mpif77: 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 CentOS possible default full paths are:

/usr/bin/mpif77 - from package: mpich2-devel
/usr/lib64/mpich2/bin/mpif77 - from package: mpich2-devel
/usr/lib/mpich2/bin/mpif77 - from package: mpich2-devel
/usr/lib64/mpich/bin/mpif77 - from package: mpich-devel
/usr/lib/mpich/bin/mpif77 - from package: mpich-devel
/usr/lib64/mvapich2/bin/mpif77 - from package: mvapich2-devel
/usr/lib/mvapich2/bin/mpif77 - from package: mvapich2-devel
/usr/lib64/mvapich2-psm/bin/mpif77 - from package: mvapich2-psm-devel

You may install the required package with command yum install {package}

Error in other languages:
mpif77: bevel nie gevind nie
mpif77: comandă negăsită
mpif77: comando não encontrado
mpif77: commande introuvable
mpif77: command not found
mpif77: käsku ei ole
mpif77: không tìm thấy lệnh
mpif77: komanda nerasta
mpif77: Kommando nicht gefunden.
mpif77: kommandot finns inte
mpif77: komut yok
mpif77: nie znaleziono polecenia
mpif77: níor aimsíodh an t-ordú
mpif77: no se encontró la orden
mpif77: no s'ha trobat l'ordre
mpif77: opdracht niet gevonden
mpif77: parancs nem található
mpif77: perintah tidak ditemukan
mpif77: príkaz nenájdený
mpif77: příkaz nenalezen
mpif77: команда не найдена
mpif77: командата не е открита
mpif77: 命令找不到
mpif77: コマンドが見つかりません