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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
- 1 Process
- 2 Installation
- 3 Getting it to work
- 4 e4rat with different init system, e.g. systemd
- 5 Bootchart
- 6 Troubleshooting
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 does not
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. Users of SSD drives do not benefit because there are no moving parts and thus (almost) no disk latency - Ureadahead might be worth looking at.
It is always better to be safe than sorry. Just make backup if you cannot afford to lose data on your partition.
Getting it to work
Now for the nitty-gritty:
To have e4rat collect a list of files you will need to append
init=/sbin/e4rat-collect to your kernel parameters.For example:
kernel /vmlinuz0linux root=/dev/disk/by-label/ARCH init=/sbin/e4rat-collect ro 5
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:
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 boot loader configuration file (not necessary if you inserted it on the grub command line).
For the reallocation process change to init 1
sudo init 1
Log in as root and run:
This can take a while depending on how many files you have in your startup.log file.
init=/sbin/e4rat-preload permanently to your kernel parameters.
An alternative preload binary has been developed by jlindgren, it saves 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
Note: Current [0.2.2] version of e4rat-preload is linked against 5 .so libraries, including libc, libm, libpthread ! So there is not much of a difference here !
- 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 AUR.AUR from the
Append (or replace)
init=/usr/sbin/e4rat-preload-lite permanently to your kernel parameters. Reboot and enjoy.
e4rat with different init system, e.g. systemd
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. So in spite of
; init /sbin/init
you would have:
This allows to launch both e4rat-preload and bootchart in the same boot sequence.
Note: this has not 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.
To continue logging adjust your /etc/bootchartd.conf as follows:
To stop it manually type:
~# bootchartd stop
To run both e4rat-preload and bootchart append the following to your grub kernel line:
To get bootchart2 working together with e4rat edit /sbin/bootchartd and replace the line where it says
This will allow you to measure your boot time with the fine informations that Bootchart2 provides.
It's easy to set up when to stop bootchart2 (on opposite to bootchat) by editing its configuration file /etc/bootchartd.conf. Simply adjust the line
EXIT_PROC="kdm_greet xterm konsole gnome-terminal metacity mutter compiz ldm icewm-session enlightenment"
with any program you want Bootchart2 stop logging when it launches, or rather left it empty for logging to be stopped manually.
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
rootfstype=ext4 to kernel parameters from your bootloader.
/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:
Remove annoying message that mess up boot message
If you are annoyed by the e4rat-preload message during boot, decrease loglevel to 1 in /etc/e4rat.conf