pcapdump: 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/pcapdump - from package: pcaputils

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

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