Archive for the 'Linux (general)' Category

Sync your Android contacts and calendars with your own server

It’s 2012, and there are still people who don’t put all their information onto Google/Facebook/… servers. Call them paranoid control freaks, if you want. 😉

Some of them even run their own e-mail server. Those people would probably prefer to have their address book(s) and calendar(s) stored on their own server as well, which Android cannot do out of the box.

This blog post aims to give a brief overview over my current solution to this problem. It’s not 100% perfect yet, but I am quite satisfied with it already. I have been using this setup for a couple of months now, and did not encounter any problems of relevance. (*)

Software components involved

On the server:

  • DAViCal – a free (GPL licensed) CalDAV/CardDAV server written in PHP; needs PostgreSQL as database server
  • Roundcube Webmail with the CardDAV plugin – to manage your contacts from within any web browser (Roundcube is of course also a decent mail client)

On the desktop / laptop computer:

  • Mozilla Thunderbird with
    • Lightning extension – to manage your calendar(s) from your Linux/Windows/Mac computer
    • SOGo connector extension (this link brings you to a file listing where you can download a nightly snapshot, there is no officially released version for current Thunderbird versions on the SOGo download page, yet) – to manage / lookup your contacts from your Linux/Windows/Mac computer

      A few words on how to get the SOGo connector working (it’s not really straight-forward, in my opinion): After installing the extension by dragging the downloaded .xpi file onto Thunderbird, open the Address book and choose Menu File / New / Remote Address Book. Enter the URL of your DAViCal CardDAV collection, i.e. https://your.server/davical/caldav.php/YOUR_USER/YOUR_COLLECTION. Then right-click on the new address book and choose Synchronize.

On the Android device:

  • CalDAV-Sync app from Market or AndroidPIT for a bit more than 2€

    (Since CalDAV-Sync is just a backend app that facilitates syncing, this is a screenshot of the Android calendar, with the event that can be seen in the Thunderbird-Lightning screenshot above)
  • CardDAV-Sync app from Market or AndroidPIT for a bit less than 1.50€ or free

    (Since CardDAV-Sync is just a backend app that facilitates syncing, this is a screenshot of the Android contact viewer, with the contact that can be seen in the Roundcube CardDAV screenshot above)
  • Contact Editor or Contact Editor Pro app from Market or AndroidPIT (Pro costs a bit more than 2€, the free version lacks a few features)

A few notes regarding the components:

  • Contact Editor is necessary because the default Android contact editor somehow does not work with custom contact sources. It integrates seamlessly once you have set it as default action upon adding/editing a contact for the first time after installation.
  • The SOGo connector extension for Thunderbird is a good start, but in the long run I really hope Thunderbird’s contact handling can be brought to a level that matches the rest of the application. There is hope.
  • There seems to be a calendar plugin for Roundcube as well (as part of the MyRoundcube plugin collection), and it seems to support CalDAV, but I couldn’t get it to work so far (and did not try hard, since I always have a Thunderbird with Lightning around, which is great for calendaring).

I’m planning to write more on how to get everything set up, but I currently don’t have time for that. The hardest part is getting DAViCal and PostgreSQL to work, in my opinion, all the other components basically just need a URL (to the previously set up DAViCal collection – e.g. https://your.server/davical/caldav.php/YOUR_USER/YOUR_COLLECTION), username and password to work.

Update (2012-01-28): Added some screenshots.
By the way, what must be a very recent change in Gentoo’s packaging of PHP causes CalDAV-Sync to fail syncing, and the apache error log contains “[Sat Jan 28 08:30:48 2012] [error] [client x.x.x.x] PHP Fatal error: Call to undefined function cal_days_in_month() in /…/davical/inc/RRule-v2.php on line 906” if you do not enable the ‘calendar’ USE flag for dev-lang/php (which is disabled by default).
Update (2012-01-29): (*) Typical, I write about something, and then it breaks. It seems there is an incompatibility between the newly released DAViCal 1.0.2 and CalDAV-Sync. The CalDAV-Sync developer has confirmed the issue and is working on it.
Update (2012-01-30): The incompatibility – resulting in logged error messages – does not affect functionality (it was just me having set the account to “One-Way-Sync”)
Update (2012-02-09): Great news: There are nightly builds of the SOGo connector Thunderbird extension that provides CardDAV integration for Thunderbird 10 now – I knew that extension before, but development seemed to have stopped at Thunderbird 3.5 or so. I added links and a bit of info above.
Update (2012-02-09/2): I found the first bug with SOGo connector – when saving a contact that has an image, the image gets lost. This doesn’t really matter to me, because I don’t use images in contacts usually, but for people who use images, this could be annoying. Hope they fix it.

