guacd: 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/sbin/guacd - from package: guacd

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

On Debian possible default full paths are:

/usr/sbin/guacd - from package: guacd

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

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