fitsort: 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/fitsort - from package: qfits-tools

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

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