Category Archives: linux

7zip compression test of Raspberry backup image

I regularly backup the Raspbian system of my several Raspberry Pi’s, for reasons that anyone owning and using a Raspberry Pi knows.

With time you end up always wanting more, and I want to upload backups on the cloud for that additional layer of extra safety; cloud space, though, is either free and very limited, or quite costly to mantain, hence the smaller the files you upload, the more practical is sending them online.

With this purpose in mind, I wanted to try several compression options, using the same source file (a 3.7GB image file produced by my latest version of RaspiBackup -the “bleeding edge” which right now is in its own branch), but changing some parameters from the default “Ultra settings” (the one you can find in 7z manpage).

All tests were done on a non overclocked Raspberry Pi 4 with 4GB of RAM.

First test goes with the “ultra settings” comandline found in 7z manpage:

time 7z a -t7z -m0=lzma -mx=9 -mfb=64 -md=32m -ms=on archive.7z source.img

7-Zip [32] 16.02 : Copyright (c) 1999-2016 Igor Pavlov : 2016-05-21
p7zip Version 16.02 (locale=en_US.UTF-8,Utf16=on,HugeFiles=on,32 bits,4 CPUs LE)

Scanning the drive:
1 file, 3981165056 bytes (3797 MiB)

Creating archive: archive.7z

Items to compress: 1


Files read from disk: 1
Archive size: 695921344 bytes (664 MiB)
Everything is Ok

real    50m33.638s
user    73m16.589s
sys     0m44.505s

Second test builds on this, and increases the dictionary size to 128MB (which is, alas, the maximum allowed for 32bit systems as per 7zip documentation, any value above this will throw an error on the raspberry):

time 7z a -t7z -m0=lzma -mx=9 -mfb=64 -md=128m -ms=on archive.7z source.img

7-Zip [32] 16.02 : Copyright (c) 1999-2016 Igor Pavlov : 2016-05-21
p7zip Version 16.02 (locale=en_US.UTF-8,Utf16=on,HugeFiles=on,32 bits,4 CPUs LE)

Scanning the drive:
1 file, 3981165056 bytes (3797 MiB)

Creating archive: archive.7z

Items to compress: 1


Files read from disk: 1
Archive size: 625572636 bytes (597 MiB)
Everything is Ok

real    59m54.703s
user    80m50.340s
sys     0m55.886s

Third test puts another variable in the equation, by adding the -mmc=10000 parameter, which tells the algorithm to cycle ten thousand times to find matches in the dictionary, hence increasing the possibility of a better compression, from the default number of cycles which should be in this case less than 100.

time 7z a -t7z -m0=lzma -mx=9 -mfb=64 -md=128m -mmc=10000 -ms=on archive.7z source.img

7-Zip [32] 16.02 : Copyright (c) 1999-2016 Igor Pavlov : 2016-05-21
p7zip Version 16.02 (locale=en_US.UTF-8,Utf16=on,HugeFiles=on,32 bits,4 CPUs LE)

Scanning the drive:
1 file, 3981165056 bytes (3797 MiB)

Creating archive: archive.7z

Items to compress: 1


Files read from disk: 1
Archive size: 625183257 bytes (597 MiB)
Everything is Ok

real    77m53.377s
user    99m48.431s
sys     0m39.215s

I then tried one last command line that I found on Stack Exchange network:

time 7z a -t7z -mx=9 -mfb=32 -ms -md=31 -myx=9 -mtm=- -mmt -mmtf -md=128m -mmf=bt3 -mpb=0 -mlc=0 archive.7z source.img

and I cannot find that answer anymore but it boasted the best compression rate ever (yeah, I imagine, everything was set to potential maximum). This commandline I had to tone down, because it implied increasing to the maximum possibile the dictionary size (which is 1536MB, but it’s not feasible on 32bit system which are limited to 128MB) and also the fast bytes to its maximum of 273.

I always got an error though:

ERROR: Can't allocate required memory!

even by gradually decreasing the -mfb (fast bytes) down to 32; even if I completely removed the fast bytes parameter. At this point I simply desisted.

