etbe - Russell Coker

HP ML350P Gen8

I’m playing with a HP Proliant ML350P Gen8 server (part num 646676-011). For HP servers “ML” means tower (see the ProLiant Wikipedia page for more details [1]). For HP servers the “generation” indicates how old the server is, Gen8 was announced in 2012 and Gen10 seems to be the current generation.

Debian Packages from HP

wget -O /usr/local/hpePublicKey2048_key1.pub https://downloads.linux.hpe.com/SDR/hpePublicKey2048_key1.pub
echo "# HP RAID" >> /etc/apt/sources.list
echo "deb [signed-by=/usr/local/hpePublicKey2048_key1.pub] http://downloads.linux.hpe.com/SDR/downloads/MCP/Debian/ buster/current non-free" >> /etc/apt/sources.list

The above commands will setup the APT repository for Debian/Buster. See the HP Downloads FAQ [2] for more information about their repositories.

hponcfg

This package contains the hponcfg program that configures ILO (the HP remote management system) from Linux. One noteworthy command is “hponcfg -r” to reset the ILO, something you should do before selling an old system.

ssacli

This package contains the ssacli program to configure storage arrays, here are some examples of how to use it:

# list controllers and show slot numbers
ssacli controller all show
# list arrays on controller identified by slot and give array IDs
ssacli controller slot=0 array all show
# show details of one array
ssacli controller slot=0 array A show
# show all disks on one controller
ssacli controller slot=0 physicaldrive all show
# show config of a controller, this gives RAID level etc
ssacli controller slot=0 show config
# delete array B (you can immediately pull the disks from it)
ssacli controller slot=0 array B delete
# create an array type RAID0 with specified drives, do this with one drive per array for BTRFS/ZFS
ssacli controller slot=0 create type=arrayr0 drives=1I:1:1

When a disk is used in JBOD mode just under 33MB will be used at the end of the disk for the RAID metadata. If you have existing disks with a DOS partition table you can put it in a HP array as a JBOD and it will work with all data intact (GPT partition table is more complicated). When all disks are removed from the server the cooling fans run at high speed, this would be annoying if you wanted to have a diskless workstation or server using only external storage.

ssaducli

This package contains the ssaducli diagnostic utility for storage arrays. The SSD “wear gauge report” doesn’t work for the 2 SSDs I tested it on, maybe it only supports SAS SSDs not SATA SSDs. It doesn’t seem to do anything that I need.

storcli

This package contains both 32bit and 64bit versions of the MegaRAID utility and deletes whichever one doesn’t match the installation in the package postinst, so it fails debsums checks etc. The MegaRAID utility is for a different type of RAID controller to the “Smart Storage Array” (AKA SSA) that the other utilities work with. As an aside it seems that there are multiple types of MegaRAID controller, the management program from the storcli package doesn’t work on a Dell server with MegaRAID. They should have made separate 32bit and 64bit versions of this package.

Recommendations

Here is HP page for downloading firmware updates (including security updates) [3], you have to login first and have a warranty. This is legal but poor service. Dell servers have comparable prices (on the second hand marker) and comparable features but give free firmware updates to everyone. Dell have overall lower quality of Debian packages for supporting utilities, but a wider range of support so generally Dell support seems better in every way. Dell and HP hardware seems of equal quality so overall I think it’s best to buy Dell.

Suggestions for HP

Finding which of the signing keys to use is unreasonably difficult. You should get some HP employees to sign the HP keys used for repositories with their personal keys and then go to LUG meetings and get their personal keys well connected to the web of trust. Then upload the HP keys to the public key repositories. You should also use the same keys for signing all versions of the repositories. Having different keys for the different versions of Debian wastes people’s time.

Please provide firmware for all users, even if they buy systems second hand. It is in your best interests to have systems used long-term and have them run securely. It is not in your best interests to have older HP servers perform badly.

Having all the fans run at maximum speed when power is turned on is a standard server feature. Some servers can throttle the fan when the BIOS is running, it would be nice if HP servers did that. Having ridiculously loud fans until just before GRUB starts is annoying.

