prefetch: 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/prefetch - from package: sra-toolkit

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

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