chkwtmp: 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/sbin/chkwtmp - from package: chkrootkit

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

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