whatmask: 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/whatmask - from package: whatmask

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

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