apt-mark: 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/apt-mark - from package: apt

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

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