cpufreq-set: 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 CentOS possible default full paths are:

/usr/bin/cpufreq-set - from package: cpufrequtils

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/cpufreq-set - from package: cpufrequtils

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

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