Older blog entries for amits (starting at number 79)

10 Jan 2013 (updated 22 May 2013 at 11:16 UTC) »

About Random Numbers and Virtual Machines

Several applications need random numbers for correct and secure operation.  When ssh-server gets installed on a system, public and private key paris are generated.  Random numbers are needed for this operation.  Same with creating a GPG key pair.  Initial TCP sequence numbers are randomized.  Process PIDs are randomized.  Without such randomization, we’d get a predictable set of TCP sequence numbers or PIDs, making it easy for attackers to break into servers or desktops.


On a system without any special hardware, Linux seeds its entropy pool from sources like keyboard and mouse input, disk IO, network IO, and any other sources whose kernel modules indicate they are capable of adding to the kernel’s entropy pool (i.e .the interrupts they receive are from sufficiently non-deterministic sources).  For servers, keyboard and mouse inputs are rare (most don’t even have a keyboard / mouse connected).  This makes getting true random numbers difficult: applications requesting random numbers from /dev/random have to wait for indefinite periods to get the randomness they desire (like creating ssh keys, typically during firstboot.).


For applications that need random numbers instantaneously, but can make do with slightly low-quality random numbers, they have the option of getting their randomness from /dev/urandom, which doesn’t block to serve random numbers — it’s just not guaranteed that the numbers one receives from /dev/urandom truly reflect pure randomness.  Indiscriminate reading of /dev/urandom will reduce the system’s entropy levels, and will starve applications that need true random numbers.  Random numbers in a system are a rare resource, so applications should only fetch them when they are needed, and only read as many bytes as needed.


There are a few random number generator devices that can be plugged into computers.  These can be PCI or USB devices, and are fairly popular add-ons on servers.  The Linux kernel has a hwrng (hardware random number generator) abstraction layer to select an active hwrng device among several that might be present, and ask the device to give random data when the kernel’s entropy pool falls below the low watermark.  The rng-tools package comes with rngd, a daemon, that reads input from hwrngs and feeds them into the kernel’s entropy pool.


Virtual machines are similar to server setups: there is very little going on in a VM’s environment for the guest kernel to source random data.  A server that hosts several VMs may still have a lot of disk and network IO happening as a result of all the VMs it hosts, but a single VM may not be doing much to itself generate enough entropy for its applications.  One solution, therefore, to sourcing random numbers in VMs is to ask the host for a portion of the randomness it has collected, and feed them into the guest’s entropy pool.  A paravirtualized hardware random number generator exists for KVM VMs.  The device is called virtio-rng, and as the name suggests, the device sits on top of the virtio PV framework.  The Linux kernel gained support for virtio-rng devices in kernel 2.6.26 (released in 2008).  The QEMU-side device was added in the recent 1.3 release.


On the host side, the virtio-rng device (by default) reads from the host’s /dev/random and feeds that into the guest.  The source of this data can be modified, of course.  If the host lacks any hwrng, /dev/random is the best source to use.  If the host itself has a hwrng, using input from that device is recommended.


Newer Intel architectures (IvyBridge onwards) have an instruction, RDRAND, that provides random numbers.  This instruction can be directly exposed to guests.  Guests probe for the presence of this instruction (using CPUID) and use it if available.  This doesn’t need any modification to the guest.  However, there’s one drawback to exposing this instruction to guests: live migration.  If not all hosts in a server farm have the same CPU, live-migrating a guest from one host that exposes this instruction to another that doesn’t, will not work.  In this case, virtio-rng in the host can be configured to use RDRAND as its source, and the guest can continue to work as in the previous example.  This is still sub-optimal, as we’ll be passing random numbers to the guest (as in the case of /dev/random), instead of real entropy.  The RDSEED instruction, to be introduced later (Broadwell onwards) will provide entropy that can be safely passed on to a guest via virtio-rng as a source of true random entropy, eliminating the need to have a physical hardware random number generator device.


It looks like QEMU/KVM is the only hypervisor that has the support for exposing a hardware random number generator to guests.  (One could pass through a real hwrng to a guest, but that doesn’t scale and isn’t practical for all situations — e.g. live migration.)  Fedora 19 will have QEMU 1.4, which has the virtio-rng device, and even older guests running on top of F19 will be able to use the device.


