mymd5sum: 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/mymd5sum - from package: atlc

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

Error in other languages:
mymd5sum: bevel nie gevind nie
mymd5sum: comandă negăsită
mymd5sum: comando não encontrado
mymd5sum: commande introuvable
mymd5sum: command not found
mymd5sum: käsku ei ole
mymd5sum: không tìm thấy lệnh
mymd5sum: komanda nerasta
mymd5sum: Kommando nicht gefunden.
mymd5sum: kommandot finns inte
mymd5sum: komut yok
mymd5sum: nie znaleziono polecenia
mymd5sum: níor aimsíodh an t-ordú
mymd5sum: no se encontró la orden
mymd5sum: no s'ha trobat l'ordre
mymd5sum: opdracht niet gevonden
mymd5sum: parancs nem található
mymd5sum: perintah tidak ditemukan
mymd5sum: príkaz nenájdený
mymd5sum: příkaz nenalezen
mymd5sum: команда не найдена
mymd5sum: командата не е открита
mymd5sum: 命令找不到
mymd5sum: コマンドが見つかりません