unbound-streamtcp: 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

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-streamtcp - from package: unbound

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