For more information on virtio-rng, see the QEMU feature page, and the Fedora feature page.  LWN.net has an excellent article on random numbers, based on H. Peter Anvin’s talk at LinuxCon EU 2012.


Updated 2013 May 22: Added info about RDSEED and the Fedora feature page, corrected few typos.

Syndicated 2013-01-10 20:57:30 (Updated 2013-05-22 10:17:40) from Think. Debate. Innovate. - Amit Shah's blog

9 Jan 2013 (updated 22 May 2013 at 11:16 UTC) »

Workarounds for common F18 bugs

I’ve been using the Fedora 18 pre-release for a couple of months now, and am generally happy with how it works.  I filed quite a few bugs, some got resolved, some not.  Here’s a list of things that don’t work as they used to in the past, with workarounds so they may help others:

  • Bug 878619Laptop always suspends on lid close, regardless of g-s-t policy: I used to set the action on laptop lid close to lock the screen by default, instead of putting it in the suspend state.  I used to use the function keys or menu item to suspend earlier.  However, with GNOME 3.6 in F18, the ‘suspend’ menu item has gone away, replaced by ‘Power Off’.  The developers have now removed the dconf settings to tweak the action of lid close (via gnome-tweak-tool or dconf-editor).  As described in GNOME Bug 687277, this setting can be tweaked by adding a systemd inhibitor:
    systemd-inhibit --what=handle-lid-switch \
                    --who=me \
                    --why=because \
                    --mode=block /bin/sh
  • Bug 887218 – 0.5.0-1 regression: 147e:2016 Upek fingerprint reader no longer works: fprintd may not remember the older registered fingerprints, re-registering them is a workaround.
  • Bug 878412Cannot assign shortcuts to switch to workspaces 5+: I use keyboard shortcuts (Ctrl+F<n>) to switch workspaces.  Till F16, I could assign shortcuts to as many workspaces as are currently in use.  Curiously, with F18, shortcuts can only be assigned to workspaces 1 through 4.  This was a major productivity blocker for me, and an ugly workaround is to create a shell script that switches workspaces via window manager commands: install ‘wmctrl’, and create custom shortcuts to switch workspaces by invoking ‘wmctrl -s <workspace-1>’.  wmctrl counts workspaces from 0, so to switch to workspace 5, invoke ‘wmctrl -s 4′.
  • Bug 878736Desktop not shown after unlocking screensaver: This one is due to some focus-stealing apps and gnome-shell’s new screensaver not working together.  I use workrave, an app that helps me keep my eyesight and wrists in relatively good shape.  Other people have complained even SDL windows (games, qemu VMs, etc.) interact badly with the new screensaver.  For my workaround, I’ve set workrave to not capture focus for now.
  • Bug 878981“Alt + Mouse click in a window + mouse move” doesn’t move windows anymore: The modifier key is now changed to the ‘Super’ key, so Super + mouse click + mouse move works in a similar way to how using the Alt key worked earlier.  I’m still lacking the window resize modifier that KDE offers (modifier key + right-click+mouse move)
  • Bug 878428__git_ps1 not found: I’ve discussed this earlier.

Other than these, a couple of bugs that affect running F18 in virtual machines:

  • Bug 864567display garbled in KVM VMs on opening windows: Using any other display driver for the guest other than cirrus works fine.
  • Bug 810040 – F17/F18 xen/kvm/vmware/hyperv guest with no USB: gnome-shell fails to start if fprintd is present: I mentioned this earlier as well: remove fprintd in the VM, or add ‘-usb’ to the qemu command line.

Syndicated 2013-01-09 13:24:36 (Updated 2013-05-22 10:24:38) from Think. Debate. Innovate. - Amit Shah's blog

7 Dec 2012 (updated 22 May 2013 at 11:16 UTC) »

Mystery Shopper Needed

Most of the spam I receive gets caught by spam filters, and pushed into the separate spam folder.  I check the folder once in a while for false positives.

A recent message in my spam folder, with the subject ‘Mystery shopper needed’ caught my attention:

Mystery Shopper needed

We have post of Mystery Shopper in your area. All you need is to act like a customer, you be will surveying different outlets like Walmart, Western Union, etc and provide us with detailed information about their service.

