manage_exports: 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/bin/manage_exports - from package: nfs-ganesha-utils

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

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