Re: Ubuntu 12.04 Highly Compressed Free Download
Edel Dieringer
It was discovered that Pillow incorrectly handled the deletion of temporary
files when using a temporary directory that contains spaces. An attacker could
possibly use this issue to delete arbitrary files. This issue only affected
Ubuntu 20.04 LTS. (CVE-2022-24303)
It was discovered that Pillow incorrectly handled the decompression of highly
compressed GIF data. An attacker could possibly use this issue to cause Pillow
to crash, resulting in a denial of service. (CVE-2022-45198)
Ubuntu is a community developed, linux-based operating system that is perfect for laptops, desktops and servers. It contains all the applications you need - a web browser, presentation, document and spreadsheet software, instant messaging and much more. With Ubuntu Desktop Edition you can surf the web, read email, create documents and spreadsheets, edit images and much more. Ubuntu has a fast and easy graphical installer right on the Desktop CD. On a typical computer the installation should take you less than 25 minutes. When you start your system for the first time you'll see a desktop that is clean and tidy, no desktop icons, and a default theme that is easy on the eye.
Ubuntu uses GNOME as its default desktop environment, intended to provide a free, simple and intuitive interface. Whilst offering a full range of desktop applications including OpenOffice.org, Mozilla Firefox and GIMP, it aims to avoid overlap in its default feature set rather than providing many different variants of similar packages. After the initial Ubuntu installation, the user is greeted by a default desktop with no desktop icons and an orange-brown user interface, unusual in an operating system as nearly all others use blue as their default color. Applications are located under the 'Applications menu', a desktop launcher menu in the top-left corner. Open windows can be viewed on the taskbar along the bottom of the screen. Ubuntu is available in over 40 languages, and also allows users to submit additional translations using the Rosetta Translation tool.
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Squashfs is a highly compressed read-only filesystem for Linux. It uses zlib
compression to compress both files, inodes and directories. Inodes in the
system are very small and all blocks are packed to minimise data overhead.
Block sizes greater than 4K are supported up to a maximum of 64K.
.
Squashfs is intended for general read-only filesystem use, for archival use
(i.e. in cases where a .tar.gz file may be used), and in constrained block
device/memory systems (e.g. embedded systems) where low overhead is needed.
I am testing a new ZFS configuration with z-std for log storage and storage of highly compressible files.The Array is tested on a 5 drive raidz-1 in a virtual machine on my PC which has direct access to the whole HDDs.
I guess writes are being captured in a TXG, compressed, and then committed to disk.But there is some downtime when the CPU is essentially idle and the HDDs themselves are also not really utilized (which is expected, as CPU is the bottleneck when compressing data).
Can I somehow tune ZFS so that it accepts new data while a TXG is being compressed? Or is this the intented, optimal behaviour? If feel like speeds could be better when ZFS constantly accepts and compresses data.
Transactions are aggregated into transactions group (TXG), and up to three TXGs can be "running" at the same time: a first in the open state (accepting writes), a second in the quiescing state (closing accepted writes) and a third in the flush phase (ie: writing to disk). In other words, ZFS does not accept writes "each 5 seconds" only as you seems to describe; rather, it flushes data each 5 seconds unless an high write load is active.
I have a quite large ascii point file containing 3 columns (x and y projected coordinates and the point ID). A test file is about 20MB, containing approximately 600000 points, but I plan to create even larger files with significantly more points. After writing those files to ascii, I'm searching for a way (i.e. file format) to store the data more effectively while still allowing for the following two tasks:
As Luke suggested (What format to use for highly compressed vector data?) I tried SpatiaLite with compressed geometry:ogr2ogr -f SQLite -dsco SPATIALITE=YES -lco COMPRESS_GEOM=YES -lco COMPRESS_COLUMNS=x,y,id points.sqlite points.vrt but the result was a 90MB file (compared to 14MB of the now slightly modified CSV-Input).
Playing around a bit showed, that leaving away the -lco COMPRESS_* did not have any effect on the 90MB file size. Instead, leaving away -dsco SPATIALITE=YES resulted in a 26MB file (I know, this is not SpatiaLite any more). I'm working on Ubuntu 14.04. GDAL 2.1.0 was installed using the UbuntuGIS-PPA. Is there any additional package (besides libspatialite5 v4.1.1) necessary to enable compression in SpatiaLite?
