ipv6logconv: 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/ipv6logconv - from package: ipv6calc

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

On Debian possible default full paths are:

/usr/bin/ipv6logconv - from package: ipv6calc

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

Error in other languages:
ipv6logconv: bevel nie gevind nie
ipv6logconv: comandă negăsită
ipv6logconv: comando não encontrado
ipv6logconv: commande introuvable
ipv6logconv: command not found
ipv6logconv: käsku ei ole
ipv6logconv: không tìm thấy lệnh
ipv6logconv: komanda nerasta
ipv6logconv: Kommando nicht gefunden.
ipv6logconv: kommandot finns inte
ipv6logconv: komut yok
ipv6logconv: nie znaleziono polecenia
ipv6logconv: níor aimsíodh an t-ordú
ipv6logconv: no se encontró la orden
ipv6logconv: no s'ha trobat l'ordre
ipv6logconv: opdracht niet gevonden
ipv6logconv: parancs nem található
ipv6logconv: perintah tidak ditemukan
ipv6logconv: príkaz nenájdený
ipv6logconv: příkaz nenalezen
ipv6logconv: команда не найдена
ipv6logconv: командата не е открита
ipv6logconv: 命令找不到
ipv6logconv: コマンドが見つかりません