cygdb3: 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/cygdb3 - from package: cython3

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

Error in other languages:
cygdb3: bevel nie gevind nie
cygdb3: comandă negăsită
cygdb3: comando não encontrado
cygdb3: commande introuvable
cygdb3: command not found
cygdb3: käsku ei ole
cygdb3: không tìm thấy lệnh
cygdb3: komanda nerasta
cygdb3: Kommando nicht gefunden.
cygdb3: kommandot finns inte
cygdb3: komut yok
cygdb3: nie znaleziono polecenia
cygdb3: níor aimsíodh an t-ordú
cygdb3: no se encontró la orden
cygdb3: no s'ha trobat l'ordre
cygdb3: opdracht niet gevonden
cygdb3: parancs nem található
cygdb3: perintah tidak ditemukan
cygdb3: príkaz nenájdený
cygdb3: příkaz nenalezen
cygdb3: команда не найдена
cygdb3: командата не е открита
cygdb3: 命令找不到
cygdb3: コマンドが見つかりません