lskrf: 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/lskrf - from package: dnssec-tools

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

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