font-sampler: command not found

Have You tried accessing the binary with the full path?

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/font-sampler - from package: font-manager

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