r.basins.fill: 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 CentOS possible default full paths are:

/usr/lib64/grass-6.4.4/bin/r.basins.fill - 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/r.basins.fill - from package: grass-core

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