Impact of ext4’s discard option on my SSD

Solid-state drives (SSDs) are seen as the future of mass storage by many. They are famous for their high performance: extremely low seek times, since there is no head that needs move to a position and then wait for the spinning disk to come around to where it needs to read/write; but also higher throughput of sequential data: My 2,5″ OCZ Vertex LE (100 GB) is rated at 235 MB/s sustained write speed, and read speeds up to 270 MB/s, for example.

There is a caveat though – quoting Wikipedia:

In SSDs, a write operation can be done on the page-level, but due to hardware limitations, erase commands always affect entire blocks. As a result, writing data to SSD media is very fast as long as empty pages can be used, but slows down considerably once previously written pages need to be overwritten. Since an erase of the cells in the page is needed before it can be written again, but only entire blocks can be erased, an overwrite will initiate a read-erase-modify-write cycle: the contents of the entire block have to be stored in cache before it is effectively erased on the flash medium, then the overwritten page is modified in the cache so the cached block is up to date, and only then is the entire block (with updated page) written to the flash medium. This phenomenon is known as write amplification.

So, SSDs are fast at writing, but only when their free space is neatly trimmed. The only component in your software stack that knows which parts of your SSD should be trimmed, is your file system. That is why there is a file system option in ext4 (my current file system of choice), called “discard”. When this option is active, space that is freed up in the file system is reported to the SSD immediately, and then the SSD does the trimming right away. This will make the next write to that part of the SSD as fast as expected. Obviously, trimming takes time – but how much time exactly? I wanted to find out, and did the following: I measured the time to unpack and then delete the kernel sources (36706 files amounting to 493 MB, which is what I call a big bunch of small files). I did it three times with and three times without the “discard” option, and then took the average of those three tries:

Without “discard” option:

  • Unpack: 1.21s
  • Sync: 1.66s (= 172 MB/s)
  • Delete: 0.47s
  • Sync: 0.17s

With “discard” option:

  • Unpack: 1.18s
  • Sync: 1.62s (= 176 MB/s)
  • Delete: 0.48s
  • Sync: 40.41s

So, with “discard” on, deleting a big bunch of small files is 64 times slower on my SSD. For those ~40 seconds any I/O is really slow, so that’s pretty much the time when you get a fresh cup of coffee, or waste time watching the mass storage activity LED.

Don’t enable the “discard” option if you have a similar SSD. A much better way to keep your free space neatly trimmed for good write speeds is, to trigger a complete walk over the file system’s free space, and tell the SSD to trim that all at once. And of course you would do that at times when you don’t actually want to use the system (e.g. in a nightly cron job, or with a script that gets launched during system shutdown). This can be done with the ‘fstrim’ command (that comes with util-linux), which takes around six minutes for my currently 60% filled 95 GB file system.

Update (2011-07-08): I forgot some details that may be interesting:

  • Kernel version:
  • SSD firmware version: 1.32
  • CPU: AMD Phenom II X4 965

My phone’s bash.profile

Here is some automation that I put into my bash.profile. It’s all done with aliases, since with regular shell scripts, I would first have to remount /mnt/sdcard without ‘noexec’. Like this, I just need to open a ConnectBot “Local” connection, type the alias, and press enter(*).

(*) For this to work, the ‘post login automation’ entry of the ConnectBot “Local” profile needs to have
bash --rcfile /sdcard/bash.profile
in it.

Here is what I have in there:

alias bb="busybox"
alias top="bb top"
alias df="bb df"

alias ll="ls -l"
alias n="su -c \"netstat -ntupl\""

alias backupdata="su -c \"rsync -rP --delete --numeric-ids --chmod=u+rwX --exclude Music /sdcard/ pat@\""

alias postflash="echo \"Mounting /system read-write\" && su -c \"mount -o rw,remount /system\" && echo \"Copying modified keyboard layout files...\" && su -c \"cp /sdcard/vision-keypad-wwe.kcm.bin /system/usr/keychars/\" && su -c \"cp /sdcard/vision-keypad-wwe.kl /system/usr/keylayout/\" && echo \"Deleting awful camera click sound...\" && su -c \"rm /system/media/audio/ui/camera_click.ogg\" && sync && echo \"All done. Please reboot now.\""


The first couple of aliases should be self-explanatory.
backupdata is, as the name suggests, to get my SD card’s content to my home server.
postflash is for after flashing a new ROM (usually a CyanogenMod nightly build). It gets my modified keyboard layout into place, and deletes the terrible sound file that gets played when I take a photo with the phone’s camera.