sabi notesNotes mostly about Linux and computer issuessabicohttp://www.sabi.co.uk/Copyright 2017 Peter G.http://www.sabi.co.uk/2023-01-17T20:00:00ZSo far Firefox 57 "Quantum" is good2017-12-27T17:20:00Z2017-12-27T17:20:00Zhttp://www.sabi.co.uk/blog/171227Having used Firefox 57 "Quantum" for several
weeks, so far it is good, and even an improvement.The "mixin" and "flavors" problem for configuration2017-10-29T17:10:00Z2017-10-29T17:10:00Zhttp://www.sabi.co.uk/blog/171101Software-defined infrastructures are defined by
software, that is by programs or scripts. These programs are
expensive to write and expensive to maintain, even if they are in
theory more flexible than hardware infrastructure. However since
they rely on a fixed hardware infrastructure their actual
flexibility is bounded by that fixed hardware infrastructure, as to
performance at least. Software defined infrastructure work well when
their performance enveloped is rather bigger than that of any
workload they are meant to run, and the programs that deliver the
extra flexibility are written with maintainability in
mind.VM infrastructure skepticism is good for VM infrastructures2017-12-11T18:50:00Z2017-12-11T18:50:00Zhttp://www.sabi.co.uk/blog/171211VM infrastructures have significant tendency to
long term downsides related to complexity and overloading. Systems
engineers that are aware of that tendency are better suited to design
and maintain them because they are more likely to try to slow down
that tendency.Mobile phone network hacking and more on security2017-10-14T15:40:00Z2017-10-14T15:40:00Zhttp://www.sabi.co.uk/blog/171014Even mobile phone networks can be hacked to
work arond two-factor authentication, and even ordinary electrical
devices can be cheaply endowed with spying microdevices, and
large-budget "targeted operations" are difficult to defend
against. Being prudent about them helps, just as it helps to be a
low-value target.Some interesting tools2017-11-17T23:30:00Z2017-11-17T23:30:00Zhttp://www.sabi.co.uk/blog/171117I have recently noticed Greyhole and SnapRAID,
two unusual storage tools, and Singularity, a containerization
scheme.Misconfiguration of SATA chip made flash SSD look slower2017-12-01T23:40:00Z2017-12-01T23:40:00Zhttp://www.sabi.co.uk/blog/171201The halving of the transfer rate of a flash SSD
was not due to its getting older, but to its interface being
switched to SATA1 mode.Some recent news about "security"2017-11-18T12:15:00Z2017-11-18T12:15:00Zhttp://www.sabi.co.uk/blog/171118Various recent computer "hacking" news show
that it is pervasive, and can be profitable. It is important to
avoid being or appearing a profitable target.Switching to Firefox 57 Quantum2017-11-13T18:05:00Z2017-11-13T18:05:00Zhttp://www.sabi.co.uk/blog/171113Switching to Firefox 57 Quantum usually
requires some manual intervention to configure its confinement
sandbox, to preserve the sessions across the upgrade, to limit CPU
and memory consumption by greedy websites, and replace XUL add-ons
with WebExtension ones. The result can be a reasonable
improvement.Status of Btrfs2017-11-09T16:20:00Z2017-11-09T16:20:00Zhttp://www.sabi.co.uk/blog/171109There is now a page of notes dedicated to
Btrfs, with contents extracted from the Linux filesystes notes,
plus a list of Btrfs terms and a summary description of its status
and recommended usage.C vs. C++ and the cost of system level features2017-10-04T17:10:00Z2017-10-04T17:10:00Zhttp://www.sabi.co.uk/blog/171004In C every language feature has a simple and
low cost, while in C++ some features that look simple can have a
large cost. The same happens at the system level, for example with
Btrfs, where some features or combinations of features can have
surprisingly large costs.SFTP speeds have improved a lot2017-08-31T17:50:00Z2017-08-31T17:50:00Zhttp://www.sabi.co.uk/blog/170831SFTP used to be slow as it was almost
half-duplex, better protocol and mostly implementation have made it
good.Complexity and maintainability and virtualization2017-09-18T17:20:00Z2017-09-18T17:20:00Zhttp://www.sabi.co.uk/blog/170918Layers and masses of complexity and some
ready-made collection of scripts result in a working single-host
minimal OpenStack system in 3 half days. Given how complicated it is
that's good, but is the complexity necessary, and how fragile is it
going to be?A developer buys a very powerful laptop2017-09-04T12:50:00Z2017-09-04T12:50:00Zhttp://www.sabi.co.uk/blog/170904A software developer is pleased to have been
able to buy a massively powerful laptop; but I suspect that the
software written on it will not be that fast.Some STREAM and HPL results from some not-so-new systems2017-09-17T20:10:00Z2017-09-17T20:10:00Zhttp://www.sabi.co.uk/blog/170917A minimal speed test of 4 systems with a
variety of not so-new CPUs, 3 from AMD and one from Intel,
using the STREAM and HPL benchmark programs.50TB 3.5in flash SSD2017-08-17T17:15:00Z2017-08-17T17:15:00Zhttp://www.sabi.co.uk/blog/170817Interesting 3.5in 50TB flash SSD product with
dual SAS ports, with somewhat slow write speeds though.M.2 storage with and without backing capacitors2017-08-25T19:10:00Z2017-08-25T19:10:00Zhttp://www.sabi.co.uk/blog/170825M.2 flash SSD sticks like flash SSDs in the
2.5in format also come with capacitors backing cache or
without.Another economic reason to virtualize2017-08-16T21:00:00Z2017-08-16T21:00:00Zhttp://www.sabi.co.uk/blog/170816One of the economic cases for virtualization is
that mid-size hardware servers are more cost effective than smaller
ones, so virtualization allows sharing them among several applications.
