gnome-system-log-pkexec: 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 Debian possible default full paths are:

/usr/bin/gnome-system-log-pkexec - from package: gnome-system-log

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

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