spice-vdagent: 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/spice-vdagent - from package: spice-vdagent

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

On Debian possible default full paths are:

/usr/bin/spice-vdagent - from package: spice-vdagent

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

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