ppm2theora: 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/ppm2theora - from package: gerris-mpi
/usr/bin/ppm2theora - from package: gerris

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

Error in other languages:
ppm2theora: bevel nie gevind nie
ppm2theora: comandă negăsită
ppm2theora: comando não encontrado
ppm2theora: commande introuvable
ppm2theora: command not found
ppm2theora: käsku ei ole
ppm2theora: không tìm thấy lệnh
ppm2theora: komanda nerasta
ppm2theora: Kommando nicht gefunden.
ppm2theora: kommandot finns inte
ppm2theora: komut yok
ppm2theora: nie znaleziono polecenia
ppm2theora: níor aimsíodh an t-ordú
ppm2theora: no se encontró la orden
ppm2theora: no s'ha trobat l'ordre
ppm2theora: opdracht niet gevonden
ppm2theora: parancs nem található
ppm2theora: perintah tidak ditemukan
ppm2theora: príkaz nenájdený
ppm2theora: příkaz nenalezen
ppm2theora: команда не найдена
ppm2theora: командата не е открита
ppm2theora: 命令找不到
ppm2theora: コマンドが見つかりません