pgmnoise: 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/pgmnoise - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pgmnoise - from package: netpbm

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

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