quotaon: 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:

/sbin/quotaon - from package: quota

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

On Debian possible default full paths are:

/sbin/quotaon - from package: quota

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

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