Difference between revisions of "Ureadahead"

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[[Category:Boot process]]
#REDIRECT [[Improving performance/Boot process]]
{{Note|ureadahead package is orphaned because Systemd comes with its own readahead implementation. See [[Improve Boot Performance#Readahead]].}}
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. You can use {{AUR|linux-ureadahead}}.
The user-space package is called {{AUR|ureadahead}}.
== 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 {{ic|/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 {{ic|sysinit_premount}} to start it before it mounts all the other filesystems in {{ic|/etc/fstab}}, but this might create issues depending on your system (e.g. if you have {{ic|/var}} on a separate partition).}}
Now you should be good to go.
== Configuration ==
There are few configuration options for ureadahead. You can specify which mountpoint to trace with:
{{bc|$ ureadahead /<mountpoint>}}
though it should automatically trace all needed mountpoints during boot.
You can also run it with {{Ic|--force-trace}} to force a retrace, however it is better to remove the pack files and reboot.
The pack files are in {{ic|/var/lib/ureadahead}} and are named after their mountpoint (i.e. {{ic|pack}} for root, {{ic|home.pack}} for {{ic|/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 {{Keypress|^C}} it, or use {{ic|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 {{ic|/etc/rc.d/functions.d/ureadahead}}) and remove the pack files in {{ic|/var/lib/ureadahead}}, then reboot and save the bootchart.
Then, reenable ureadahead (recreate the file in {{ic|/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:
{{bc|# 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 do not 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]
*[https://aur.archlinux.org/packages.php?ID=37889 ureadahead package on AUR]
*[https://aur.archlinux.org/packages.php?ID=37948 Nvidia driver for the patched kernel]

Latest revision as of 04:17, 27 August 2016