pki-server: 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
/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/pki-server - from package: pki-common

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