unbound-checkconf: 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/sbin/unbound-checkconf - from package: unbound

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

On Debian possible default full paths are:

/usr/sbin/unbound-checkconf - from package: unbound

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

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