mate-cpufreq-selector: 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-cpufreq-selector - from package: mate-applets

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

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