blkls: 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/blkls - from package: sleuthkit

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

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