apcupsd: 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:

/sbin/apcupsd - from package: apcupsd

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

On Debian possible default full paths are:

/sbin/apcupsd - from package: apcupsd

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

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