tsk_recover: 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/tsk_recover - from package: sleuthkit

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

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