msgsnarf: 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/msgsnarf - from package: dsniff

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

On Debian possible default full paths are:

/usr/sbin/msgsnarf - from package: dsniff

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

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