Antonello's questions

I have a Ubuntu 20.04 server where ssh X tunnelling has always worked, so that my colleagues can run programs like qgis et co using MobaXTerm on windows or just SSH -XC (the few) on Linux.

The problem now it is no longer working with xclock telling me it can't open the display (and indeed I have nothing on echo $DISPLAY)

If I understood correctly the (old) documentation on ServerGUI, there are two ways to get graphical applications forwarded on SSH:

1. Use xauth on the host (server) and the actual X server on the client
2. Use a full yet minimal xorg + openbox on the server I have tried both approaches but can't get it working. Also I do not understand the advantages of using one or the other (my machine has 128GB of RAM)

I already have set ForwardX11 yes and ForwardX11Trusted yes on /etc/ssh/ssh_config and X11Forwarding yes on /etc/ssh/sshd_config (and played with both yes and no on X11UseLocalhost)

So, what am I missing to get back SSH X tunneling working ? Can be a problem of iptable firewall (but "normal" SSH works - albeit on a non standard 55000 port) ?

EDIT: That seems to be related to having disabled IPV6 on /etc/sysctl.con:

net.ipv6.conf.all.disable_ipv6=1
net.ipv6.conf.default.disable_ipv6=1
net.ipv6.conf.lo.disable_ipv6=1

I do not want however ipv6, somehow my IPS reports very large amount of data with ipv6 on and I haven't put any iptables rules on ipv6.... Is there a way to tell sshd to use ipv4 for tunnelling? I have tried adding AddressFamily inet to /etc/ssh/sshd_config but that doesn't work.

I have a DELL touchscreen convertible and I would like to be able to read, but also annotate with a stylo like I am used on paper, a pdf, so to say bye bye to paper.

I can't find any PDF reader however that fulfil my needs. Ideally the reader would:

• have just a few buttons to manage settings (colour, width, erase..) of the pensil and leave the rest of the area for the pdf content
• once the pencil is selected stay with it (no okular), no need to select it again and again for any "line"
• have a dark mode as Evince
• (optional) keep the file format as an annotated PDF
• have some basic touch gestures like switching page, zoom, exit full screen
• when the pencil is recognised, disable the touch with the hand (if I write on the screen with the pencil, I don't want that the side of my hand makes lots of other sign on the screen)

I have tried Xournal, Scribus, pdfstudioviewer, Okular and a few more, but none is really usable for the task I am looking for. I never had a dedicated book reader, but maybe that is instead the solution to go ? What do you think ?

Even with the Brother own drivers installed, the scan part of "Brother DCP L2550DN" is not working (scan not found, sometimes even scanning but returning an error) on simple-scan or xsane in Ubuntu 20.04, while it was working on earlier versions.

(Note that this is a solved question, posted for others to get the solution quickly)

I wanted to have a look at kubuntu, so I did install the package kde-standard.

I have now removed it and issued a apt autoremove but in ubuntu I am still left with the icons, mouse pointer, windows styles, etc.. of Plasma and the desktop also feels a bit slower.. how can I go back to standard default gnome-based ubuntu?

There are some similar questions here, but they refer to much older versions of Ubuntu and seem to be ubuntu-version specific.

EDIT

• I have tried sudo apt install --reinstall ubuntu-mono but not effect
• top returns me a 99.7% CPU consumption of baloo_file_extr. I understood it is a KDE indexing service. Strange that apt autoremove didn't get rid of it. How can I remove it ?

EDIT 2

• I have tried to reinstall kde-desktop only to then sudo apt autoremove --purge kde-desktop and the same then for dolphin (whay wasn't removed automatically ?)
• After reboot... tada.. stuck with a Bluetooth issue "failed to send firmware data"
• in recovery mode "dpkg repair broken packake" didn't help, so I get the root prompt and issue a apt-cache depends ubuntu-desktop | grep '[ |]Depends: [^<]' | cut -d: -f2 | tr -d ' ' | xargs apt-get --reinstall install -y

Now I got rid of the Bluetooth issue and the choppy system, but incredible I still have the styles/icons of KDE !! I think I'll gonna make install ubuntu back from scratch...