You will get $200.00 per one task and you can handle as many tasks as you want. Each assignment will take one hour and it wont affect your present occupation because it is flexible.

Before any task we will give you with the resources needed. You will be sent a check or money order, which you will cash and use for the task. Included to the  check would be your assignment payment, then we will provide you details through email. You just need to follow instruction given to you as a Secret Shopper.

If you are interested, please fill in the details below and send it back to us to john_paul2_john@aol.com for approval.

First Name:
Last Name:
Full Address:
City, State and Zip code:
Cell and Home Phone Numbers:

Hope to hear from you soon.

Head of Operations,
John Paul.

I can’t resist going shopping — and being paid for it!  Posted this here in case anyone else missed this email due to “bad” spam filters.  We don’t have Walmart here yet, but we certainly do have Western Union.

PS: If you’re interested in treasure hunts: can you spot who’s actually sending these messages?

Return-Path: <john@rapanuiviaggi.redacted>
Delivered-To: <redacted>
Received: (qmail invoked by alias); 28 Nov 2012 04:07:23 -0000
Received: from dns.hsps.ntpc.edu.tw (EHLO dns.hsps.ntpc.edu.tw) []
        by mx0.gmx.net (mx002) with SMTP; 28 Nov 2012 05:07:23 +0100
Received: from dns.hsps.ntpc.edu.tw (localhost [])
        by dns.hsps.ntpc.edu.tw (Postfix) with ESMTP id C5BD97DF740D;
           Wed, 28 Nov 2012 10:34:02 +0800 (CST)
Received: from dns.hsps.ntpc.edu.tw (localhost [])
        by dns.hsps.ntpc.edu.tw (Postfix) with ESMTP id 7DA667DF7379;
           Wed, 28 Nov 2012 10:34:02 +0800 (CST)
From: "John Paul." <john@rapanuiviaggi.redacted>
Reply-To: john_paul2_john@aol.com
Subject: Mystery Shopper needed.
Date: Wed, 28 Nov 2012 10:34:02 +0800
Message-Id: <20121128023012.M26524@rapanuiviaggi.redacted>
X-Mailer: OpenWebMail 2.52 20060502
X-OriginatingIP: (web2)
MIME-Version: 1.0
Content-Type: text/plain;
To: undisclosed-recipients: ;
X-NetStation-Status: PASS
X-NetStation-SPAM: 0.00/5.00-8.00

Syndicated 2012-12-07 06:37:41 (Updated 2013-05-22 10:28:15) from Think. Debate. Innovate. - Amit Shah's blog

20 Nov 2012 (updated 22 May 2013 at 11:16 UTC) »

__git_ps1 not found after upgrade to Fedora 18

If you have enabled git information in the shell prompt (like branch name, working tree status, etc.) [1], an upgrade to F18 breaks this functionality.  What’s worse, __git_ps1 (a shell function) isn’t found, and a yum plugin goes looking for a matching package name to install, making running any command on the shell *very* slow.

A workaround, till the bug is fixed, is to do:

ln -s /usr/share/git-core/contrib/completion/git-prompt.sh  /etc/profile.d/

Bug 878428, if you want to track progress.

[1] To add such git information in the shell display (for bash), add this to your .bashrc file:

export PS1='\[\033[00;36m\]\u@\h\[\033[00m\]:\[\033[01;34m\] \w\[\033[00m\]$(__git_ps1 " (%s)")\$ '

Syndicated 2012-11-20 12:22:00 (Updated 2013-05-22 10:26:58) from Think. Debate. Innovate. - Amit Shah's blog

18 Nov 2012 (updated 22 May 2013 at 11:16 UTC) »

Avi Kivity Stepping Down from the KVM Project

Avi Kivity giving his keynote speech

Avi Kivity announced he is stepping down as (co-)maintainer of the KVM Project at the recently-concluded KVM Forum 2012 in Barcelona, Spain.  Avi wrote the initial implementation of the KVM code back at Qumranet, and has been maintaining the KVM-related kernel and qemu code for about 7 years now.

