arc: 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/arc - from package: arc

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

On Debian possible default full paths are:

/usr/bin/arc - from package: arc

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

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