alsamixergui: 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/alsamixergui - from package: alsamixergui

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

On Debian possible default full paths are:

/usr/bin/alsamixergui - from package: alsamixergui

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

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