In his keynote speech, he mentioned he’s founding a startup with a friend, and hopes to create new technology as exciting as KVM.  He also mentioned they’re in stealth mode right now, so questions about the new venture didn’t get any answers.

He returned to the stage on the second day of the Forum to talk about the new memory API work he’s been doing in qemu, and in his typical dry humour, he mentioned he was supposed to vanish in a puff of smoke after his keynote, but the special effects machinery didn’t work, so he was back on stage.  Avi later rued the lack of laughter at this joke, and that made him very sad.  To offer him some consolation, it was pointed out that not everyone knew of his departure, as many had missed his keynote.  He quipped “that’s even worse than not getting laughs”.

His leadership, as well as his humour, will be missed.  Personally, he’s helped me grow during the last few years we’ve worked together.  But I’m sure whatever he’s working on will be something to look forward to, and we’re not really bidding him adieu from the tech world.

Syndicated 2012-11-18 06:32:05 (Updated 2013-05-22 10:31:17) from Think. Debate. Innovate. - Amit Shah's blog

28 Oct 2012 (updated 22 May 2013 at 11:16 UTC) »

Setting Up Your Free Private Feed Reader

I’ve tried several RSS feed readers, offline as well as online: aKregator, Liferea, rss2email being the ones tried for a long time. One drawback with these offline tools is they may miss feeds when I’m offline for prolonged periods (travel, vacations, etc.). Also, they’re tied to one device; can’t switch laptops and have the feeds be in sync. I tried Google Reader for a while as well, for a solution in the “cloud”, which worked for a while, but not anymore.

So I started to search for an online feed reader, preferably with hosting services, since I didn’t want to keep up with updates to the software. I found several free readers, and Tiny Tiny RSS seemed like a really good option.  The developer hosts an online version of the reader, which I used for quite a while.  (The online service is soon going to be discontinued.)  I was quite content with that option, but when OpenShift was launched, I thought I’d try hosting tt-rss myself: it initially began as an experiment to using OpenShift. Then, when I moved this blog to OpenShift, I realised it didn’t really take much effort to host the blog, and that I could switch my primary instance of tt-rss from the developer-hosted instance to my own. It turned out to be really easy, and here I’ll share my recipe.

I first grabbed the ttrss sources from the git repo:

cd ~/src/
git clone git://github.com/gothfox/Tiny-Tiny-RSS.git

I then created an OpenShift php app.

cd ~/openshift
rhc app create -a ttr -t php-5.3

Then, added a mysql db and the phpmyadmin tool to manage the db, in case something goes wrong sometime.

rhc-ctl-app -e add-mysql-5.1 -a ttr
rhc-ctl-app -e add-phpmyadmin-3.4 -a ttr

After this initial setup, I copied all the files from the ttrss src dir to the php/ directory of the OpenShift repo:

cp -r ~/src/Tiny-Tiny-RSS/* ~/openshift/ttr/php/

Next is to add all the files to the git repo:

cd ~/openshift/ttr/
git add php
git commit -m 'Add tt-rss sources'

Now to set up the environment on the server for tt-rss to work in. E.g. creating directories where tt-rss will store its feed icons, temporary files, etc. This is needed, as the OpenShift git directory is transient: it’s deleted and re-created whenever ‘git push’ is done. So to store persistent data between git pushes, we need to use the OpenShift data directory. Create an app build-time action hook to setup the proper directory structure each time the app is built (i.e. after a git push). Learn more about the different build hooks here.

Edit the .openshift/action_hooks/build file, so it looks like this:

# This is a simple build script, place your post-deploy but pre-start commands
# in this script.  This script gets executed directly, so it could be python,
# php, ruby, etc.


if [ ! -d $TMP_DIR ]; then
    mkdir $TMP_DIR

if [ ! -d $LOCK_DIR ]; then
    mkdir $LOCK_DIR

if [ ! -d $CACHE_DIR ]; then
    mkdir $CACHE_DIR

if [ ! -d $CACHE_DIR/export ]; then
    mkdir $CACHE_DIR/export

if [ ! -d $CACHE_DIR/images ]; then
    mkdir $CACHE_DIR/images

Make this file executable, and commit the result:

chmod +x .openshift/action_hooks/build
git add .openshift/action_hooks/build
git commit -m 'build hook: create and link to persistent RW directories'

Next was to create the tt-rss config file from the provided template:

cd ~/openshift/ttr/php/
cp config.php-dist config.php

And then editing the config file.

