quota: command not found

Have You tried accessing the binary with the full path?

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/quota - from package: quota

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

On Debian possible default full paths are:

/usr/bin/quota - from package: quota
/usr/lib/cyrus/bin/quota - from package: cyrus-common

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