pkcheck: 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/pkcheck - from package: polkit

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

On Debian possible default full paths are:

/usr/bin/pkcheck - from package: policykit-1

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

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