IMA/EVM Certificates

I’ve been experimenting with IMA/EVM. Here is the Sourceforge page for the upstream project [1]. The aim of that project is to check hashes and maybe public key signatures on files before performing read/exec type operations on them. It can be used as the next logical step from booting a signed kernel with TPM. I am a long way from getting that sort of thing going, just getting the kernel to boot and load keys is my current challenge and isn’t helped due to the lack of documentation on error messages. This blog post started as a way of documenting the error messages so future people who google errors can get a useful result. I am not trying to document everything, just help people get through some of the first problems.

I am using Debian for my work, but some of this will apply to other distributions (particularly the kernel error messages). The Debian distribution has the ima-evm-utils but no other support for IMA/EVM. To get this going in Debian you need to compile your own kernel with IMA support and then boot it with kernel command-line options to enable IMA, in recent kernels that includes “lsm=integrity” as a mandatory requirement to prevent a kernel Oops after mounting the initrd (there is already a patch to fix this).

If you want to just use IMA (not get involved in development) then a good option would be to use RHEL (here is their documentation) [2] or SUSE (here is their documentation) [3]. Note that both RHEL and SUSE use older kernels so their documentation WILL lead you astray if you try and use the latest kernel.org kernel.

The Debian initrd

I created a script named /etc/initramfs-tools/hooks/keys with the following contents to copy the key(s) from /etc/keys to the initrd where the kernel will load it/them. The kernel configuration determines whether x509_evm.der or x509_ima.der (or maybe both) is loaded. I haven’t yet worked out which key is needed when.

#!/bin/bash

mkdir -p ${DESTDIR}/etc/keys
cp /etc/keys/* ${DESTDIR}/etc/keys

Making the Keys

#!/bin/sh

GENKEY=ima.genkey

cat << __EOF__ >$GENKEY
[ req ]
default_bits = 1024
distinguished_name = req_distinguished_name
prompt = no
string_mask = utf8only
x509_extensions = v3_usr

[ req_distinguished_name ]
O = `hostname`
CN = `whoami` signing key
emailAddress = `whoami`@`hostname`

[ v3_usr ]
basicConstraints=critical,CA:FALSE
#basicConstraints=CA:FALSE
keyUsage=digitalSignature
#keyUsage = nonRepudiation, digitalSignature, keyEncipherment
subjectKeyIdentifier=hash
authorityKeyIdentifier=keyid
#authorityKeyIdentifier=keyid,issuer
__EOF__

openssl req -new -nodes -utf8 -sha1 -days 365 -batch -config $GENKEY \
                -out csr_ima.pem -keyout privkey_ima.pem
openssl x509 -req -in csr_ima.pem -days 365 -extfile $GENKEY -extensions v3_usr \
                -CA ~/kern/linux-5.11.14/certs/signing_key.pem -CAkey ~/kern/linux-5.11.14/certs/signing_key.pem -CAcreateserial \
                -outform DER -out x509_evm.der

To get the below result I used the above script to generate a key, it is the /usr/share/doc/ima-evm-utils/examples/ima-genkey.sh script from the ima-evm-utils package but changed to use the key generated from kernel compilation to sign it. You can copy the files in the certs directory from one kernel build tree to another to have the same certificate and use the same initrd configuration. After generating the key I copied x509_evm.der to /etc/keys on the target host and built the initrd before rebooting.

[    1.050321] integrity: Loading X.509 certificate: /etc/keys/x509_evm.der
[    1.092560] integrity: Loaded X.509 cert 'xev: etbe signing key: 99d4fa9051e2c178017180df5fcc6e5dbd8bb606'

Errors

Here are some of the kernel error messages I received along with my best interpretation of what they mean.

[ 1.062031] integrity: Loading X.509 certificate: /etc/keys/x509_ima.der
[ 1.063689] integrity: Problem loading X.509 certificate -74

Error -74 means -EBADMSG, which means there’s something wrong with the certificate file. I have got that from /etc/keys/x509_ima.der not being in der format and I have got it from a der file that contained a key pair that wasn’t signed.

[    1.049170] integrity: Loading X.509 certificate: /etc/keys/x509_ima.der
[    1.093092] integrity: Problem loading X.509 certificate -126

Error -126 means -ENOKEY, so the key wasn’t in the file or the key wasn’t signed by the kernel signing key.

[    1.074759] integrity: Unable to open file: /etc/keys/x509_evm.der (-2)

Error -2 means -ENOENT, so the file wasn’t found on the initrd. Note that it does NOT look at the root filesystem.

