swapoff: 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/swapoff - from package: util-linux-ng

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

On Debian possible default full paths are:

/sbin/swapoff - from package: mount

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

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