acpi_available: 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:

/sbin/acpi_available - from package: powermgmt-base

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

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