addr2name: 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/addr2name - from package: ndisc6

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

On Debian possible default full paths are:

/usr/bin/addr2name - from package: ndisc6

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

Error in other languages:
addr2name: bevel nie gevind nie
addr2name: comandă negăsită
addr2name: comando não encontrado
addr2name: commande introuvable
addr2name: command not found
addr2name: käsku ei ole
addr2name: không tìm thấy lệnh
addr2name: komanda nerasta
addr2name: Kommando nicht gefunden.
addr2name: kommandot finns inte
addr2name: komut yok
addr2name: nie znaleziono polecenia
addr2name: níor aimsíodh an t-ordú
addr2name: no se encontró la orden
addr2name: no s'ha trobat l'ordre
addr2name: opdracht niet gevonden
addr2name: parancs nem található
addr2name: perintah tidak ditemukan
addr2name: príkaz nenájdený
addr2name: příkaz nenalezen
addr2name: команда не найдена
addr2name: командата не е открита
addr2name: 命令找不到
addr2name: コマンドが見つかりません