xastir_udp_client: 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/xastir_udp_client - from package: xastir

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

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