First, the DB info. I created a new db user via the phpmyadmin interface, but you can use the default admin user as well.

        define('DB_TYPE', "mysql");
        define('DB_HOST', $_ENV['OPENSHIFT_DB_HOST']);
        define('DB_USER', "<user>");
        define('DB_NAME', "ttr");
        define('DB_PASS', "<your pass>");
        //define('DB_PORT', '5432'); // when neeeded, PG-only

Next come the files and directories section:

        define('LOCK_DIRECTORY', $_ENV['OPENSHIFT_DATA_DIR'] . "/lock");
        // Directory for lockfiles, must be writable to the user you run
        // daemon process or cronjobs under.

        define('CACHE_DIR', $_ENV['OPENSHIFT_DATA_DIR'] . '/cache');
        // Local cache directory for RSS feed content.

        define('TMP_DIRECTORY', $_ENV['OPENSHIFT_DATA_DIR'] . "/tmp");
        // Directory for temporary files

        define('ICONS_DIR',  $_ENV['OPENSHIFT_DATA_DIR'] . '/icons');
        define('ICONS_URL', "ico");

The last icons bit is a modification from the default of ‘feed-icons’. If you’re setting up a new repo, there’s no need to deviate from the default, but when I had deployed the tt-rss instance, the default icons directory was ‘icons’, which unfortunatley clashes with Apache’s idea of what $URL/icons is. So I used ‘ico’. Remember to modify the bit in the build hook above to create the appropriate symlink if this ICONS_URL is changed.

These config settings are the ones specific to OpenShift. Modify the others to suit your needs.

Lastly, add a cron job to update the feeds at an hourly interval:

cd ~/openshift/ttr
mkdir .openshift/cron/hourly

I created a new file, called update-feeds.sh, in the new .openshift/cron/hourly directory, and added the following to it:


$OPENSHIFT_REPO_DIR/php/update.php -feeds >/dev/null 2>&1
date >> $OPENSHIFT_LOG_DIR/update-feeds.log

For troubleshooting cron jobs, you can append custom output to any file in the log directory, like the date being output above. For other ways to update feeds, refer to the tt-rss documentation.

Add this file to git:

cd ~/openshift/ttr
git add .openshift/cron/hourly/update-feeds.sh
git commit -m 'add hourly cron job to update feeds'

Lastly, push the result to the OpenShift servers:

git push

That’s it! Enjoy your completely free (free as in freedom, as well as free as in beer) and personal feed reader in the clouds.

Syndicated 2012-10-28 16:36:14 (Updated 2013-05-22 10:29:35) from Think. Debate. Innovate. - Amit Shah's blog

14 Sep 2012 (updated 22 May 2013 at 11:16 UTC) »

Virtualization at the Linux Plumbers Conference 2012

The 2012 edition of the Linux Plumbers Conference concluded recently.  I was there, running the virtualization microconference.  The format of LPC sessions is to have discussions around current as well as future projects.  The key words are ‘discussion’ (not talks — slides are optional!) and ‘current’ and ‘future’ projects — not discussing work that’s already done; rather discussing unsolved problems or new ideas.  LPC is a great platform for getting people involved in various subsystems across the entire OS stack in one place, so any sticky problems tend to get resolved by discussing issues face-to-face.

The virt microconf had A LOT of submissions: 17 topics to be discussed in a standard time slot of 2.5 hours for one microconf track.  I asked for a ‘double track’, making it 5 hours of time for 17 topics.  Still difficult, but reducing a few topics to ‘lightning talks’, we could get a somewhat decent 20 minutes per topic.  I contemplated between rejecting topics and thus increasing the time each discusison would get, or keeping all the topics, and asking the people to wrap up in 20 minutes.  I went for the latter — getting more stuff discussed (and hence, more problems / issues ‘out there’) is a better use of time, IMO.  That would also ensure that people stay on-topic and focussed.

