sha256: 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/sbin/sha256 - from package: hashalot

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

Error in other languages:
sha256: bevel nie gevind nie
sha256: comandă negăsită
sha256: comando não encontrado
sha256: commande introuvable
sha256: command not found
sha256: käsku ei ole
sha256: không tìm thấy lệnh
sha256: komanda nerasta
sha256: Kommando nicht gefunden.
sha256: kommandot finns inte
sha256: komut yok
sha256: nie znaleziono polecenia
sha256: níor aimsíodh an t-ordú
sha256: no se encontró la orden
sha256: no s'ha trobat l'ordre
sha256: opdracht niet gevonden
sha256: parancs nem található
sha256: perintah tidak ditemukan
sha256: príkaz nenájdený
sha256: příkaz nenalezen
sha256: команда не найдена
sha256: командата не е открита
sha256: 命令找不到
sha256: コマンドが見つかりません