rsaperf: 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 Debian possible default full paths are:

/usr/bin/rsaperf - from package: libnss3-tools

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

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