d.rhumbline: 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 CentOS possible default full paths are:

/usr/lib64/grass-6.4.4/bin/d.rhumbline - from package: grass

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/lib/grass64/bin/d.rhumbline - from package: grass-core

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

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