Bottom line, not run apt-get install kde-standard in ubuntu 20.04 !! If you want to try kubuntu, better you do in a different partition or in a VM..

EDIT 3

• I noticed that if I create a new user, he has the standard ubuntu stuff.. how can I "reset" my user to use standard style/icons ?

EDIT 4 (solved)

• just run as local user:
• gsettings reset org.gnome.desktop.interface gtk-theme
• gsettings reset org.gnome.desktop.interface icon-theme

.....ahhhhh...

Which is the simplest way to "isolate" Apache virtual sites, so that a potentially compromised site doesn't affect the other sites or the server?

To be clear, I am not interested much is scalability, portability, etc, just how to insulate a few small sites currently running as Apache virtual hosts in a relatively powerful home-server that does other things as well (file server, media server,...), so docker solutions seems a bit over the top..

I have realized that edubuntu is no longer available for recent Ubuntus, and that the projects has been somehow replaced by ubuntued. Ubuntued seems to provide the following bundle of packages (in form of meta-packages):

• ubuntued-meta-preschool
• ubuntued-meta-primary
• ubuntued-meta-secondary
• ubuntued-meta-tertiary

As ubuntued seems to be based on Ubuntu, I assume to find and install these packages on my Ubuntu 20.04 all I need to do, instead of installing ex-novo ubuntued, is to add their repositories. But which are those?

Alternatively, are there available "just" some curated meta-packages for the "standard" Ubuntu?

Our new printer (Toshiba e_STUDIO 3515) ignores the printing side, printing always on the long side, whatever selected in the printing dialogue.

Fine, but when I print two pages per sheet I prefer having the double printing on the shortest side..

Note also that while printed documents with Evince or Libreoffice have this problem, printing from Okular works fine, respecting the printing side.

Anything I can do to solve this problem ?

This question may look similar to this or this one but the difference here is that the process in question is Firefox, i.e. it is under user space and it is not related to mounting stuff.

In my case the rest of the system was responsive, only Firefox got halted.

What else could stop sudo kill -9 to work and how could I go back to a healthy environment without physical unplugging the power (even reboot didn't work) ?

My integrated camera works but blink/flash (like if I am dancing on a disco..) and displays only B/W images.

This is independent of the application, e.g. on Skype, Cheese, etc.

I'm on a Dell Latitude 5290 with Ubuntu 18.04

sudo lshw:

[...]
description: Detachable
product: Latitude 5290 2-in-1 (081D)
vendor: Dell Inc.
serial: BK4BJR2
width: 64 bits
capabilities: smbios-3.1 dmi-3.1 smp vsyscall32
configuration: boot=normal chassis=docking family=Latitude sku=081D uuid=44454C4C-4B00-1034-8042-C2C04F4A5232
[...]
          *-usb:1
               description: Video
               product: Integrated_Webcam_HD
               vendor: CNFGE16O39442000DBB0
               physical id: 5
               bus info: usb@1:5
               version: 70.05
               serial: 0001
               capabilities: usb-2.01
               configuration: driver=uvcvideo maxpower=500mA speed=480Mbit/s
[...]

Any idea what could I do to make it working ?

Using Ubuntu 18.04 I have some screencast video files in mp4 container (h.264/mp3 codecs) that I want at times merge (i.e. C.mp4 = A.mp4+B.mp4) or at times cut removing some intervals (e.g. D.mp4 = A.mp4[0,320{seconds}]+A.mp4[325,340]+C.mp4).

I am now using kdenlive, it woks but it re-encode everything and it seems a bit too much for such a task.

Is there a simpler way to do that without re-encoding (even, and perhaps preferred, command line or stable Python/Julia/R/.. way) ?

I am thinking at something like PDFtk for the pdfs :-))

PS: I did try ffmpeg -ss 00:00:05 -to 00:00:10 -i test1.mp4 test2.mp4 but I have an error:

Option to (record or transcode stop time) cannot be applied to input url test1.mp4 -- you are trying to apply an input option to an output file or vice versa. Move this option before the file it belongs to.

My files have the same container, codec and resolution.

(I know nothing of video stuff..)

