ramdisk-image-create: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/ramdisk-image-create - from package: diskimage-builder

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

On Debian possible default full paths are:

/usr/bin/ramdisk-image-create - from package: python-diskimage-builder

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