مشکل gnome-flashback

[tempel]

سلام. برای نصب میزکارclassic ابتدا با دستور

 
 sudo apt update

مخازن رو بروزرسانی(ولی روبروی تعدادی از خط ها نوشته some index failed to download) و با

 
 sudo apt-get install gnome-session-flashback

باید میزکارو نصب کنه ولی این خطارو میده

 
 Reading package lists... Done Building dependency tree        Reading state information... Done Package gnome-session-flashback is not available, but is referred to by another package. This may mean that the package is missing, has been obsoleted, or is only available from another source  E: Package 'gnome-session-flashback' has no installation candidate

به نظرتون مشکل کجاست