$ cd /usr/share/xsessions/
jlg@UL30A:/usr/share/xsessions$ ls
lightdm-xsession.desktop xfce.desktop
jlg@UL30A:/usr/share/xsessions$ cat lightdm-xsession.desktop
[Desktop Entry]
Version=1.0
Name=Default Xsession
Exec=default
Icon=
Type=Application
jlg@UL30A:/usr/share/xsessions$ cp lightdm-xsession.desktop lightdm-xsession.desktop_old
cp: impossible de créer le fichier standard « lightdm-xsession.desktop_old »: Permission non accordée
jlg@UL30A:/usr/share/xsessions$ sudo cp lightdm-xsession.desktop lightdm-xsession.desktop_old
[sudo] password for jlg:
jlg@UL30A:/usr/share/xsessions$ ls
lightdm-xsession.desktop lightdm-xsession.desktop_old xfce.desktop
jlg@UL30A:/usr/share/xsessions$ sudo mousepad lightdm-xsession.desktop
jlg@UL30A:/usr/share/xsessions$ cat lightdm-xsession.desktop
[Desktop Entry]
Version=1.0
Name=Xfce Xsession
Exec=startxfce4
Icon=
Type=Application
jlg@UL30A:/usr/share/xsessions$