I thank you all for your help. But there seems to be a big misunderstanding.
The issue is not how to use sudo or how to set up no-password. If you could see my original report, it would be clear. But it seems to have fallen off the thread. Here is what happened. $sudo apt-get install flashplugin-nonfree then I typed my password. ----- ERROR: wget failed to download http://people.debian.org/~bartm/flashplugin-nonfree/fp10.sha512.amd64.pgp.asc More information might be available at: http://wiki.debian.org/FlashPlayer I checked the following $ LANG="en_US.utf8" wget -v http://people.debian.org/~bartm/flashplugin-nonfree/fp10.sha512.amd64.pgp.asc --2012-04-30<http://people.debian.org/%7Ebartm/flashplugin-nonfree/fp10.sha512.amd64.pgp.asc--2012-04-30>14:42:43-- http://people.debian.org/~bartm/flashplugin-nonfree/fp10.sha512.amd64.pgp.asc Resolving ns14... 10.1.1.12 Connecting to ns14|10.1.1.12|:8080... connected. Proxy request sent, awaiting response... 200 OK Length: 1273 (1.2K) [text/plain] fp10.sha512.amd64.pgp.asc: Permission denied Next, I did this $su Then I typed my password # apt-get install flashplugin-nonfree And it succeeded. So, it seems that when I invoked the command under sudo, the script invoked by the command tried to write a file to a directory, but failed because of denied permission. But when I invoked it under superuser, it succeeded. So, I wonder whether this is because (1) I mishandled my set up of sudo (2) this is a subtle bug of packaging of flashplugin-nonfree, (3) this is a feature of flashplugin-nonfree package unavoidable for some security reason (4) Debian culture commands that I become superuser instead of using sudo. Cheers, Han Soo
