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

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

On Debian possible default full paths are:

/sbin/losetup - from package: mount
/usr/lib/klibc/bin/losetup - from package: klibc-utils

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

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