uml_mkcow: 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/uml_mkcow - from package: uml_utilities

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

On Debian possible default full paths are:

/usr/bin/uml_mkcow - from package: uml-utilities

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

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