EDIT: I don't want to look pessimistic, but more I look on it more I behave that what I thought to be super simple is indeed super complicate. What a pity nobody wrote a high-level interface to perform something like that.. I'm sure I am not the first one with such a need..

EDIT2: I found moviepy, but it is still far from my original idea (it re-encodes and it has longer than needed API.. I can script it but the reencoding problem remains):

pip install moviepy

from moviepy.editor import VideoFileClip, concatenate_videoclips
c1 = VideoFileClip("test1.mp4").subclip(0,5)
c2 = VideoFileClip("test1.mp4").subclip(10,15)
f = concatenate_videoclips([c1,c2])
f.write_videofile(test2.mp4)

I have an ubuntu server where I installed xauth, xorg and openbox in order to access individual graphical applications from remote using ssh tunelling, e.g.

ssh -XC [email protected] qgis

How can I disable effects like fading menus on the server in order to further improve speed ?

(PS: I am not 100% sure I am running openbox behind the scene)

I'm on my first dedicated server.

When I set up a minimal Ubuntu 16.04 server and ssh on it I find:

root@Ubuntu-1604-xenial-64-minimal ~ # df -lh
Filesystem      Size  Used Avail Use% Mounted on
udev             32G     0   32G   0% /dev
tmpfs           6,3G   13M  6,3G   1% /run
/dev/md2        438G  1,1G  414G   1% /
tmpfs            32G     0   32G   0% /dev/shm
tmpfs           5,0M     0  5,0M   0% /run/lock
tmpfs            32G     0   32G   0% /sys/fs/cgroup
/dev/md1        488M   60M  403M  13% /boot
tmpfs           6,3G     0  6,3G   0% /run/user/0

I normally set /home and / partition separately, but here I had no partition choice.

How do I shrink / to let's say 30 GB and keep the rest to /home ?

EDIT: The hosting company also offers a "rescue" system, a Linux live environment that allows to have administrative access to the server. The environment starts from the network (PXE boot) and runs in the memory of the server. This makes it possible to carry out repairs to the installed system, to check file systems or to install a new operating system.

Should I use this system to shrink the root partition first ?

EDIT 2: The server uses software RAID:

$cat /proc/mdstat
Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5] [raid4] [raid10] 
md0 : active raid1 sdb1[1] sda1[0]
      33521664 blocks super 1.2 [2/2] [UU]

md2 : active raid1 sdb3[1] sda3[0]
      465895744 blocks super 1.2 [2/2] [UU]
      [==================>..]  resync = 94.5% (440301824/465895744) finish=4.2min speed=100467K/sec
      bitmap: 1/4 pages [4KB], 65536KB chunk

md1 : active raid1 sdb2[1] sda2[0]
      523712 blocks super 1.2 [2/2] [UU]

unused devices: <none>

I would like to use my unbranded chinease "air mouse + keyboard", that I normally use at home connected to an android tv, on a Ubuntu 16.04 laptop at work for making presentation annotations.

Basically, I need the air mouse functionality: you move the tool and the mouse position change on the screen.

I did plug the usb receiver on the pc, but nothing happens. How can I debug it to check if a driver for it exists ?

I know you can do the same now with an android tv working as remote, but keeping a phone on hand for 2-3 hours starts to be heavy!

It was months I was noticing my Dell laptop [Ubuntu 16.04] becoming suddenly slower, now I tracked down it happens when I unplug it from its own docking station. It doesn't seems to be related to power socks or no internet, as I have the same problem e.g. when I work from the train with the laptop connected to the sock.. it's just when it is out of its docking station.. See the following console session where I benchmark a dummy function using Julia (the problem is not in Julia.. I have problems also in compiling big pdf from LaTeX on any other computationally-intensive problem). There seems not to be any problem in other processes eating CPU or memory.

