knife: 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 Debian possible default full paths are:

/usr/bin/knife - from package: chef

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

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