linux64: 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/linux64 - from package: util-linux-ng

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

On Debian possible default full paths are:

/usr/bin/linux64 - from package: util-linux

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

Error in other languages:
linux64: bevel nie gevind nie
linux64: comandă negăsită
linux64: comando não encontrado
linux64: commande introuvable
linux64: command not found
linux64: käsku ei ole
linux64: không tìm thấy lệnh
linux64: komanda nerasta
linux64: Kommando nicht gefunden.
linux64: kommandot finns inte
linux64: komut yok
linux64: nie znaleziono polecenia
linux64: níor aimsíodh an t-ordú
linux64: no se encontró la orden
linux64: no s'ha trobat l'ordre
linux64: opdracht niet gevonden
linux64: parancs nem található
linux64: perintah tidak ditemukan
linux64: príkaz nenájdený
linux64: příkaz nenalezen
linux64: команда не найдена
linux64: командата не е открита
linux64: 命令找不到
linux64: コマンドが見つかりません