knotc: 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/sbin/knotc - from package: knot

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

On Debian possible default full paths are:

/usr/sbin/knotc - from package: knot

You may install the required package with command apt-get install {package}

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