History of some_hints_from_john

Q: I want to (re)mount a partition in a running guest ... but the guest has no rights (capability) to (re)mount?

A: I'll explain. I take as example your /tmp partition within the guest is too small, what will be likely the case if you stay with the 16MB default (vserver build mounts /tmp as 16 MB tempfs!).

<code>

# vnamespace -e XID mount -t tmpfs -o remount,size=256m,mode=1777 none /var/lib/vservers/<guest>/tmp/

</code>

Be warned that the guest will not recognize the change, as the /etc/mtab file is not updated when you mount like this. To permanently change the mount, edit /etc/vserver/<guest>/fstab on the host.

Q: How do I limit a guests RAM? I want to prevent OOM situations on the host!

A: First you can read [1].

If you want a recipe, do that:

1. Check the size of memory pages. On x86 and x86_64 is usually 4 KB per page.

2. Create /etc/vserver/<guest>/rlimits/

3. Check your physical memory size on the host, e.g. with "free -m". maxram = kilobytes/pagesize.

4. Limit the guests physical RAM to value smaller then maxram:

<code>

echo insertYourPagesHereSmallerThanMaxram > /etc/vserver/<guest>/rlimits/rss

</code>

5. Check your swapspace, e.g. with 'swapon -s'. maxswap = swapkilobytes/pagesize.

6. Limit the guest's maximum number of as pages to a value smaller than (maxram+maxswap):

<code>

echo desiredvalue > /etc/vserver/<guest>/rlimits/as

</code>

It should be clear this can still lead to OOM situations. Example: You have two guests and your as limit per guest is greater than 50% of (maxram+maxswap). If both guests request their maximum at the same point in time, there will be not enough mem .....

Q: Were can I get newer versions of VServer as ready made packages for Debian?

A: Here you go: http://linux-vserver.derjohn.de/ . There is also some stuff on backports.org, but my kernels are always 'devel' branch.