mate-about: 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-about - from package: mate-desktop

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

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