pure-authd: 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/pure-authd - from package: pure-ftpd

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

On Debian possible default full paths are:

/usr/sbin/pure-authd - from package: pure-ftpd-ldap
/usr/sbin/pure-authd - from package: pure-ftpd-mysql
/usr/sbin/pure-authd - from package: pure-ftpd-postgresql
/usr/sbin/pure-authd - from package: pure-ftpd

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

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