convertquota: 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/convertquota - from package: quota

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

On Debian possible default full paths are:

/usr/sbin/convertquota - from package: quota

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

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