ppm2video: 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/ppm2video - from package: gerris-mpi
/usr/bin/ppm2video - from package: gerris

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

Error in other languages:
ppm2video: bevel nie gevind nie
ppm2video: comandă negăsită
ppm2video: comando não encontrado
ppm2video: commande introuvable
ppm2video: command not found
ppm2video: käsku ei ole
ppm2video: không tìm thấy lệnh
ppm2video: komanda nerasta
ppm2video: Kommando nicht gefunden.
ppm2video: kommandot finns inte
ppm2video: komut yok
ppm2video: nie znaleziono polecenia
ppm2video: níor aimsíodh an t-ordú
ppm2video: no se encontró la orden
ppm2video: no s'ha trobat l'ordre
ppm2video: opdracht niet gevonden
ppm2video: parancs nem található
ppm2video: perintah tidak ditemukan
ppm2video: príkaz nenájdený
ppm2video: příkaz nenalezen
ppm2video: команда не найдена
ppm2video: командата не е открита
ppm2video: 命令找不到
ppm2video: コマンドが見つかりません