rrenice: 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/rrenice - from package: pslist

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

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