ctwm: 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 Debian possible default full paths are:

/usr/bin/ctwm - from package: ctwm

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

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