chklastlog: command not found

Have You tried accessing the binary with the full path?

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/chklastlog - from package: chkrootkit

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