411toppm: 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 CentOS possible default full paths are:

/usr/bin/411toppm - from package: netpbm-progs

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/411toppm - from package: netpbm

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

Error in other languages:
411toppm: bevel nie gevind nie
411toppm: comandă negăsită
411toppm: comando não encontrado
411toppm: commande introuvable
411toppm: command not found
411toppm: käsku ei ole
411toppm: không tìm thấy lệnh
411toppm: komanda nerasta
411toppm: Kommando nicht gefunden.
411toppm: kommandot finns inte
411toppm: komut yok
411toppm: nie znaleziono polecenia
411toppm: níor aimsíodh an t-ordú
411toppm: no se encontró la orden
411toppm: no s'ha trobat l'ordre
411toppm: opdracht niet gevonden
411toppm: parancs nem található
411toppm: perintah tidak ditemukan
411toppm: príkaz nenájdený
411toppm: příkaz nenalezen
411toppm: команда не найдена
411toppm: командата не е открита
411toppm: 命令找不到
411toppm: コマンドが見つかりません