References

Basics of Linux Kernel Debugging

Firstly a disclaimer, I’m not an expert on this and I’m not trying to instruct anyone who is aiming to become an expert. The aim of this blog post is to help someone who has a single kernel issue they want to debug as part of doing something that’s mostly not kernel coding. I welcome comments about the second step to kernel debugging for the benefit of people who need more than this (which might include me next week). Also suggestions for people who can’t use a kvm/qemu debugger would be good.

Below is a command to run qemu with GDB. It should be run from the Linux kernel source directory. You can add other qemu options for a blog device and virtual networking if necessary, but the bug I encountered gave an oops from the initrd so I didn’t need to go further. The “nokaslr” is to avoid address space randomisation which deliberately makes debugging tasks harder (from a certain perspective debugging a kernel and compromising a kernel are fairly similar). Loading the bzImage is fine, gdb can map that to the different file it looks at later on.

qemu-system-x86_64 -kernel arch/x86/boot/bzImage -initrd ../initrd-$KERN_VER -curses -m 2000 -append "root=/dev/vda ro nokaslr" -gdb tcp::1200

The command to run GDB is “gdb vmlinux“, when at the GDB prompt you can run the command “target remote localhost:1200” to connect to the GDB server port 1200. Note that there is nothing special about port 1200, it was given in an example I saw and is as good as any other port. It is important that you run GDB against the “vmlinux” file in the main directory not any of the several stripped and packaged files, GDB can’t handle a bzImage file but that’s OK, it ends up much the same in RAM.

When the “target remote” command is processed the kernel will be suspended by the debugger, if you are looking for a bug early in the boot you may need to be quick about this. Using “qemu-system-x86_64” instead of “kvm” slows things down and can help in that regard. The bug I was hunting happened 1.6 seconds after kernel load with KVM and 7.8 seconds after kernel load with qemu. I am not aware of all the implications of the kvm vs qemu decision on debugging. If your bug is a race condition then trying both would be a good strategy.

After the “target remote” command you can debug the kernel just like any other program.

If you put a breakpoint on print_modules() that will catch the operation of printing an Oops which can be handy.

Update: Address Space Randomisation

(gdb) b setxattr
Breakpoint 1 at 0xffffffff81332bf0: file fs/xattr.c, line 546.
(gdb) c
Continuing.
Warning:
Cannot insert breakpoint 1.
Cannot access memory at address 0xffffffff81332bf0

If you get an error like the above while trying to set a breakpoint then it’s probably Address Space Randomisation (known as “KASLR”). Put the parameter “nokaslr” on the kernel command line to stop this. Note that KASLR is a REALLY good thing to have in a normal system as it makes attacks on the kernel security a lot harder, only do this for debugging purposes.

Update: Breakpoints Not Applied

If your gdb session is using a vmlinux that doesn’t match the kernel booted in the VM then things will appear to work, breakpoints can be set, but the running kernel will never break (presumably it would break on some other random kernel code that has the same addresses as the requested function in the other kernel).

So if breakpoints mysteriously don’t work double check that you have a matching vmlinux for the kernel being debugged.

Yama

I’ve just setup the Yama LSM module on some of my Linux systems. Yama controls ptrace which is the debugging and tracing API for Unix systems. The aim is to prevent a compromised process from using ptrace to compromise other processes and cause more damage. In most cases a process which can ptrace another process which usually means having capability SYS_PTRACE (IE being root) or having the same UID as the target process can interfere with that process in other ways such as modifying it’s configuration and data files. But even so I think it has the potential for making things more difficult for attackers without making the system more difficult to use.

If you put “kernel.yama.ptrace_scope = 1” in sysctl.conf (or write “1” to /proc/sys/kernel/yama/ptrace_scope) then a user process can only trace it’s child processes. This means that “strace -p” and “gdb -p” will fail when run as non-root but apart from that everything else will work. Generally “strace -p” (tracing the system calls of another process) is of most use to the sysadmin who can do it as root. The command “gdb -p” and variants of it are commonly used by developers so yama wouldn’t be a good thing on a system that is primarily used for software development.

Another option is “kernel.yama.ptrace_scope = 3” which means no-one can trace and it can’t be disabled without a reboot. This could be a good option for production servers that have no need for software development. It wouldn’t work well for a small server where the sysadmin needs to debug everything, but when dozens or hundreds of servers have their configuration rolled out via a provisioning tool this would be a good setting to include.

