gem2rpm: 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/gem2rpm - from package: rubygem-gem2rpm
/usr/lib/ruby/gems/1.8/gems/gem2rpm-0.11.3/bin/gem2rpm - from package: rubygem-gem2rpm

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

Error in other languages:
gem2rpm: bevel nie gevind nie
gem2rpm: comandă negăsită
gem2rpm: comando não encontrado
gem2rpm: commande introuvable
gem2rpm: command not found
gem2rpm: käsku ei ole
gem2rpm: không tìm thấy lệnh
gem2rpm: komanda nerasta
gem2rpm: Kommando nicht gefunden.
gem2rpm: kommandot finns inte
gem2rpm: komut yok
gem2rpm: nie znaleziono polecenia
gem2rpm: níor aimsíodh an t-ordú
gem2rpm: no se encontró la orden
gem2rpm: no s'ha trobat l'ordre
gem2rpm: opdracht niet gevonden
gem2rpm: parancs nem található
gem2rpm: perintah tidak ditemukan
gem2rpm: príkaz nenájdený
gem2rpm: příkaz nenalezen
gem2rpm: команда не найдена
gem2rpm: командата не е открита
gem2rpm: 命令找不到
gem2rpm: コマンドが見つかりません