stxxl_tool: 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/stxxl_tool - from package: libstxxl1-bin

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

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