See Documentation/admin-guide/LSM/Yama.rst in the kernel source for the details.

When running with capability SYS_PTRACE (IE root shell) you can ptrace anything else and if necessary disable Yama by writing “0” to /proc/sys/kernel/yama/ptrace_scope .

I am enabling mode 1 on all my systems because I think it will make things harder for attackers while not making things more difficult for me.

Also note that SE Linux restricts SYS_PTRACE and also restricts cross-domain ptrace access, so the combination with Yama makes things extra difficult for an attacker.

Yama is enabled in the Debian kernels by default so it’s very easy to setup for Debian users, just edit /etc/sysctl.d/whatever.conf and it will be enabled on boot.

Riverdale

I’ve been watching the show Riverdale on Netflix recently. It’s an interesting modern take on the Archie comics. Having watched Josie and the Pussycats in Outer Space when I was younger I was anticipating something aimed towards a similar audience. As solving mysteries and crimes was apparently a major theme of the show I anticipated something along similar lines to Scooby Doo, some suspense and some spooky things, but then a happy ending where criminals get arrested and no-one gets hurt or killed while the vast majority of people are nice. Instead the first episode has a teen being murdered and Ms Grundy being obsessed with 15yo boys and sleeping with Archie (who’s supposed to be 15 but played by a 20yo actor).

Everyone in the show has some dark secret. The filming has a dark theme, the sky is usually overcast and it’s generally gloomy. This is a significant contrast to Veronica Mars which has some similarities in having a young cast, a sassy female sleuth, and some similar plot elements. Veronica Mars has a bright theme and a significant comedy element in spite of dealing with some dark issues (murder, rape, child sex abuse, and more). But Riverdale is just dark. Anyone who watches this with their kids expecting something like Scooby Doo is in for a big surprise.

There are lots of interesting stylistic elements in the show. Lots of clothing and uniform designs that seem to date from the 1940’s. It seems like some alternate universe where kids have smartphones and laptops while dressing in the style of the 1940s. One thing that annoyed me was construction workers using tools like sledge-hammers instead of excavators. A society that has smart phones but no earth-moving equipment isn’t plausible.

On the upside there is a racial mix in the show that more accurately reflects American society than the original Archie comics and homophobia is much less common than in most parts of our society. For both race issues and gay/lesbian issues the show treats them in an accurate way (portraying some bigotry) while the main characters aren’t racist or homophobic.

I think it’s generally an OK show and recommend it to people who want a dark show. It’s a good show to watch while doing something on a laptop so you can check Wikipedia for the references to 1940s stuff (like when Bikinis were invented). I’m half way through season 3 which isn’t as good as the first 2, I don’t know if it will get better later in the season or whether I should have stopped after season 2.

I don’t usually review fiction, but the interesting aesthetics of the show made it deserve a review.

Storage Trends 2021

The Viability of Small Disks

Less than a year ago I wrote a blog post about storage trends [1]. My main point in that post was that disks smaller than 2TB weren’t viable then and 2TB disks wouldn’t be economically viable in the near future.

Now MSY has 2TB disks for $72 and 2TB SSD for $245, saving $173 if you get a hard drive (compared to saving $240 10 months ago). Given the difference in performance and noise 2TB hard drives won’t be worth using for most applications nowadays.

NVMe vs SSD

Last year NVMe prices were very comparable for SSD prices, I was hoping that trend would continue and SSDs would go away. Now for sizes 1TB and smaller NVMe and SSD prices are very similar, but for 2TB the NVMe prices are twice that of SSD – presumably partly due to poor demand for 2TB NVMe. There are also no NVMe devices larger than 2TB on sale at MSY (a store which caters to home stuff not special server equipment) but SSDs go up to 8TB.

It seems that NVMe is only really suitable for workstation storage and for cache etc on a server. So SATA SSDs will be around for a while.

Small Servers

There are a range of low end servers which support a limited number of disks. Dell has 2 disk servers and 4 disk servers. If one of those had 8TB SSDs you could have 8TB of RAID-1 or 24TB of RAID-Z storage in a low end server. That covers the vast majority of servers (small business or workgroup servers tend to have less than 8TB of storage).

