First of all, this issue seems to have resolved itself for some reason that I dont know of. I'd still like to know what it was and why it appeared. If not for me, then for someone else.

I installed debian on a new machine (sort of new, anyways) and when everything was working I edited the /etc/apt/sources.list as I usually do, adding 'testing' package lists.
I run the apt-get update.
After the update has gone through, I get the following error:
E: Dynamic MMap out of room!

After this, I figured there was something wrong with the testing mirrors and I put in stable instead, just to give it a try, and voila! It went through without a hitch. However, on my other boxes, the testing mirrors worked fine, so I went back to the new box but still the same error with the testing mirrors. Today however, it seems to be working.

Someone told me to add " APT::Cache-Limits 10000000; " to /etc/apt/apt.conf, which I did but it didnt matter at all. I dont even have an /etc/apt/apt.conf in either of my boxes, but I created it anyways.

Now the system is running with the testing packages as I want, and all seems to be working. However, I'm still curious on what this error was.

/d

the content of /etc/apt/apt.conf should be:

That'll do it. Your post had "Cache-Limits. Perhaps the syntax is enough to fix it (if it breaks again).

That worked for me, except I had to use a higher number. Values of 12000000 and even 20000000 worked, so the advice I would add is to keep trying higher values until it works. The man page for apt.conf doesn't say what the maximum value for this parameter can be, so I don't know if there is a maximum value for it.

Also, on my system the file to modify was not /etc/apt/apt.conf, but /etc/apt/apt.conf.d/70debconf.

Don't know exactly what is the default size but apt has a package cache size limit adding more repositories will take you over it and give you the error, telling it to use a higher size for the cache eliminates the problem. I use APT::Cache-Limit 20000000; in the file it seems to work fine with it.

using APT::Cache-Limit "20000000"; worked for me

My error seems to have been the exact same one:

so if I get it right, this is the maximum data apt will cache, right? A simple apt-get clean, or even better, apt-get autoclean would have clear your cache then, no?

Hi. I'm new here and had same problem.
and I fixed .
I giving credit for this jake. http://www.yak.net/fqa/416.html
In my case I had to do this in /etc/apt/apt.conf.d/70debconf.

During apt-get update, you may see this error.
The simple way to solve it is like so:
cat << EOF >> /etc/apt/apt.conf.d/70debconf
APT::Cache-Limit "10000000";(hit return here)
EOF (hit return again).

I set APT::Cache-Limit "20000000"; just in case.

good luck.