nacl-sha512: 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/nacl-sha512 - from package: nacl

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

On Debian possible default full paths are:

/usr/bin/nacl-sha512 - from package: nacl-tools

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

Error in other languages:
nacl-sha512: bevel nie gevind nie
nacl-sha512: comandă negăsită
nacl-sha512: comando não encontrado
nacl-sha512: commande introuvable
nacl-sha512: command not found
nacl-sha512: käsku ei ole
nacl-sha512: không tìm thấy lệnh
nacl-sha512: komanda nerasta
nacl-sha512: Kommando nicht gefunden.
nacl-sha512: kommandot finns inte
nacl-sha512: komut yok
nacl-sha512: nie znaleziono polecenia
nacl-sha512: níor aimsíodh an t-ordú
nacl-sha512: no se encontró la orden
nacl-sha512: no s'ha trobat l'ordre
nacl-sha512: opdracht niet gevonden
nacl-sha512: parancs nem található
nacl-sha512: perintah tidak ditemukan
nacl-sha512: príkaz nenájdený
nacl-sha512: příkaz nenalezen
nacl-sha512: команда не найдена
nacl-sha512: командата не е открита
nacl-sha512: 命令找不到
nacl-sha512: コマンドが見つかりません