Larger Servers

Anandtech has an article on Seagates roadmap to 120TB disks [2]. They currently sell 20TB disks using HAMR technology

Currently the biggest disks that MSY sells are 10TB for $395, which was also the biggest disk they were selling last year. Last year MSY only sold SSDs up to 2TB in size (larger ones were available from other companies at much higher prices), now they sell 8TB SSDs for $949 (4* capacity increase in less than a year). Seagate is planning 30TB disks for 2023, if SSDs continue to increase in capacity by 4* per year we could have 128TB SSDs in 2023. If you needed a server with 100TB of storage then having 2 or 3 SSDs in a RAID array would be much easier to manage and faster than 4*30TB disks in an array.

When you have a server with many disks you can expect to have more disk failures due to vibration. One time I built a server with 18 disks and took disks from 2 smaller servers that had 4 and 5 disks. The 9 disks which had been working reliably for years started having problems within weeks of running in the bigger server. This is one of the many reasons for paying extra for SSD storage.

Seagate is apparently planning 50TB disks for 2026 and 100TB disks for 2030. If that’s the best they can do then SSD vendors should be able to sell larger products sooner at prices that are competitive. Matching hard drive prices is not required, getting to less than 4* the price should be enough for most customers.

The Anandtech article is worth reading, it mentions some interesting features that Seagate are developing such as having 2 actuators (which they call Mach.2) so the drive can access 2 different tracks at the same time. That can double the performance of a disk, but that doesn’t change things much when SSDs are more than 100* faster. Presumably the Mach.2 disks will be SAS and incredibly expensive while providing significantly less performance than affordable SATA SSDs.

Computer Cases

In my last post I speculated on the appearance of smaller cases designed to not have DVD drives or 3.5″ hard drives. Such cases still haven’t appeared apart from special purpose machines like the NUC that were available last year.

It would be nice if we could get a new industry standard for smaller power supplies. Currently power supplies are expected to be almost 5 inches wide (due to the expectation of a 5.25″ DVD drive mounted horizontally). We need some industry standards for smaller PCs that aren’t like the NUC, the NUC is very nice, but most people who build their own PC need more space than that. I still think that planning on USB DVD drives is the right way to go. I’ve got 4PCs in my home that are regularly used and CDs and DVDs are used so rarely that sharing a single DVD drive among all 4 wouldn’t be a problem.

Conclusion

I’m tempted to get a couple of 4TB SSDs for my home server which cost $487 each, it currently has 2*500G SSDs and 3*4TB disks. I would have to remove some unused files but that’s probably not too hard to do as I have lots of old backups etc on there. Another possibility is to use 2*4TB SSDs for most stuff and 2*4TB disks for backups.

I’m recommending that all my clients only use SSDs for their storage. I only have one client with enough storage that disks are the only option (100TB of storage) but they moved all the functions of that server to AWS and use S3 for the storage. Now I don’t have any clients doing anything with storage that can’t be done in a better way on SSD for a price difference that’s easy for them to afford.

Affordable SSD also makes RAID-1 in workstations more viable. 2 disks in a PC is noisy if you have an office full of them and produces enough waste heat to be a reliability issue (most people don’t cool their offices adequately on weekends). 2 SSDs in a PC is no problem at all. As 500G SSDs are available for $73 it’s not a significant cost to install 2 of them in every PC in the office (more cost for my time than hardware). I generally won’t recommend that hard drives be replaced with SSDs in systems that are working well. But if a machine runs out of space then replacing it with SSDs in a RAID-1 is a good choice.

Moore’s law might cover SSDs, but it definitely doesn’t cover hard drives. Hard drives have fallen way behind developments of most other parts of computers over the last 30 years, hopefully they will go away soon.

Censoring Images

A client asked me to develop a system for “censoring” images from an automatic camera. The situation is that we have a camera taking regular photos from a fixed location which includes part of someone else’s property. So my client made a JPEG with some black rectangles in the sections that need to be covered. The first thing I needed to do was convert the JPEG to a PNG with transparency for the sections that aren’t to be covered.

To convert it I loaded the JPEG in the GIMP and went to the Layer->Transparency->Add Alpha Channel menu to enabled the Alpha channel. Then I selected the “Bucket Fill tool” and used “Mode Erase” and “Fill by Composite” and then clicked on the background (the part of the JPEG that was white) to make it transparent. Then I exported it to PNG.

