yum-arch: 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/yum-arch - from package: yum-arch

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

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