This is just weird. It could be something Debian-specific, but that's just speculation at that point. I need to check a proper Debian Live or Debian desktop or something, and find out. Then I can compare the apt.conf files from Ubuntu 20.04 and Debian Buster, and maybe find a solution for this problem on Armbian.
Can anyone verify if commenting that out gets rid of LZ4 compression for APT? I already have the uncompressed solution above working for me, but maybe I can eventually test in the future to see if logrotate is causing any issues.
On a rockpi 4 I found that switching from lz4 to gz by itself didn't make much of a difference, but disabling compressed indices altogether in /etc/apt/apt.conf.d/02-armbian-compress-indexes and deleting all the lz4 and gz files from /var/lib/apt/lists/ did the trick for me. I'll happily give up a bit of disk space for the interactive performance for now.
I didn't dig into the code yet (and maybe this is already obvious to some) but I suspect this is a mix of unoptimized code paths when dealing with compressed files as well as maybe differences in instruction set extentions between systems. With the default buster settings, this slow behavior occurs on all my arm systems except for a clearfog base which has the notable differences of not being aarch64 and including some handy instruction set extensions that aren't always present on other boards: half thumb fastmult vfp edsp thumbee neon vfpv3 tls vfpd32
When I strace one of the "search" operations, I see a pattern that just doesn't look right... I see lots of repeated "openat" syscalls for the same files over and over along with "reads" for the same blocks of data. Over time, the reads expand to read additional data - but they always follow reading the same data over and over again. It smells to me like whatever method is being used by apt to iterate through these compressed files is resulting in some _very_ inefficient file access patterns. None of this translates to any noticeable hit on the disks because the filesystem cache works well and so all you see is user cpu thrashing one core.
With LZ4-compressed lists, running an apt search on my Rock64 currently takes at least 20 minutes. As other users have reported, it appears to be bottlenecked by CPU, and is not saturating the storage I/O. Needless to say, this is not a usable speed.
Based on what I've found, I believe with substantial confidence that there is no performance problem with LZ4. This should not be too much of a surprise, because speed, especially decompression speed, is LZ4's primary objective; it is in fact considerably faster than LZO in that regard, which means that it's dramatically faster than DEFLATE (gzip). I cannot imagine any conceivable case where switching from LZ4 to DEFLATE would result in decompression performance improvements, and indeed it does not seem to do so here.
In any case, you can trivially see this for yourself by using the command-line lz4 utility to decompress one of the compressed list files in /var/lib/apt/lists. On my Rock64, decompressing the largest of these (/var/lib/apt/lists/apt.armbian.com_dists_buster_main_binary-arm64_Packages.lz4, which weighs about 1.8 MB) takes around a tenth of a second. For some perspective, my test run of an apt search took just over 2700 seconds, so if it did spend all or most of this time doing LZ4 decompression, then it could easly have decompressed every list in the directory over a thousand times each. I am not an expert on the intricacies of file compressors, but I find it to be highly unlikely that LZ4 is responsible for the slowness we're seeing here.
I had a look at the strace output for the search operation. I'm new to reading straces, but I think I can confirm what a previous poster said, which is that it's accessing the same files over and over again with small reads, often many times in the same place. It is unclear to me what function this serves, but this appears to be what takes up the majority of the runtime. If you would like to see for yourself, I've made the full strace output available at _apt-search_armbian.7z. Be warned that it's around 260 megabytes when uncompressed, but since it's extremely repetitive, it compresses efficiently, and the 7z archive is only about 96 kB. In addition, you may compare this to the strace of a sane apt-search operation that I took on an x86 laptop running Debian Bullseye with gzip-compressed package lists, available at _apt-search_debian86.txt (116 kB, not compressed). This isn't much more than a guess, but I wonder if apt is decompressing the entire list with each one of these repeated read operations - this would explain not only the slowness, but also why switching to uncompressed lists seems to help (since it allows the storage cache to render the repeated accesses cheap).
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