libwebsockets-test-ping: 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:

/usr/bin/libwebsockets-test-ping - from package: libwebsockets-test-server

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

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