rib_show_distances: 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

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/rib_show_distances - from package: xorp

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