ompi-top: command not found

Have You tried accessing the binary with the full path?

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/ompi-top - from package: openmpi-bin

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