sniff: 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/bin/sniff - from package: dogtail

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

On Debian possible default full paths are:

/usr/bin/sniff - from package: python-dogtail

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

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