Difference between revisions of "Ureadahead"

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[[Category:Boot process (English)]]
#REDIRECT [[Improving performance/Boot process]]
Ureadahead (Über-readahead) is used to speed up the boot process. It works by reading all the files required during boot and makes pack files for quicker access, then during boot reads these files in advance, thus minimizes the access times for the harddrives. It's intended to replace sreadahead.
== Requirements ==
Currently, ureadahead needs a kernel patch to work. This is provided by ying in the [http://aur.archlinux.org/packages.php?ID=37895 AUR].
Ureadahead is also [http://aur.archlinux.org/packages.php?ID=37889 available], of course.
== How it works ==
When run without any arguments, ureadahead checks for pack files in /var/lib/ureadahead, and if  none are found or if the packfiles are older than a month, it starts tracing the boot process. When tracing, it waits for either a TERM or INT signal before generating the pack file.
Otherwise, if the file is up to date, it just reads the pack file in preparation for the boot.
It works for both SSDs and traditional harddrives and automatically optimizes the pack files depending on which you have.
== Using ureadahead ==
First you need the patched kernel. After the installation you need to make ureadahead start on boot. Simply create the file /etc/rc.d/functions.d/ureadahead and add
ureadahead() {
/sbin/ureadahead --timeout=240 &
add_hook sysinit_end ureadahead
to start it after sysinit.
{{Note|You can also use sysinit_premount to start it before it mounts all the other filesystems in /etc/fstab, but this might create issues depending on your system (e.g. if you have /var on a separate partition).}}
Now you should be good to go.
== Configuration ==
There isn't really much in the way of configuring ureadahead. You can specify which mountpoint to trace with
$ ureadahead /<mountpoint>
though it should automatically trace all needed mountpoints during boot.
You can also run it with --force-trace to force a retrace, however it's better just to remove the pack files and reboot.
The pack files are in /var/lib/ureadahead and are named after their mountpoint (i.e. pack for root, home.pack for /home).
== Questions ==
|question=Why does this take so long time tracing?
|answer=If you didn't supply --timeout, you need to kill it manually. Either just ^C it, or use pkill ureadahead.}}
== Helping out ==
If your boot actually becomes slower after generating the pack files and you're sure ureadahead is to blame, then file a bug report. To get useful data, make sure both ureadahead and bootchart installed.
First, disable ureadahead on boot (remove /etc/rc.d/functions.d/ureadahead) and remove the pack files in /var/lib/ureadahead, then reboot and save the bootchart.
Then, reenable ureadahead (recreate the file in /etc/rc.d/functions.d/ureadahead) and reboot. Save this bootchart too.
Finally, reboot once more, and save the final bootchart.
Now you should have 3 bootcharts, one without ureadahead, one when ureadahead is tracing and one when it's running normally. Then, as root, run
$ ureadahead --dump > ureadahead.dump
to dump the contents of the pack file. Create a bug report on the ureadahead launchpad file and attach the bootcharts along with the dump.
{{Note|I don't know how welcome this will be to the ubuntu developers, since we're using arch. If you still want to help, give it a try and see if they're interested.}}
== More resources ==
*[https://launchpad.net/ubuntu/+source/ureadahead ureadahead homepage]
*[http://aur.archlinux.org/packages.php?ID=37889 ureadahead package on AUR]
*[http://aur.archlinux.org/packages.php?ID=37895 patched kernel26 on AUR]
*[http://aur.archlinux.org/packages.php?ID=37948 Nvidia driver for the patched kernel]
*[http://aur.archlinux.org/packages/kernel26-yi/kernel26-yi/0001-trace-add-trace-events-for-open-exec-an.patch kernel patch for compiling your own kernel]{{Linkrot|2011|09|05}}

Latest revision as of 04:17, 27 August 2016