ct: 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/ct - from package: mgetty-sendfax

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

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