xr: 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/xr - from package: crossroads

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

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