blkcalc: 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/blkcalc - from package: sleuthkit

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

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