qemu-img: 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/bin/qemu-img - from package: qemu-img

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

On Debian possible default full paths are:

/usr/bin/qemu-img - from package: qemu-utils

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

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