st4topgm: 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/st4topgm - from package: netpbm

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

Error in other languages:
st4topgm: bevel nie gevind nie
st4topgm: comandă negăsită
st4topgm: comando não encontrado
st4topgm: commande introuvable
st4topgm: command not found
st4topgm: käsku ei ole
st4topgm: không tìm thấy lệnh
st4topgm: komanda nerasta
st4topgm: Kommando nicht gefunden.
st4topgm: kommandot finns inte
st4topgm: komut yok
st4topgm: nie znaleziono polecenia
st4topgm: níor aimsíodh an t-ordú
st4topgm: no se encontró la orden
st4topgm: no s'ha trobat l'ordre
st4topgm: opdracht niet gevonden
st4topgm: parancs nem található
st4topgm: perintah tidak ditemukan
st4topgm: príkaz nenájdený
st4topgm: příkaz nenalezen
st4topgm: команда не найдена
st4topgm: командата не е открита
st4topgm: 命令找不到
st4topgm: コマンドが見つかりません