create Infrequently Asked Questions

docs/misc/iaq.md

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+Infrequently Asked Questions
+============================
+
+### For troubleshooting, how can I disable Xen Meltdown mitigations?
+
+Set `xpti=false` option in Xen command line (xen.gz option in grub, or options= line in xen.cfg for UEFI).
+
+### What is a good IDE for Qubes?
+
+QtCreator
+
+### What is the process flow when starting an AppVM under Qubes R4.x?
+
+1. qvm-start sends a request to qubesd, using Admin API
+2. qubesd starts required netvm (recursively), if needed
+3. qubesd request qmemman to allocate needed memory for new VM (according to VM's 'memory' property)
+4. qubesd calls into appropriate storage pool driver to prepare for VM startup (create copy-on-write layers etc)
+5. qubesd gathers needed VM properties etc and builds libvirt VM configuration (XML format, can be seen using `virsh dumpxml`)
+6. qubesd calls into libvirt to start the VM (but in paused mode)
+7. libvirt setup the VM using libxl, this include starting stubdomain if needed
+8. qubesd start auxiliary processes, including:
+   - qrexec-daemon
+   - qubesdb-daemon (and fill its content)
+9. libvirt unpause the VM
+10. qvm-start-gui process (running separately from qubesd, as part of dom0 user GUI session) starts gui daemon
+
+See "source" link [here](https://dev.qubes-os.org/projects/core-admin/en/latest/qubes-vm/qubesvm.html#qubes.vm.qubesvm.QubesVM.start).
+
+### For troubleshooting, how can I switch R4.0 stubdomains back to qemu-traditional?
+
+~~~
+qvm-features VMNAME linux-stubdom ''
+~~~
+
+### How can I contribute to developing Qubes Windows Tools for R4.0?
+
+See [this post](https://www.mail-archive.com/qubes-devel@googlegroups.com/msg02808.html) and thread.
+
+### Where are VM log files kept?
+
+In the `/var/log/libvirst/libxl/`, `/var/log/qubes/` and `/var/log/xen/console/` directories.
+
+### How can I upgrade everything to testing?
+
+dom0: `sudo qubes-dom0-update --enablerepo=qubes-dom0-current-testing --clean` (or --check-only instead for dom0).
+
+fedora: `sudo dnf update --enablerepo=qubes-vm-*-current-testing --refresh`
+
+debian/whonix: `sudo apt-get update -t *-testing && sudo apt-get dist-upgrade -t *-testing`
+
+This way, you don't need to edit any files for debian/whonix to get the testing.
+If you also want to increase reliability further, you can make a dependency/cache check with "sudo apt-get check", which is normally very quick.
+For that, under debian/whonix do: `sudo apt-get check && sudo apt-get update -t *-testing && sudo apt-get dist-upgrade -t *-testing`.
+
+### How can I set environment variables for a VM?
+
+Either add to `/etc/environment` or create `~/.envsrc` and set a variable there, then create `.xsessionrc` and source `~/.envsrc`.
+See [this thread](https://www.mail-archive.com/qubes-users@googlegroups.com/msg20360.html).
+
+### How would I enable sudo authentication in a Template?
+
+There are two ways to do this now:
+
+1. Follow this [Qubes doc](https://www.qubes-os.org/doc/vm-sudo/#replacing-password-less-root-access-with-dom0-user-prompt) to get the yes/no auth prompts for sudo.
+
+2. Remove the 'qubes-core-agent-passwordless-root' package.
+
+This second way means that sudo no longer works for a normal user. 
+Instead, any root access in the VM must be done from dom0 with a command like `qvm-run -u root vmname command`.
+
+### VM fail to start after hard power off
+
+I realized that some VMs refuse to start after a hard power-off (hold power button for 10s).
+When running `qvm-start test` I get `vm-test-private missing`.
+But this thin volume is actually there.
+Also the volume `vm-test-private-snap` is still present.
+
+Try this in dom0:
+~~~
+sudo pvscan --cache --activate ay
+sudo systemctl restart qubesd
+qvm-start test
+~~~
+
+### How can I provision a VM with a larger/non-standard swap and /tmp?
+
+Fedora's /tmp uses tmpfs ; it's mounted by systemd at boot time.
+See `systemctl status tmp.mount` and `/usr/lib/systemd/system/tmp.mount.d/30_qubes.conf` to increase its size.
+Alternatively you can increase the size afterwards with `mount -o remount,size=5G /tmp/`.
+
+If you need to have a disk based tmp you'll have to mask the systemd unit (`systemctl mask tmp.mount`) and put a fstab entry for /tmp.
+
+Alternatively you can add swap with a file inside the vm but it's a bit ugly:
+~~~
+dd if=/dev/zero of=swapfile bs=1M count=1000
+mkswap swapfile
+swapon swapfile
+~~~
+
+
+
+*Thanks to all mailing list contributors, from where most of these came.*