dumpcap: 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/sbin/dumpcap - from package: wireshark

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

On Debian possible default full paths are:

/usr/bin/dumpcap - from package: wireshark-common

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

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