nib-nifti-dx: 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/nib-nifti-dx - from package: python-nibabel

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

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