Ureadahead

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Revision as of 15:06, 15 August 2010 by Zom (Talk | contribs) (Helping out)

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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.

Requirements

Currently, ureadahead needs a kernel patch to work. This is provided by ying in the AUR.

Ureadahead is also 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 it's 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. Then you need to generate the pack files by running

$ ureadahead --timeout=300

This lets ureadahead trace the boot process for 5 minutes before killing the trace and generating the pack files.

When you've generated the packfiles, you need to start ureadahead during 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. If you want to retrance the boot sequence (After installing new daemons or after upgrading the kernel) you can use

$ ureadahead --timeout=300 --force-trace

It can also be called with

$ ureadahead /<mountpoint>

to generate a packfile for that particular mountpoint. This is useful if you have /usr or /var on separate partitions. Combine it with --timeout to automatically kill the tracing, or just use ^C.

Questions

Template:FAQ Template:FAQ

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

ureadahead homepage

ureadahead package on AUR

patched kernel26 on AUR

Nvidia driver for the patched kernel

kernel patch for compiling your own kernel