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

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

Error in other languages:
g77: bevel nie gevind nie
g77: comandă negăsită
g77: comando não encontrado
g77: commande introuvable
g77: command not found
g77: käsku ei ole
g77: không tìm thấy lệnh
g77: komanda nerasta
g77: Kommando nicht gefunden.
g77: kommandot finns inte
g77: komut yok
g77: nie znaleziono polecenia
g77: níor aimsíodh an t-ordú
g77: no se encontró la orden
g77: no s'ha trobat l'ordre
g77: opdracht niet gevonden
g77: parancs nem található
g77: perintah tidak ditemukan
g77: príkaz nenájdený
g77: příkaz nenalezen
g77: команда не найдена
g77: командата не е открита
g77: 命令找不到
g77: コマンドが見つかりません