graphchk64: 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/graphchk64 - from package: metis64

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

Error in other languages:
graphchk64: bevel nie gevind nie
graphchk64: comandă negăsită
graphchk64: comando não encontrado
graphchk64: commande introuvable
graphchk64: command not found
graphchk64: käsku ei ole
graphchk64: không tìm thấy lệnh
graphchk64: komanda nerasta
graphchk64: Kommando nicht gefunden.
graphchk64: kommandot finns inte
graphchk64: komut yok
graphchk64: nie znaleziono polecenia
graphchk64: níor aimsíodh an t-ordú
graphchk64: no se encontró la orden
graphchk64: no s'ha trobat l'ordre
graphchk64: opdracht niet gevonden
graphchk64: parancs nem található
graphchk64: perintah tidak ditemukan
graphchk64: príkaz nenájdený
graphchk64: příkaz nenalezen
graphchk64: команда не найдена
graphchk64: командата не е открита
graphchk64: 命令找不到
graphchk64: コマンドが見つかりません