E4rat

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e4rat stands for e4 'reduced access time' (ext4 file system only) and is a project by Andreas Rid and Gundolf Kiefer. The e4rat range of tools are comprised of e4rat-collect, e4rat-realloc and e4rat-preload.

Current version is 0.2.1

Process

If you look at a classical bootchart you will notice that neither disk nor CPU are utilized fully during the boot process. e4rat changes this to make full use of both disk and CPU during boot process and thus reduce boot time drastically. It consists of three stages:

  • e4rat-collect - collect files for a specified time (default 120 seconds but this can be adjusted)
  • e4rat-realloc - reallocate files
  • e4rat-preload - preload them

Who benefits, who doesn't

e4rat has proven to be extremely effective for typical single user set-ups which boot straight into X, perhaps even with a number of programs open. If you have a server set-up and boot only into the CLI your boot time decrease may not be as drastic. SSD drives do not benefit because there are no moving parts and thus (almost) no disk latency.

The following might have been valid for version 0.20. We are now at version 0.21 - please report findings for the latest version.

Caveat emptor: the current version of e4rat (0.20) will severely damage any partition that has been converted to ext4. This is likely because existing files are not converted to use extents, and e4rat has no built-in mechanism to detect this condition. Before using e4rat you should backup the affected partitions, reformat them as ext4 and then restore the backups. Given the current status and the nature of the program, it's a smart move to backup the system before attempting reallocation anyway.

Installation

The e4rat package can be found in the [community] repository:

# pacman -S e4rat

Getting it to work

Now for the nitty-gritty:

e4rat-collect

To have e4rat collect a list of files you will need to append the following to your linux line in your /boot/grub/menu.lst (grub legacy) or /boot/grub/grub.cfg (grub2) file:

init=/sbin/e4rat-collect

This will only have to be done once so you may prefer to append this command on the grub command line itself.

Upon booting e4rat-collect will watch your system for a default of 120 seconds. So if you boot, log into X, open your favourite browser and email client all within 2 minutes, every one of those activities is logged. To change the default of 120 seconds edit /etc/e4rat.conf. To manually stop e4rat-collect type:

e4rat-collect -k
or
pkill e4rat-collect

Upon successful boot and after having waited the allotted time you should see the following file: /var/lib/e4rat/startup.log

Do not forget to remove the e4rat-collect command from your menu.lst or grub.cfg file (not necessary if you inserted it on the grub command line).

e4rat-realloc

For the reallocation process change to init 1

sudo init 1

Log in as root and run:

e4rat-realloc  /var/lib/e4rat/startup.log

This can take a while depending on how many files you have in your startup.log file.

e4rat-preload

Append the following permanently to your kernel line in your /boot/grub/menu.lst (grub legacy) or /boot/grub/grub.cfg (grub2) file:

init=/sbin/e4rat-preload

Alternative: e4rat-preload-lite

An alternative preload binairy has been developed by jlindgren, it shaves a few extra seconds from your boot time.

The savings come from

  • using pure C with no external library dependencies, which drops the number of linked .so files from 22 to 3, and
  • preloading only the first 100 files (both inodes and file contents) before starting /sbin/init, then continuing to load the remaining files in parallel with the normal boot sequence.

You can install e4rat-preload-liteAUR from the AUR.

Append (or replace) the following permanently to your kernel line in your /boot/grub/menu.lst (grub legacy) or /boot/grub/grub.cfg (grub2) file:

init=/usr/sbin/e4rat-preload-lite

Reboot and enjoy.

e4rat with different init system

e4rat-collect defaults to replacing itself with /sbin/init upon completion. If you need to specify another PID 1, such as /bin/systemd, you can change this in /etc/e4rat.conf by setting the init parameter and uncommenting the line.

Bootchart

Note: this hasn't worked for and is still in development - any suggestions welcome

You will see a noticeable improvement but nothing can beat a nice Bootchart. Have it run before and after e4rat installation and gawk at the difference.

bootchart 0.9-9

This version automatically stops logging as soon as ?dm comes up. Supposedly the following overrides that and continues logging but it doesn't work for me:

To continue logging adjust your /etc/bootchartd.conf as follows:

AUTO_STOP_LOGGER="no"

To stop it manually type:

~# bootchartd stop

To run both e4rat-preload and bootchart append the following to your grub kernel line:

init=/sbin/bootchartd bootchart_init=/sbin/e4rat-preload

bootchart2

To get bootchart2 working together with e4rat edit /sbin/bootchartd and replace the line init="/sbin/init" with "init="/sbin/e4rat-preload".

/etc/bootchartd.conf of bootchart2 is set up differently and the line

EXIT_PROC="kdm_greet xterm konsole gnome-terminal metacity mutter compiz ldm icewm-session enlightenment"

can be adjusted or left empty for logging to be stopped manually rather than at a predetermined programme start.

Troubleshooting

If things do not work you may want to try the following.

startup.log is not created

  • comment out auditd from your rc.conf
  • check the following for any hints
dmesg | grep e4rat
  • try to increase verbosity and loglevel to 31 in your e4rat.conf

e4rat erroneously reports an ext2 files system

  • add the following to the kernel line in your grub.cfg or menu.lst
rootfstype=ext4

/var/lib/e4rat/startup.log is not accessible

  • this suggests that you have /var on a separate partition which is not yet mounted during boot. You need move your startup.log to an accessible partition (/etc/e4rat/ is just fine) and adjust your /etc/e4rat.conf to reflect this change:
startup_log_file /etc/e4rat/startup.log