However that sharing also has costs, such as overheads and extra
complexity, so the overall balance can be either way. Unless the
consolidation is a way to raise the cost and complexity of hosting
IT application to their users, by shifting more of that cost from
central IT to IT application using budget centres.Speedy writing to a BD-R DL disc2017-08-10T23:45:00Z2017-08-10T23:45:00Zhttp://www.sabi.co.uk/blog/170810Writing at speed to DVD and BD media requires
custom firmware profiles, as it is quite a delicate operation. With
a firmware upgrade it has become possible to write at 8x speed
(around 32MB/s) on my Pioneer BD writer to BD-R DL (50GB) media
which is very convenient for small offline backups.Fixing an Ubuntu phone after a power loss crash2017-07-01T14:05:00Z2017-07-01T14:05:00Zhttp://www.sabi.co.uk/blog/170701Fixing an Ubuntu phone after a power loss crash
required removing some lock files and cleaning a cache.Different types of M.2 slots2017-07-24T23:40:00Z2017-07-24T23:40:00Zhttp://www.sabi.co.uk/blog/170724Mentioned in the product descriptiuon of an
adapter card between an M.2 socket and a PCIe socket that there
are at least three different types of M.2 sockets. A user reports
that with a nice high-end flash SSD they get 2.5GB/s sequential
reads a 1.5GB/s sequential writes, which is notable.Hardware specification of "converged" mobile phone2017-07-16T13:00:00Z2017-07-16T13:00:00Zhttp://www.sabi.co.uk/blog/170716cThe Samsung S8+ not only has a colossal
hardware specification, including a 2960x1440 AMOLED display, it
also has a docking station that allows connecting an external
monitor, keyboard and mouse, realizing for Android the Ubuntu
dream of convergence between mobile phones and desktop computers.Hardware specification of smart watch and related2017-07-16T12:20:00Z2017-07-16T12:20:00Zhttp://www.sabi.co.uk/blog/170716bA "smartwatch" has 1 dual CPU 1GHz chip, 768MiB
of RAM, 4GiB of flash SSD.Miracles do happen: memristor product exists2017-07-16T11:40:00Z2017-07-16T11:40:00Zhttp://www.sabi.co.uk/blog/170716After many years of talk, it is now possible to
buy memristor SSDs. Cost per GiB is 4-8 times higher than for flash
SSDs, transfe rates and endurance are comparable, access times are
however very low, around 10-20 microseconds.Mobile phones with 2560x1440 screens2014-11-08T14:40:00Z2014-11-08T14:40:00Zhttp://www.sabi.co.uk/blog/141108A blog post shows the author deciding between
two top Samsung cellphones with AMOLED screens, one with 1920x1080
and the other with 2560x1440 pixel sizes. There are few laptops with
those pixel sizes, none with OLED screens yet, and no desktop OLED
monitors either.The O_PONIES summary and too much durability2017-07-20T12:40:00Z2017-07-20T12:40:00Zhttp://www.sabi.co.uk/blog/170720A summary of the O_PONIES controversy and an
explanation of why the best strategy is "too much
durability".Special case indentation for PSGML2017-07-12T23:20:00Z2017-07-12T23:20:00Zhttp://www.sabi.co.uk/blog/170712The PSGML packages for EMACS does
structure-based editing of SGML/HTML files, but its default
indentation rules don't allow to specify that the content of some
entities does not need further indentation and the content of some
entities does not need any indentation. A simple customization is
presented that supports both cases.Fast route lookup in Linux with large numbers of routes2017-07-04T21:10:00Z2017-07-04T21:10:00Zhttp://www.sabi.co.uk/blog/170704Recent Linux kernels can lookup a route among
500,000 in less than 40 nanoseconds, making clear that extensive use
of so-called host-routes is quite cheap and Ethernet forwarding no
longer necessary.Remote two factor authentication and passwords and passphrases2017-04-17T12:30:00Z2017-04-17T12:30:00Zhttp://www.sabi.co.uk/blog/170417Some passwords or passphrases in some
circumstances involve effectively two factors, where the second
