v.kcv: 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/v.kcv - 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.kcv - from package: grass-core

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

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