fols: 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/share/doc/mh-book/examples/mh/bin/fols - from package: mh-book

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

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