jdb: 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/lib/jvm/java-1.5.0-gcj-4.8-amd64/bin/jdb - from package: gcj-4.8-jdk
/usr/lib/jvm/java-1.5.0-gcj-4.9-amd64/bin/jdb - from package: gcj-4.9-jdk
/usr/lib/debug/usr/lib/jvm/java-7-openjdk-amd64/bin/jdb - from package: openjdk-7-dbg
/usr/lib/jvm/java-7-openjdk-amd64/bin/jdb - from package: openjdk-7-jdk

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

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