ga-config: 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/lib64/mpich/bin/ga-config - from package: ga-mpich-devel
/usr/lib/mpich/bin/ga-config - from package: ga-mpich-devel
/usr/lib64/openmpi/bin/ga-config - from package: ga-openmpi-devel
/usr/lib/openmpi/bin/ga-config - from package: ga-openmpi-devel

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

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