f77: 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/f77 - from package: compat-gcc-34-g77

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

Error in other languages:
f77: bevel nie gevind nie
f77: comandă negăsită
f77: comando não encontrado
f77: commande introuvable
f77: command not found
f77: käsku ei ole
f77: không tìm thấy lệnh
f77: komanda nerasta
f77: Kommando nicht gefunden.
f77: kommandot finns inte
f77: komut yok
f77: nie znaleziono polecenia
f77: níor aimsíodh an t-ordú
f77: no se encontró la orden
f77: no s'ha trobat l'ordre
f77: opdracht niet gevonden
f77: parancs nem található
f77: perintah tidak ditemukan
f77: príkaz nenájdený
f77: příkaz nenalezen
f77: команда не найдена
f77: командата не е открита
f77: 命令找不到
f77: コマンドが見つかりません