There was also a general change in the way microconfs were scheduled this time: the microconfs were not given a complete 2.5-hour slot.  Rather, they were given 3 slots of 45 minutes each.  This helped the schedule pages to show the topics of the microconfs being discussed at that time, so the attendees could pick and choose the discussion they wanted to attend, rather than seeing a generic ‘Virtualization Micrconf’ slot.  I think this was a good idea.  Individual microconf owners could request for modifications to this scheme, of course, and some microconfs just chose to run the entire session in one slot, or reserved one whole day in a room, etc.  For the virt microconf, I went with six separate slots, scheduled in a way to avoid conflicts with other virt-related topics in other sessions, giving a total of 4.5 hours for 17 topics.

I segregated the CFP submissions so I could schedule related discussions in one slot, to avoid jumping between subjects and to also help concentrate on specifics in an area.  Two submissions, one on security and one on storage, were by themselves, so I clubbed them into one ‘security and storage‘ session.  The others were nicely aligned, so we could have ‘x86‘, ‘MM‘, ‘ARM‘, ‘Networking‘ and ‘lightning talks’ topics in separate slots.  Since there were 4 network-related talks, I asked for a double slot (two 45-min slots back-to-back), and clubbed the lightning talks in the same session, which was scheduled to be the last session for the virt microconf.

Given this, I would say the microconf went quite well — the notes and slides are up at the LPC 2012 virt microconf wiki, and we could get good discussions going for most of the topics, given the time constraints.  Of course, a major benefit of going to conferences is to meet people outside of the sessions, in the hallways and at social events, and the discussions continued there as well.  I did bank on this extra time we would have into the ‘reject vs take all of them’ problem mentioned earlier.  From what I heard, the beer at the social events failed to stop technical discussions, so it all worked out for the best.

Each microconf owner (or a representative) had to do a short summary at the end of the LPC, for the benefit of the people not present for some sessions.  I did the virt summary in roughly these words:

We had a quite productive virtualization microconfierence.  We received a lot of submissions, and accepted them all, which meant we had to limit the time for each discussion in the slots, but we could divide the slots by a general topic, effectively increasing the discussion time for the larger topic.


We had a healthy representation from the KVM as well as Xen sides.  For example, in the MM topic, we discussed NUMA awareness for KVM as well as Xen.  Dario Faggioli presented the Xen side, and Andrea Arcangeli spoke on the Linux/KVM side.  Andrea spoke about AutoNUMA. It has been contentious on the mailing lists, and from the Kernel Summit discussions, it looked like some agreement will be reached soon.  Xen uses a similar approach to AutoNUMA, and they would end up pushing the patches soon as well.  Daniel Kiper spoke about integrating the various balloon drivers in the kernel to remove code duplication.


Both AMD and Intel publically announced new hardware features for interrupt virtualization for the first time here, and it was interesting to see them compare notes and find out what the other is doing and how, for example do they support IOMMU?  x2apic?  Etc.


New ARM architecture support work was presented by Marc Zyngier for the KVM effort, and Stefano Stabellini for the Xen effort.  Much of the work seems to be done, and patches are in a shape to be applied for the next merge window.  There are a few open issues, and they were discussed as well.


We had quite a few talks for the networking session.  Alex Williamson spoke about VFIO, which seemed to get mentioned a lot throughout the conference in multiple sessions.  This is a new way of doing device assignment, and progress looks positive, with the kernel side already merged in 3.6, and qemu patches queued up for 1.3.  Alex Graf then talked about ‘semi-assignment’, a way to do device assignment (or pci passthrough) while also getting proper migration support.  The effort involved writing device emulation for each device supported, and the approach wasn’t too popular.  IBM and Intel guys have been doing virtio net scalability testing, and John Fastabend spoke about some optimisations, which were generally well-received.  We should expect patches and more benchmarks soon.  Vivek Kashyap spoke about network overlays, and how creating a tunnel for networks for VMs can help with VM migration across networks.


We also had a session on security, by Paul Moore, who gave an overview of the various methods to secure VMs, specifically the new seccomp work.


Lastly, we had Bharata Rao talk about introducing a glusterfs backend for qemu, replacing qemu’s block drivers, which gives more flexibility in handling disk storage for VMs.


