nycheck-gfortran: 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/nycheck-gfortran - from package: patchy-gfortran

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

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