fea_show_interfaces: command not found

Have You tried accessing the binary with the full path?

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/lib/xorp/bin/fea_show_interfaces - from package: xorp

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