fitsmd5: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/fitsmd5 - from package: qfits-tools

You may install the required package with command apt-get install {package}
Error in other languages:
fitsmd5: bevel nie gevind nie
fitsmd5: comandă negăsită
fitsmd5: comando não encontrado
fitsmd5: commande introuvable
fitsmd5: command not found
fitsmd5: käsku ei ole
fitsmd5: không tìm thấy lệnh
fitsmd5: komanda nerasta
fitsmd5: Kommando nicht gefunden.
fitsmd5: kommandot finns inte
fitsmd5: komut yok
fitsmd5: nie znaleziono polecenia
fitsmd5: níor aimsíodh an t-ordú
fitsmd5: no se encontró la orden
fitsmd5: no s'ha trobat l'ordre
fitsmd5: opdracht niet gevonden
fitsmd5: parancs nem található
fitsmd5: perintah tidak ditemukan
fitsmd5: príkaz nenájdený
fitsmd5: příkaz nenalezen
fitsmd5: команда не найдена
fitsmd5: командата не е открита
fitsmd5: 命令找不到
fitsmd5: コマンドが見つかりません