So, onto the

Conclusions:

You should definitely pump up the dictionary size to its limit of 128MB, because it yields a discrete compression increase (down to 15.7% from 17.5%, so 10% smaller). According to this post the time increase must be measured as “user+sys”), so it’s 74 minutes of CPU time for first example, 81.75 minutes for the second, and 100.5 minutes for the third. The difference in CPU time between the first and second is still in the ballpark of 10%, so that additional time gets practically converted in better compression, I’ll take it.

Interestingly, increasing the matching cycles didn’t bring ANY increase in compression, at the expense of a whopping 25% increase in processing time (actually it did when I compared the exact file sizes, and it was negligible at just a few hundred kilobytes less).

Overall, this is is a great result, as the total free space in that image should be around 300MB, so the rest is all real data compression.

Decode Raspberry vcgencmd get_throttled response with a PHP script

If you search for an interpretation to get a meaning out of the command

vcgencmd get_throttled

which might return something like:

throttled=0x50005

you will find many forum posts that basically tell you it is a bitcode and that you have to decode it following this table:

Bit Meaning
0 Under-voltage detected
1 Arm frequency capped
2 Currently throttled
3 Soft temperature limit active
16 Under-voltage has occurred
17 Arm frequency capped has occurred
18 Throttling has occurred
19 Soft temperature limit has occurred

(from this GitHub page)

yyyyeaaahhhh right.

Finally I found a comprehensible explanation here and I decided to write a script around it, and since I know PHP this is what I used.

So, from your home folder,

nano throttled.php

paste this inside:

<?php
$codes=array(
0=>"Under-voltage detected",
1=>"Arm frequency capped",
2=>"Currently throttled",
3=>"Soft temperature limit active",
16=>"Under-voltage has occurred",
17=>"Arm frequency capped has occurred",
18=>"Throttling has occurred",
19=>"Soft temperature limit has occurred");

$output=exec("vcgencmd get_throttled");
$output=explode("0x",$output);

if ($output[1]=="0") {
    echo "all fine, lucky you\n";
    exit();
}

$output=str_split($output[1]);
$bincode="";
foreach ($output as $hex) {
    $bincode.=str_pad(base_convert($hex,16,2),4,"0",STR_PAD_LEFT);
}
$bincode=array_reverse(str_split($bincode));
foreach ($bincode as $k=>$v) {
    if ($v) {
        echo $codes[$k]."\n";
    }
}

And then run:
php throttled.php

Display correct Raspberry CPU frequency in byobu status bar

I love byobu, since when I first discovered it existed me years ago. I didn’t even know screen was a thing back then, but byobu… oh byobu.

So anyway, I’ve come to rely a lot on it, and on its status bar, which with time allowed to display “accurately” both CPU temperature and clock.

On Raspberry Pi, I just discovered, byobu doesn’t always show the correct clock.

I noticed that the command:

vcgencmd measure_clock arm

returned a lower CPU clock, 0.6GHz (and that’s when I finally noticed that my Raspberry Pi 3B+ was permanently throttled because of low voltage).

Delving deeper, I realized that byobu takes the CPU temperature information from something like, if not exactly, this:

sudo cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq

which is the information given back by the Linux Kernel. I’ve read on RaspberryPi’s official forums (couldn’t find the link again now), and the consensus is that kernel is not necessarily correct, but the firmware always is.

The correct CPU clock frequency then must be asked to the firmware with the vcgencmd command above.

Now, how to display the correct clock in byobu status bar?

I used this guide:

http://blog.dustinkirkland.com/2010/01/byobu-custom-status-notifications-in-3.html

and with a litte help from RaspberryPi official forums:

https://www.raspberrypi.org/forums/viewtopic.php?f=91&t=251695

(those guys were REALLY fast in replying)

I created the $HOME/.byobu/bin/5_clk file, containing the following code:

#!/bin/bash
vcgencmd measure_clock arm | awk ' BEGIN { FS="=" } ; { printf("#[fg=#ffffff,bg=cyan]%.1fGHz#[default]\n", $2 / 1000000000) } '

made it executable with

chmod +x $HOME/.byobu/bin/5_clk

and enabled the “custom” row in the byobu toggles, while disabling the native info.

This replaces the cpu frequency info with the same color formatting, and refreshes every 5 seconds.

Control SIM800 with PHP through serial port

…or rather, control anything through serial port with PHP.

This guide will be soon updated to a full-fledged serial console made in PHP (show output from device, but also send commands).

