relpath-2.6.4: 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/bin/relpath-2.6.4 - from package: fp-utils-2.6.4

You may install the required package with command apt-get install {package}
Error in other languages:
relpath-2.6.4: bevel nie gevind nie
relpath-2.6.4: comandă negăsită
relpath-2.6.4: comando não encontrado
relpath-2.6.4: commande introuvable
relpath-2.6.4: command not found
relpath-2.6.4: käsku ei ole
relpath-2.6.4: không tìm thấy lệnh
relpath-2.6.4: komanda nerasta
relpath-2.6.4: Kommando nicht gefunden.
relpath-2.6.4: kommandot finns inte
relpath-2.6.4: komut yok
relpath-2.6.4: nie znaleziono polecenia
relpath-2.6.4: níor aimsíodh an t-ordú
relpath-2.6.4: no se encontró la orden
relpath-2.6.4: no s'ha trobat l'ordre
relpath-2.6.4: opdracht niet gevonden
relpath-2.6.4: parancs nem található
relpath-2.6.4: perintah tidak ditemukan
relpath-2.6.4: príkaz nenájdený
relpath-2.6.4: příkaz nenalezen
relpath-2.6.4: команда не найдена
relpath-2.6.4: командата не е открита
relpath-2.6.4: 命令找不到
relpath-2.6.4: コマンドが見つかりません