ctangle: 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/ctangle - from package: texlive

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

On Debian possible default full paths are:

/usr/bin/ctangle - from package: texlive-binaries

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

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