I must say, credit goes to this github repository which in turn is based on another known repository, and which I heavily simplified and stripped down because I don’t like having to deal with PHP classes and everything that has to do with it.

Let’s cut down the overhead, and to the chase.

This is an example code:

function serialread() {
   global $sim800;
   $chars = [];
   do {
     $char = fread($sim800, 1);
     $chars[] = $char;
   } while ($char != "\n" && $char != "");
   return join('', $chars);
}

exec("stty -F $tty cs8 9600 ignbrk -brkint -icrnl -imaxbel -opost -onlcr -isig -icanon -iexten -echo -echoe -echok -echoctl -echoke noflsh -ixon -crtscts");
$sim800=fopen($tty,"w+b");
stream_set_blocking($sim800, false);
fwrite($sim800,"AT\r");
fwrite($sim800,"AT+DDET=1\r");
fwrite($sim800,"AT+CLIP=1\r");
fwrite($sim800,"ATS0=2\r");
fwrite($sim800,"AT+CMGF=1\r");
sleep(1);

while (true) {
   $data = trim(serialread());
   if (strlen($data)>1) {
     echo $data."\n";
   }
   sleep(1);
}

And now let’s do some explaining.

$tty is the string containing the value of the serial device file, in my case I defined it as $tty="/dev/ttyUSB0"; because I prefer using an external adapter and keeping more juicy GPIO pins to myself.

The $sim800=fopen($tty,"w+b"); instruction opens the serial stream as a writeable and readable file, and resets its content to empty, the b in "w+b" forces the connection to be established in binary format.

The stream_set_blocking($sim800, false); instruction allows the fread() command to immediately return a result, even if null, after calling it, instead of waiting for something to be output to the serial console.

The fwrite() instructions are to initialize the SIM800 module as I like it, you may want to search on the official AT commands of the SIM800 to find their meaning. What’s to be learnt here, is that, after you issue a command string, you want to end it with "\r" which is a carriage return, and sends the Enter key to the console; using "\n" which instead is a newline would not work to issue commands.

I use trim() on the serialread() function (which by the way is stolen from the repository linked above) because the SIM800 likes to add a lot of new lines around, and to parse and/or display the serial ouput of the module it’s better if you have a bare string to process.

That’s all folks.

Backup linux & raspbian important files on dropbox, automatically

I just create a repository on GitHub:

https://github.com/ephestione/bazidrop

It’s about a little tool I wrote, that I needed to have small, fresh backups made regularly of my raspberry pi’s operating system, that I could safely upload to the cloud (hence, encrypted).

I already use https://github.com/lzkelley/bkup_rpimage to make regular backups of my systems, but that creates 4GB .img files (even if sparse) that I cannot easily move around, and include all the contents of the sytem, even those files that can be restored with a new installation.

Instead, I needed to systematically backup my home folder, crontabs, apache files, mysql databases (maybe you have something else in mind), zip everything, and put it on dropbox.

This is the reason I wrote bazidrop.sh, which I think someone else could find useful.

Apache on Raspbian using older version of PHP

A few weeks ago I used this tutorial to install PHP 7.3 on my Raspbian.

Fast forward to today, I was bashing my head because after 2 hours of messing around, I could have exec() work from PHP CLI but not from the browser.

php -v from CLI correctly reported 7.3, so what gives?

After two hours I also decided to try phpinfo() from the browser, and guess what, it was still using 7.0!

So, after:

sudo a2dismod php7.0
sudo service apache2 restart

phpinfo() correctly reported 7.3 and I had my exec() working as intended.

Protect empty mountpoint from write access when drive is not mounted in Raspbian and Linux

I knew I had read something to this effect in the past since one of my raspi‘s had this thing where you couldn’t write to a mountpoint unless the drive/USB disk was actually mounted.

Since I spent some time in finding it again, here I add it to my blog as personal reference.

From this post:

Always set the attributes of mountpoint directories to immutable using chattr.

This is accomplished with chattr +i /mountpoint (with the mount unmounted).

This would error-out on new write activity and also protects the mount point in other situations.

lighttpd cannot install because of libssl1.1, how to fix

My situation happened on a Raspberry with Raspbian Stretch installed, I had added PHP7.0 repository from sury.org quite a while back and when by chance today I went to open PiHole admin page from my laptop it simply wouldn’t load.

