parallel-rsync: 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/parallel-rsync - from package: pssh

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

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