factor is possession of a physical device or an encrypted file. For
example a login password that cannot be used to login remotely
require physical possession of the target system, and a passphrase
for an encrypted SSH key requires possession of the file containing
the key to achieve remote login. Some possibilities
illustrated.Homogenous systems and heteregenous workloads2016-11-26T15:10:00Z2016-11-26T15:10:00Zhttp://www.sabi.co.uk/blog/161126A scholar who studies HPC cluster memory and
interconnect latencies and bandwidth points out that a generic
cluster cannot run optimally every workloads (and indeed any). The
problem is that most workloads have highly anisotropic performance
envelopes, and a homogenous system has one that is highly
anisotropic too, and only by chances covers well actual
workloads.Unusual filesystem properties2017-04-07T23:10:00Z2017-04-07T23:10:00Zhttp://www.sabi.co.uk/blog/170407In Btrfs the special fixed value of 0 is used
as the link count of any directory, and 0 as the total inode count
of any filetree. These special values mean "not available" and are
not backwards compatible.How challenging is a goal of 18MB/s per TB of storage, and latency2017-06-10T13:00:00Z2017-06-10T13:00:00Zhttp://www.sabi.co.uk/blog/170610On a 1TB it takes an average IO size of around
0.5MB to deliver 18MB/s of interleaved read-write per TB, on a 3TB
disk it takes an average transfer size of 3MB, and on larger disks
it is not possible. That goal seems easy to people used to flash SSDs,
but for hard disks it is quite ambitious.The NSA "hoard" and WannaCry2017-05-14T19:10:00Z2017-05-14T19:10:00Zhttp://www.sabi.co.uk/blog/170514The recent WannaCry ransomware is based on
a trivial exploit on an old version of MS-Windows from an NSA
exploit kit. It only affected a small number of systems. Presumably
the NSA and competitors have much better exploits, but also they
mostly target specific systems.Hard links: not for GNU/Linux GUI users?2017-05-20T13:00:00Z2017-05-20T13:00:00Zhttp://www.sabi.co.uk/blog/170520Several GNU/Linux filemanagers with a GUI
interface don't allow hard-linking files. Apparently this is because
that is considered a concept too advanced for GUI users.Stuck laptop CPU fan and temperatures2017-05-19T23:10:00Z2017-05-19T23:10:00Zhttp://www.sabi.co.uk/blog/170519Cleaning the cooling system of my laptop
made it keep the laptop's CPU largely constant, perhaps because the
CPU fan was stuck by dust. Cleaning the filter grilles of my desktop
case caused the disk temperatures to drop by 3C.Preventing Linux partition scanning2017-05-13T10:20:00Z2017-05-13T10:20:00Zhttp://www.sabi.co.uk/blog/170513A user had the problem that the Linux kernel
would crash on attempting to scan a malformed partition table as
soon as a disk was connected to the system. There may be an
accidental workaround, but the fundamental problem is that Linux
kernel microsoftization means that it ends up attempting to be
too "automagic".Web pages and laptop heat2017-05-06T09:35:00Z2017-05-06T09:35:00Zhttp://www.sabi.co.uk/blog/170506Because of looping JavaScript code in web pages
my laptop has been shutting down a couple of times per week because
of overheating due to sustained high CPU usage.NFS, GNOME and KDE issues with auto-mounting2017-04-27T19:50:00Z2017-04-27T19:50:00Zhttp://www.sabi.co.uk/blog/170427Ideally filetrees would not be auto-mounted
while they are being actively accessed, but the NFS servers and
aspects of KDE and GNOME keep them mounted even when not actively
accessed even when an auto-mounter is used. There are some solutions
though for some cases.Btrfs and NFS service and NFS daemon Ganesha2017-04-24T23:20:00Z2017-04-24T23:20:00Zhttp://www.sabi.co.uk/blog/170424Btrfs does not properly update checksums
during direct-IO writes, and the 'nfs-kernel-server' does
