kvirc: 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/bin/kvirc - from package: kvirc

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

On Debian possible default full paths are:

/usr/bin/kvirc - from package: kvirc

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

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