xfs_quota: 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/xfs_quota - from package: xfsprogs

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

On Debian possible default full paths are:

/usr/sbin/xfs_quota - from package: xfsprogs

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

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