visitors: 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/visitors - from package: visitors

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

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