Google what’s up, I found out lighttpd was maybe the culprit, look around and noticed it wasn’t installed, and couldn’t be installed with the error:

lighttpd : Depends: libssl1.1 (>= 1.1.0) but it is not going to be installed

I then discovered that said libssl1.1 library off sury.org, coming together with the PHP distro, broke lighttpd.

I removed the repository source from /etc/apt/sources.list.d/php.list (your filename may vary) and issued a sudo apt-get update followed by a dist-upgrade but that didn’t solve anything.

I couldn’t find for the life of me a way to simply exchange the libssl1.1 package (which was kept from the sury.org repository even after removing its source) to the original repository version, and

sudo apt-get remove libsll1.1

wanted me to remove also ALL the packages that depended on this library. And they were a LOT.

Like hell I wanted to do that!

Or not?

Well I tried

sudo apt-get install --reinstall libssl1.1

hoping it would get rid of the messy libssl1.1 exchanging it with the official repository one, but that also gave an error:

Reinstallation of libssl1.1 is not possible, it cannot be downloaded.

Sooooo I was getting out of options and very annoyed.

I thought, why not letting the frigging apt remove all those packages? I can always install them later on… I hope…

So I copied the list of the packages that were to be removed off putty window and into notepad++, crossed my fingers and let apt remove everything.

After that was done during an extremely long and suffered delay, I had to do

sudo apt-get install <paste big-ass list of packages here>

In my case, it didn’t work out that simply at the first try, I got some CRC mismatch somewhere so they were not installed all together.

But I issued the command with less packages listed, beginning with apache2 php7.0 mysql-server transmission-cli samba python somethingIcannotreallyrecallnow, and then reissued the first command with all the list again to fill in the blanks.

It installed everything piece by piece, and lighttpd with it as well.

Since apt-get actually removes those packages without purging them (unless you ask it to purge libssl1.1 which isn’t a good idea) their settings are kept and reinstalling the packages will restore the system to the previous state.

At least it did for me, since the system came back to normal after a reboot.

lftp and source: Is a directory error

I was running lftp with the -f switch to launch the usual mirror command, working fine with a few ftp servers at first, but when I added another sync with a pure-ftpd server something stopped working as intended: the message

source: Is a directory

appeared and nothing more happened, only after I pressed Enter the script went on with the execution.

What helped me was this discussion.

so I changed my script, and instead of having

open host
user username password
mirror blahblah

I used

open -u username,password host
mirror blahblah

and everything was magically fine!

Why? NO IDEA. Who cares. Works now.

Change user of transmission-daemon under Debian and Raspbian

UPDATE: Cristian commented adding a nice solution (which I didn’t personally test though, so it’s on you):

  1.  run chmod 775 on the download folder, with -R option (recursive on subfolders):
    sudo chmod -R ug+rw folderName
  2.  add your own user (the one you need to be able to access the downloaded files) to debian-transmission group, or any other group that the transmission daemon belongs to:
    sudo usermod -a -G groupName userName

And that would be all.

Though, after some tinkering that occurred as of june 2019, I found that my original, following, solution has a -probably- nicer “feature” for someone: the config folder of transmission is saved in your own home folder, instead of /var/lib/transmission-daemon/blahblah, in my case this saved some waste of time.

This is the original article with the original solution.

I have a raspi3 running transmission daemon downloading to an external USB drive shared via Samba. I don’t want to keep using debian-transmission user with the daemon since just switching to my user account having the access rights to the external USB is much simpler.

I had it already nice and running before, but updating the daemon with apt-get messed everything (and lost all the running torrents as well) so I had to rediscover the procedure once again, and for posterity (and myself for future occasions) I’m writing it down here.

By the way all the missing torrents appeared again after I solved the issue.

So, here are the things you need to do:

  1. run sudo service transmission-daemon stop just in case
  2. edit /etc/init.d/transmission-daemon to have USER=username
  3. edit /lib/systemd/system/transmission-daemon.service to the same effect
  4. run sudo chown -R user:user /etc/transmission-daemon/
  5. run sudo chown -R user:user /var/lib/transmission-daemon/

Done.

 

According to a comment of this article, this might not work for you, so instead you might want to follow this guide instead:

https://askubuntu.com/questions/261252/how-do-i-change-the-user-transmission-runs-under/544185#544185