mate-screenshot: 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/mate-screenshot - from package: mate-utils

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

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