mpif90.mpich: 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/mpif90.mpich - from package: libmpich-dev

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

Error in other languages:
mpif90.mpich: bevel nie gevind nie
mpif90.mpich: comandă negăsită
mpif90.mpich: comando não encontrado
mpif90.mpich: commande introuvable
mpif90.mpich: command not found
mpif90.mpich: käsku ei ole
mpif90.mpich: không tìm thấy lệnh
mpif90.mpich: komanda nerasta
mpif90.mpich: Kommando nicht gefunden.
mpif90.mpich: kommandot finns inte
mpif90.mpich: komut yok
mpif90.mpich: nie znaleziono polecenia
mpif90.mpich: níor aimsíodh an t-ordú
mpif90.mpich: no se encontró la orden
mpif90.mpich: no s'ha trobat l'ordre
mpif90.mpich: opdracht niet gevonden
mpif90.mpich: parancs nem található
mpif90.mpich: perintah tidak ditemukan
mpif90.mpich: príkaz nenájdený
mpif90.mpich: příkaz nenalezen
mpif90.mpich: команда не найдена
mpif90.mpich: командата не е открита
mpif90.mpich: 命令找不到
mpif90.mpich: コマンドが見つかりません