qemu-ga: 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-ga - from package: qemu-guest-agent

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

On Debian possible default full paths are:

/usr/sbin/qemu-ga - from package: qemu-guest-agent

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

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