isfits: 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/isfits - from package: wcstools

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

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