV{STORAGE_BASE_DIR}",#' /root/iRedMail-0.8.6/samples/iredmail.mysql
+ perl -pi -e 's#(.*storagenode.*DEFAULT).*#${1} "$ENV{STORAGE_NODE}",#' /root/iRedMail-0.8.6/samples/iredmail.mysql
+ cat
+ ECHO_DEBUG 'Import postfix virtual hosts/users: /root/iRedMail-0.8.6/conf/mysql_vmail.sql.'
+ '[' XNO == XYES ']'
+ :
+ mysql --defaults-file=/root/iRedMail-0.8.6/.mysql-root-defaults-file
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)
+ cat
+ echo 'export status_mysql_import_vmail_users="DONE"'
+ set +x
< INFO > Configure Postfix (Message Transfer Agent).
< INFO > Configure Cluebringer (postfix policy server).
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)
< INFO > Configure Dovecot-2 (pop3/imap/managesieve server).
< INFO > Configure ClamAV (anti-virus toolkit).
< INFO > Configure Amavisd-new (interface between MTA and content checkers).
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)
< INFO > Configure SpamAssassin (content-based spam filter).
< INFO > Configure iRedAPD (postfix policy daemon).
< INFO > Configure iRedAdmin (official web-based admin panel).
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)
< INFO > Configure Fail2ban (authentication failure monitor).
< INFO > Configure Awstats (logfile analyzer for mail and web server).
< INFO > Configure Roundcube webmail.
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)
< INFO > Configure phpMyAdmin (web-based MySQL management tool).

*************************************************************************
* iRedMail-0.8.6 installation and configuration complete.
*************************************************************************

< INFO > Mail sensitive administration info to postmaster@XXXXXXXX.

Should I open this in a separate thread since it's a slightly (different distro) issue? I didn't want to clutter the forum too much.