lttng-relayd: 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/lttng-relayd - from package: lttng-tools

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

On Debian possible default full paths are:

/usr/bin/lttng-relayd - from package: lttng-tools

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

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