curvecpserver: 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/curvecpserver - from package: nacl

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

On Debian possible default full paths are:

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

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

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