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 0.2.3
Contents
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 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.
Installation
Install e4ratAUR from the AUR.
Getting it to work
Now for the nitty-gritty:
e4rat-collect
To have e4rat collect a list of files you will need to append init=/sbin/e4rat-collect
to your kernel parameters. For example:
kernel /vmlinuz-linux 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:
e4rat-collect -k
or
pkill e4rat-collect
Upon successful boot and after having waited the allotted time you should see the file /var/lib/e4rat/startup.log
.
Do not forget to remove the e4rat-collect command from your boot loader configuration file[broken link: invalid section] (not necessary if you inserted it on the grub command line).
e4rat-realloc
Once e4rat-collect has finished to run, 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.
Switching to rescue mode with systemctl isolate rescue
(Systemd#Targets table[broken link: invalid section]) may allow for more inodes/blocks to be reallocated as some may not be free while in multiuser.target
e4rat-preload
Append init=/sbin/e4rat-preload
permanently to your kernel parameters.
Alternative: e4rat-preload-lite
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
- 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[broken link: archived in aur-mirror] from the AUR.
Append (or replace) init=/usr/sbin/e4rat-preload-lite
permanently to your kernel parameters. Reboot and enjoy.
e4rat and init systems
e4rat-collect defaults to replacing itself with /sbin/init
upon completion. With the default systemd
installation, this file is a symbolic link to /lib/systemd/systemd
. If you need to specify another process with PID 1, such as /usr/bin/busybox
, you can change this in /etc/e4rat.conf
by setting the init
parameter:
init /usr/bin/busybox
This allows to launch both e4rat-preload
and bootchart
in the same boot sequence.
e4rat-lite
An alternative to e4rat with some improvements made. It is also expected to circumvent some issues one may experience with the original e4rat package. It can be acquired from e4rat-lite-gitAUR
Using e4rat-lite
The commands for e4rat-lite work identically to e4rat. The only differences are the paths to them.
collect: init=/usr/bin/e4rat-lite-collect
realloc: /usr/bin/e4rat-lite-realloc
preload: init=/usr/bin/e4rat-preload
Bootchart
Bootchart can be used to generate graphs of the system startup. This is useful to get visual representations of the CPU and Disk usages. While not required, a before and after comparison of the boot process can be obtained using Bootchart.
bootchart
This version of bootchart automatically stops logging as soon as a display manager comes up. Supposedly the following overrides that and continues logging but it does not 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 bootchart2AUR working together with e4rat edit /sbin/bootchartd2
and replace the line where it says
init="/sbin/init"
with
init="/sbin/e4rat-preload"
This will allow you to measure your boot time with the information that Bootchart2 provides.
It's easy to set up when to stop bootchart2 (contrary to bootchart) by editing its configuration file /etc/bootchartd2.conf
. The line
EXIT_PROC="kdm_greet xterm konsole gnome-terminal metacity mutter compiz ldm icewm-session enlightenment"
can be configured to stop Bootchart2 logging when the specified application launches. Alternatively it may be left empty for the logging to be stopped manually.
To generate the chart, run the command: pybootchartgui -i
Troubleshooting
If things do not work you may want to try the following.
startup.log is not created
- Disable auditd service
- Check the following for any hints
dmesg | grep e4rat
- Try to increase verbosity and loglevel to 31 in your
e4rat.conf
- Try using e4rat-lite instead of e4rat
e4rat erroneously reports an ext2 files system
Add 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:
startup_log_file /etc/e4rat/startup.log
Remove annoying message that mess up boot message
If you are annoyed by the e4rat-preload message during boot, decrease verbose to 1 in /etc/e4rat.conf