The organisers are collecting feedback, so if you were there, be sure to let them know of your experience, and what we could do better in the coming years.

I’d like to thank the Linux Foundation and the Linux Plumbers Conf organisers for giving me the opportunity to be there and run the virt microconf.

Syndicated 2012-09-14 05:07:30 (Updated 2013-05-22 10:32:25) from Think. Debate. Innovate. - Amit Shah's blog

27 Jun 2012 (updated 22 May 2013 at 11:16 UTC) »

Changing GNOME Default Action for Low Battery

The GNOME default of ‘hibernate’ or suspend-to-disk on very low battery power isn’t optimal for many laptops — hibernate is known to be broken on several hardware setups, it frequently results in file system corruption, and just causes pain.  That, combined with the weird behaviour of the GNOME power manager to put the system in hibernate, even when the battery isn’t low, annoyed me enough to go hunting for a way to change the default.

The GUI doesn’t expose a ‘sleep’ setting; it just offers hibernate and shutdown, so here’s a tip to just put the system to sleep state (suspend to RAM), which is a much well-behaved default for me.

Install dconf-editor, and go to


and modify the


to suspend.

For the curious, the weird behaviour of the GNOME power manager I mentioned above is noted in these bug reports:

Bug 673220 – ‘Critical capacity’ warning on laptop with multiple batteries broken
Bug 673221 – Shutdown action on battery low doesn’t save session
Bug 673222 – More prominent warning, at least 5-10% before battery goes critically low
Bug 673223 – System enters shutdown/hibernate even when power connected but battery low

Syndicated 2012-06-27 05:47:53 (Updated 2013-05-22 10:33:28) from Think. Debate. Innovate. - Amit Shah's blog

Workaround for error after upgrading VM from F16 to F17

Updating a Fedora 16 guest to a Fedora 17 guest via preupgrade gave me the ‘Oh no, something has gone wrong!’ screen at the GDM login screen.  It’s quite frustrating to see that screen because you can’t switch to a virtual terminal for troubleshooting, or even reboot or shutdown.

To send the key sequence Ctrl+Alt+F2 to the guest to switch to a virtual terminal, use the qemu monitor by pressing


and use sendkey to send the key sequence:

(qemu) sendkey ctrl-alt-f2

Then go back to the guest window by issuing


After logging in as root, I poked in the gdm log files in /var/log/gdm/ and saw the fprint daemon was causing some errors.  Removing the fprintd package fixed this, but this is just a workaround, not a solution:

yum remove fprintd

Bug filed.

Syndicated 2012-06-04 11:47:10 (Updated 2012-06-04 11:48:12) from Think. Debate. Innovate. - Amit Shah's blog

11 May 2012 (updated 12 May 2012 at 14:10 UTC) »

Using adb To Copy Files To / From Your Android Device

Some devices, like the Galaxy Nexus and the HP Touchpad* (via the custom Android ROMs) don’t expose themselves as USB storage devices.  They instead use MTP or PTP to transfer media files (limiting to only photos and audio/video files being shown from the device).

This happens due to there being no separate sdcard on these devices, and ‘unplugging’ an sdcard from a running device to be exposed to the connected computer could cause running apps on the device itself to malfunction.  Android developer Dan Morill explains this here. He also mentions how the Nexus S doesn’t have this problem.

There are several apps that can open shares to the device using one of several protocols (DAV, SMB, etc.).  However, one quick way I’ve found to copy files to and from the device connected via USB to a computer is by using the adb tool.  It’s available as part of the ‘android-tools’ package on Fedora.

To copy a file from the computer to an android device connected via usb, use this:

adb push /path/to/local/file /mnt/sdcard/path/to/file

This will copy the local file to the device in the specified location.  Directories can be created on the device via the shell:

adb shell

and using the usual shell commands to navigate around and create directories.

* On the Touchpad, WebOS can expose the storage as a USB Storage Media.  The current nightly builds of CM9 can’t.

Syndicated 2012-05-11 11:10:16 (Updated 2012-05-12 14:07:59) from Think. Debate. Innovate. - Amit Shah's blog

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