unbound-anchor: 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-anchor - from package: unbound-libs

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

On Debian possible default full paths are:

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

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

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