If anyone knows of an easy way to convert the file then please let me know. It would be nice if there was a command-line program I could run to convert a specified color (default white) to transparent. I say this because I can imagine my client going through a dozen iterations of an overlay file that doesn’t quite fit.

To censor the image I ran the “composite” command from imagemagick. The command I used was “composite -gravity center overlay.png in.jpg out.jpg“. If anyone knows a better way of doing this then please let me know.

The platform I’m using is a ARM926EJ-S rev 5 (v5l) which takes 8 minutes of CPU time to convert a single JPEG at full DSLR resolution (4 megapixel). It also required enabling swap on a SD card to avoid running out of RAM and running “systemctl disable tmp.mount” to stop using tmpfs for /tmp as the system only has 256M of RAM.

Links February 2021

Elestic Search gets a new license to deal with AWS not paying them [1]. Of course AWS will fork the products in question. We need some anti-trust action against Amazon.

Big Think has an interesting article about what appears to be ritualistic behaviour in chompanzees [2]. The next issue is that if they are developing a stone-age culture does that mean we should treat them differently from other less developed animals?

Last Week in AWS has an informative article about Parler’s new serverless architecture [3]. They explain why it’s not easy to move away from a cloud platform even for a service that’s designed to not be dependent on it. The moral of the story is that running a service so horrible that none of the major cloud providers will touch it doesn’t scale.

Patheos has an insightful article about people who spread the most easily disproved lies for their religion [4]. A lot of political commentary nowadays is like that.

Indi Samarajiva wrote an insightful article comparing terrorism in Sri Lanka with the right-wing terrorism in the US [5]. The conclusion is that it’s only just starting in the US.

Belling Cat has an interesting article about the FSB attempt to murder Russian presidential candidate Alexey Navalny [6].

Russ Allbery wrote an interesting review of Anti-Social, a book about the work of an anti-social behavior officer in the UK [7]. The book (and Russ’s review) has some good insights into how crime can be reduced. Of course a large part of that is allowing people who want to use drugs to do so in an affordable way.

Informative post from Electrical Engineering Materials about the difference between KVW and KW [8]. KVA is bigger than KW, sometimes a lot bigger.

Arstechnica has an interesting but not surprising article about a “supply chain” attack on software development [9]. Exploiting the way npm and similar tools resolve dependencies to make them download hostile code. There is no possibility of automatic downloads being OK for security unless they are from known good sites that don’t allow random people to upload. Any sort of system that allows automatic download from sites like the Node or Python repositories, Github, etc is ripe for abuse. I think the correct solution is to have dependencies installed manually or automatically from a distribution like Debian, Ubuntu, Fedora, etc where there have been checks on the source of the source.

Devon Price wrote an insightful Medium article “Laziness Does Not Exist” about the psychological factors which can lead to poor results that many people interpret as “laziness” [10]. Everyone who supervises other people’s work should read this.

Links January 2021

Krebs on Security has an informative article about web notifications and how they are being used for spamming and promoting malware [1]. He also includes links for how to permanently disable them. If nothing else clicking “no” on each new site that wants to send notifications is annoying.

Michael Stapelberg wrote an insightful posts about inefficiencies in the Debian development processes [2]. While I agree with most of his assessment of Debian issues I am not going to decrease my involvement in Debian. Of the issues he mentions the 2 that seem to have the best effort to reward ratio are improvements to mailing list archives (to ideally make it practical to post to lists without subscribing and read responses in the archives) and the issues of forgetting all the complexities of the development process which can be alleviated by better Wiki pages. In my Debian work I’ve contributed more to the Wiki in recent times but not nearly as much as I should.

Jacobin has an insightful article “Ending Poverty in the United States Would Actually Be Pretty Easy” [3].

Mark Brown wrote an interesting blog post about the Rust programming language [4]. He links to a couple of longer blog posts about it. Rust has some great features and I’ve been meaning to learn it.

Scientific America has an informative article about research on the spread of fake news and memes [5]. Something to consider when using social media.

Bruce Schneier wrote an insightful blog post on whether there should be limits on persuasive technology [6].

