tuned-adm: 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/tuned-adm - from package: tuned
/usr/sbin/tuned-adm - from package: tuned

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

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