grib2ppm: 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/grib2ppm - from package: grib_api

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

On Debian possible default full paths are:

/usr/bin/grib2ppm - from package: libgrib-api-tools

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

Error in other languages:
grib2ppm: bevel nie gevind nie
grib2ppm: comandă negăsită
grib2ppm: comando não encontrado
grib2ppm: commande introuvable
grib2ppm: command not found
grib2ppm: käsku ei ole
grib2ppm: không tìm thấy lệnh
grib2ppm: komanda nerasta
grib2ppm: Kommando nicht gefunden.
grib2ppm: kommandot finns inte
grib2ppm: komut yok
grib2ppm: nie znaleziono polecenia
grib2ppm: níor aimsíodh an t-ordú
grib2ppm: no se encontró la orden
grib2ppm: no s'ha trobat l'ordre
grib2ppm: opdracht niet gevonden
grib2ppm: parancs nem található
grib2ppm: perintah tidak ditemukan
grib2ppm: príkaz nenájdený
grib2ppm: příkaz nenalezen
grib2ppm: команда не найдена
grib2ppm: командата не е открита
grib2ppm: 命令找不到
grib2ppm: コマンドが見つかりません