Jonathan Dowland wrote an interesting blog post about git rebasing and lab books [7]. I think it’s an interesting thought experiment to compare the process of developing code worthy of being committed to a master branch of a VCS to the process of developing a Ph.D thesis.

CBS has a disturbing article about the effect of Covid19 on people’s lungs [8]. Apparently it usually does more lung damage than long-term smoking and even 70%+ of people who don’t have symptoms of the disease get significant lung damage. People who live in heavily affected countries like the US now have to worry that they might have had the disease and got lung damage without knowing it.

Russ Allbery wrote an interesting review of the book “Because Internet” about modern linguistics [9]. The topic is interesting and I might read that book at some future time (I have many good books I want to read).

Jonathan Carter wrote an interesting blog post about CentOS Streams and why using a totally free OS like Debian is going to be a better option for most users [10].

Linus has slammed Intel for using ECC support as a way of segmenting the market between server and desktop to maximise profits [11]. It would be nice if a company made a line of Ryzen systems with ECC RAM support, but most manufacturers seem to be in on the market segmentation scam.

Russ Allbery wrote an interesting review of the book “Can’t Even” about millenials as the burnout generation and the blame that the corporate culture deserves for this [12].

PSI and Cgroup2

In the comments on my post about Load Average Monitoring [1] an anonymous person recommended that I investigate PSI. As an aside, why do I get so many great comments anonymously? Don’t people want to get credit for having good ideas and learning about new technology before others?

PSI is the Pressure Stall Information subsystem for Linux that is included in kernels 4.20 and above, if you want to use it in Debian then you need a kernel from Testing or Unstable (Bullseye has kernel 4.19). The place to start reading about PSI is the main Facebook page about it, it was originally developed at Facebook [2].

I am a little confused by the actual numbers I get out of PSI, while for the load average I can often see where they come from (EG have 2 processes each taking 100% of a core and the load average will be about 2) it’s difficult to work out where the PSI numbers come from. For my own use I decided to treat them as unscaled numbers that just indicate problems, higher number is worse and not worry too much about what the number really means.

With the cgroup2 interface which is supported by the version of systemd in Testing (and which has been included in Debian backports for Buster) you get PSI files for each cgroup. I’ve just uploaded version 1.3.5-2 of etbemon (package mon) to Debian/Unstable which displays the cgroups with PSI numbers greater than 0.5% when the load average test fails.

System CPU Pressure: avg10=0.87 avg60=0.99 avg300=1.00 total=20556310510
/system.slice avg10=0.86 avg60=0.92 avg300=0.97 total=18238772699
/system.slice/system-tor.slice avg10=0.85 avg60=0.69 avg300=0.60 total=11996599996
/system.slice/system-tor.slice/tor@default.service avg10=0.83 avg60=0.69 avg300=0.59 total=5358485146

System IO Pressure: avg10=18.30 avg60=35.85 avg300=42.85 total=310383148314
 full avg10=13.95 avg60=27.72 avg300=33.60 total=216001337513
/system.slice avg10=2.78 avg60=3.86 avg300=5.74 total=51574347007
/system.slice full avg10=1.87 avg60=2.87 avg300=4.36 total=35513103577
/system.slice/mariadb.service avg10=1.33 avg60=3.07 avg300=3.68 total=2559016514
/system.slice/mariadb.service full avg10=1.29 avg60=3.01 avg300=3.61 total=2508485595
/system.slice/matrix-synapse.service avg10=2.74 avg60=3.92 avg300=4.95 total=20466738903
/system.slice/matrix-synapse.service full avg10=2.74 avg60=3.92 avg300=4.95 total=20435187166

Above is an extract from the output of the loadaverage check. It shows that tor is a major user of CPU time (the VM runs a ToR relay node and has close to 100% of one core devoted to that task). It also shows that Mariadb and Matrix are the main users of disk IO. When I installed Matrix the Debian package told me that using SQLite would give lower performance than MySQL, but that didn’t seem like a big deal as the server only has a few users. Maybe I should move Matrix to the Mariadb instance. to improve overall system performance.

So far I have not written any code to display the memory PSI files. I don’t have a lack of RAM on systems I run at the moment and don’t have a good test case for this. I welcome patches from people who have the ability to test this and get some benefit from it.

We are probably about 6 months away from a new release of Debian and this is probably the last thing I need to do to make etbemon ready for that.

etbe – Russell Coker

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