My Update Manager says my system is out of date but when I click "Check", it comes back that repositories are missing or damaged.

Just remove the repository. It is a 3rd party repo you have added. Changing server only affects the official repos so will do nothing to this at all.

open your software sources and simply remove the entrys for the repo you are having issue with. You can now update / upgrade cleanly.

I've gone in and unchk'd all the updates and/or upgrades that added repositories to the Upgrade Manager, until I realized there was a "Revert" button at the bottom of the screens .. duh ... Anyway, they're all grayed out now, which I'll assume means it's back to the default settings.

I've done several chks and nothing's changed. However, not knowing if it'll help or not, here's the "title" of the screen which shows the above posting:

"Could not download all repository indexes

The repository may no longer be available or could not be contacted because of network problems. If available an older version of the failed index will be used. Otherwise the repository will be ignored. Check your network connection and ensure the repository address in the preferences is correct."

My son told me that a few lines in my source.list file in /etc/apt dir were wrong. He rewrote the file for me but now I can't figure out how to rewrite the file. Obviously not through gedit but I can't figure out how to do the following in a terminal window: create a file, name it source.list and tell the system to overwrite the existing file.

If this is the right way to do it, in my Ubuntu 10.04 LTS, then pls tell me HOW to do it.

If it's NOT the right way (it's what I would've done in DOS lo, these many years), can someone tell me what to do?

He's off work for the weekend and I won't be able to reach him. And he runs servers at a server farm so I know he knows his Linux. But most of you know what it's like when the kids know more than the parents ...

Help please?

I figured out how to "re-do" the source.list file.

Here's how my son's edited source.list file looks like:

#
# deb cdrom:[Ubuntu 10.04.1 LTS _Lucid Lynx_ - Release i386 (20100816.1)]/ luci$
deb-src http://archive.ubuntu.com/ubuntu lucid main #Added by software-properti$

# deb cdrom:[Ubuntu 10.04.1 LTS _Lucid Lynx_ - Release i386 (20100816.1)]/ luci$
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.

deb http://archive.ubuntu.com/ubuntu lucid main
deb-src http://archive.ubuntu.com/ubuntu lucid main'. universe #Added by softwa$

## Major bug fix updates produced after the final release of the
## distribution.

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://archive.ubuntu.com/ubuntu lucid universe

And this was the response when I had Update Manager chk for updates:

Failed to fetch http://security.ubuntu.com/ubuntu/dists/lucid-security/Release Unable to find expected entry main'./binary-i386/Packages in Meta-index file (malformed Release file?)
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/lucid/Release Unable to find expected entry main'./binary-i386/Packages in Meta-index file (malformed Release file?)
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/lucid-updates/Release Unable to find expected entry main'./binary-i386/Packages in Meta-index file (malformed Release file?)
Some index files failed to download, they have been ignored, or old ones used instead.

Please try to put this into your /etc/apt/sources.list

###### Ubuntu Main Repos
deb http://archive.ubuntu.com/ubuntu/ lucid main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ lucid main restricted universe multiverse

###### Ubuntu Update Repos
deb http://archive.ubuntu.com/ubuntu/ lucid-security main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ lucid-updates main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ lucid-proposed main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ lucid-backports main restricted universe multiverse

deb-src http://archive.ubuntu.com/ubuntu/ lucid-security main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ lucid-updates main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ lucid-proposed main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ lucid-backports main restricted universe multiverse

###### Ubuntu Partner Repo
deb http://archive.canonical.com/ubuntu lucid partner
deb-src http://archive.canonical.com/ubuntu lucid partner

Marco, I did using sudo gedit command from a Terminal window. Highlighted and pasted your script and got this when I hit "Check" in the Update Mgr.:

Failed to fetch http://ftp.usf.edu/pub/ubuntu/dists/lucid-updates/Release Unable to find expected entry main'./binary-i386/Packages in Meta-index file (malformed Release file?)
Failed to fetch http://security.ubuntu.com/ubuntu/dists/lucid-security/Release Unable to find expected entry main'./binary-i386/Packages in Meta-index file (malformed Release file?)
Failed to fetch http://ftp.usf.edu/pub/ubuntu/dists/lucid-security/Release Unable to find expected entry main'./source/Sources in Meta-index file (malformed Release file?)
Failed to fetch http://ftp.usf.edu/pub/ubuntu/dists/lucid/Release Unable to find expected entry main'./binary-i386/Packages in Meta-index file (malformed Release file?)
Some index files failed to download, they have been ignored, or old ones used instead.

Could I just be doing something wrong somehow?

Just wanted to add, if it makes any diff: According to the Update Mgr., my system is now 35 days out of date. So it's getting SOME info, right?

Please verify again the content of your /etc/apt/sources.list and retry...
be sure the file contain only the rows previously posted...

YEEHAW!!!! THANK YOU, THANK YOU, THANK YOU!!!! If you were here I'd kiss you and make you a HUGE breakfast of fresh laid eggs and some nice bacon w/ home fries on the side !!!!

Thanks actionparsnip, that solved my question.