mpicxx.openmpi: 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/mpicxx.openmpi - from package: libopenmpi-dev

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

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