zabbix_server: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/sbin/zabbix_server - from package: zabbix20-server
/usr/sbin/zabbix_server - from package: zabbix22-server

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/sbin/zabbix_server - from package: zabbix-server-mysql
/usr/sbin/zabbix_server - from package: zabbix-server-pgsql

You may install the required package with command apt-get install {package}

Error in other languages:
zabbix_server: bevel nie gevind nie
zabbix_server: comandă negăsită
zabbix_server: comando não encontrado
zabbix_server: commande introuvable
zabbix_server: command not found
zabbix_server: käsku ei ole
zabbix_server: không tìm thấy lệnh
zabbix_server: komanda nerasta
zabbix_server: Kommando nicht gefunden.
zabbix_server: kommandot finns inte
zabbix_server: komut yok
zabbix_server: nie znaleziono polecenia
zabbix_server: níor aimsíodh an t-ordú
zabbix_server: no se encontró la orden
zabbix_server: no s'ha trobat l'ordre
zabbix_server: opdracht niet gevonden
zabbix_server: parancs nem található
zabbix_server: perintah tidak ditemukan
zabbix_server: príkaz nenájdený
zabbix_server: příkaz nenalezen
zabbix_server: команда не найдена
zabbix_server: командата не е открита
zabbix_server: 命令找不到
zabbix_server: コマンドが見つかりません