direct-IO. The NFS server Ganesha does not and is used-level,
and has some interesting features, and is simpler to configure,
and I found it quite a good alternative.IPv6 reaches 14% of Google traffic, SixXS will close down2017-03-24T18:00:00Z2017-03-24T18:00:00Zhttp://www.sabi.co.uk/blog/170324IPv6 has grown from 2% of traffic seen by
Google in 2013 to 14%, and mass-market ISPs are providing
native IPv6 connectivity. Accordingly the transition service
provided by SixXS for many years will be shut down.The mainframe development problem and MPI2017-01-29T12:10:00Z2017-01-29T12:10:00Zhttp://www.sabi.co.uk/blog/170129It is difficult to develop for platforms that
are unusual or very expensive because compatible developer
workstations are not easily available or have very different
performance envelopes.Some coarse speed tests with Btrfs etc. and small files2017-03-02T08:20:00Z2017-03-02T08:20:00Zhttp://www.sabi.co.uk/blog/170302Further coarse speed tests of Btrfs and some other
filesystems when writing lots of small files to disk, with and
without 'fsync' at the end of each file.Some coarse speed tests with various Linux filesystems2017-02-28T20:10:00Z2017-02-28T20:10:00Zhttp://www.sabi.co.uk/blog/170228Done a simple coarse test of writing
and reading back from several 1TiB empty filetrees around 600GiB
of data mostly in large files. With Btrfs, F2FS, JFS, NILFS2,
OCFS2, ReiserFS, UDF, XFS, ZFSonLinux. All were fairly adequate
with some interesting variation.F2FS and Bcachefs2017-01-07T19:00:00Z2017-01-07T19:00:00Zhttp://www.sabi.co.uk/blog/170107F2FS is a relatively recent but well supported
and stable mostly log structured filesystem, and Bcachefs is a
personal project of the author of Bcache, and seems quite feature
rich and interesting.The most interesting filesystem types2016-12-17T17:50:00Z2016-12-17T17:50:00Zhttp://www.sabi.co.uk/blog/161217A short discussion of the most useful aspects
of what I reckon are the more interesting Linux filesystem types:
JFS, ReiserFS, NILFS2, XFS, Btrfs, UDF, OCFS2.New Seagate disc drives and their declared duty cycles2017-02-14T17:50:00Z2017-02-14T17:50:00Zhttp://www.sabi.co.uk/blog/170214New Seagate cold storage drives have yearly
usage ratings of 180GB to 550GB.Aggregate cost of AWS servers2017-02-04T14:40:00Z2017-02-04T14:40:00Zhttp://www.sabi.co.uk/blog/170204A BusinessWeek article on cloud storage cost
monitoring reports the aggregate cost and number of cloud systems
for a company. The numbers are large enough that probably they would
save a lot by buying physical infrastructure. Probably it is just
habitual convenience having started with cloud systems when they
were a much smaller company.A straightforward alternative to the setuid mechanism too2017-02-05T21:40:00Z2017-02-05T21:40:00Zhttp://www.sabi.co.uk/blog/170205Having distinct effective (from the parent) and
preventive (from the executable) ids for a process and some simple
rules results in both protection domain crossing like for set-id
and in confinement, and can be fully backards-compatible.A straightforward alternative to confinement mechanisms2017-02-02T17:50:00Z2017-02-02T17:50:00Zhttp://www.sabi.co.uk/blog/170202If Linux processes had both user and program
ids and access was based on both confinement would be simple and
easy.An interesting introduction to namespaces2017-01-28T10:10:00Z2017-01-28T10:10:00Zhttp://www.sabi.co.uk/blog/170128Discovered a fairly useful blog by agency
contractors, and in particular a note introducing Linux namespaces
and how to program for their use, even if bit optimistic on the real
strength of the isolation that they provide.What is the "Internet"?2017-01-20T18:20:00Z2017-01-20T18:20:00Zhttp://www.sabi.co.uk/blog/170120There is a proper technical definition of what
the "Internet" is and is based on IANA conventions and '.gov' site
reachability.