randicmp6: 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/randicmp6 - from package: thc-ipv6

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

Error in other languages:
randicmp6: bevel nie gevind nie
randicmp6: comandă negăsită
randicmp6: comando não encontrado
randicmp6: commande introuvable
randicmp6: command not found
randicmp6: käsku ei ole
randicmp6: không tìm thấy lệnh
randicmp6: komanda nerasta
randicmp6: Kommando nicht gefunden.
randicmp6: kommandot finns inte
randicmp6: komut yok
randicmp6: nie znaleziono polecenia
randicmp6: níor aimsíodh an t-ordú
randicmp6: no se encontró la orden
randicmp6: no s'ha trobat l'ordre
randicmp6: opdracht niet gevonden
randicmp6: parancs nem található
randicmp6: perintah tidak ditemukan
randicmp6: príkaz nenájdený
randicmp6: příkaz nenalezen
randicmp6: команда не найдена
randicmp6: командата не е открита
randicmp6: 命令找不到
randicmp6: コマンドが見つかりません