v.label.sa: 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 CentOS possible default full paths are:

/usr/lib64/grass-6.4.4/bin/v.label.sa - 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/v.label.sa - from package: grass-core

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