$ julia
               _
   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: http://docs.julialang.org
   _ _   _| |_  __ _   |  Type "?help" for help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.5.1 (2017-03-05 13:25 UTC)
 _/ |\__'_|_|_|\__'_|  |  Official http://julialang.org/ release
|__/                   |  x86_64-pc-linux-gnu


julia> function f(n)
       s = 0
       for i = 1:n
       s += i/2
       end
       s
       end
f (generic function with 1 method)

julia> @time f(100000000)
  1.948031 seconds (300.00 M allocations: 4.470 GB, 14.57% gc time)
2.500000025e15

julia> @time f(100000000)
  1.771005 seconds (300.00 M allocations: 4.470 GB, 7.27% gc time)
2.500000025e15

julia> @time f(100000000)
  1.764294 seconds (300.00 M allocations: 4.470 GB, 7.00% gc time)
2.500000025e15

julia> @time f(100000000)
  1.776455 seconds (300.00 M allocations: 4.470 GB, 7.06% gc time)
2.500000025e15

julia> @time f(100000000)
  1.791494 seconds (300.00 M allocations: 4.470 GB, 7.12% gc time)
2.500000025e15

julia> @time f(100000000) # here I unplug the laptop from the docking station
 11.927460 seconds (300.00 M allocations: 4.470 GB, 5.56% gc time)
2.500000025e15

julia> @time f(100000000)
 12.201062 seconds (300.00 M allocations: 4.470 GB, 5.50% gc time)
2.500000025e15

julia> @time f(100000000) # here I plugged the power cord directly to the laptop
 11.839180 seconds (300.00 M allocations: 4.470 GB, 5.62% gc time)
2.500000025e15

julia> @time f(100000000) # here I removed internet conection, including wifi
 11.860953 seconds (300.00 M allocations: 4.470 GB, 5.65% gc time)
2.500000025e15

julia> @time f(100000000) # here I plugged back the laptop on the deck
 11.789184 seconds (300.00 M allocations: 4.470 GB, 5.63% gc time)
2.500000025e15

julia> @time f(100000000) # here I switched the keyboqrd to English lqnguqge
 11.857721 seconds (300.00 M allocations: 4.470 GB, 5.68% gc time)
2.500000025e15

julia> @time f(100000000) # here I closed the screen of the laptop and worked back on the main screen
 12.001792 seconds (300.00 M allocations: 4.470 GB, 5.63% gc time)
2.500000025e15

julia> @time f(100000000) # here I am back to ethernet
 11.865361 seconds (300.00 M allocations: 4.470 GB, 5.71% gc time)
2.500000025e15

julia> exit()
$ julia
               _
   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: http://docs.julialang.org
   _ _   _| |_  __ _   |  Type "?help" for help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.5.1 (2017-03-05 13:25 UTC)
 _/ |\__'_|_|_|\__'_|  |  Official http://julialang.org/ release
|__/                   |  x86_64-pc-linux-gnu

julia> @time f(100000000) # here I went off and on Julia
ERROR: UndefVarError: f not defined

julia> function f(n)
              s = 0
              for i = 1:n
              s += i/2
              end
              s
              end
f (generic function with 1 method)

julia> @time f(100000000) # here I went off and on Julia
 12.809319 seconds (300.00 M allocations: 4.470 GB, 11.16% gc time)
2.500000025e15

julia> @time f(100000000) # here after lot of time (lunch break)
 11.916337 seconds (300.00 M allocations: 4.470 GB, 5.49% gc time)
2.500000025e15

julia> quit()
$ julia
               _
   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: http://docs.julialang.org
   _ _   _| |_  __ _   |  Type "?help" for help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.5.1 (2017-03-05 13:25 UTC)
 _/ |\__'_|_|_|\__'_|  |  Official http://julialang.org/ release
|__/                   |  x86_64-pc-linux-gnu

julia> @time f(100000000) # here after suspended the pc and julia stop/restart
ERROR: UndefVarError: f not defined

julia> function f(n)
              s = 0
              for i = 1:n
              s += i/2
              end
              s
              end
f (generic function with 1 method)

julia> @time f(100000000) # here after suspended the pc and julia stop/restart
  1.952593 seconds (300.00 M allocations: 4.470 GB, 14.26% gc time)
2.500000025e15

julia> @time f(100000000) # here after suspended the pc and julia stop/restart
  1.824997 seconds (300.00 M allocations: 4.470 GB, 6.34% gc time)
2.500000025e15

julia> 

EDITED: The following transcript show something interesting.. in the previous unplug from the docking station I did it with the screen closed, now I unplug it with the screen on and in this way it works.. until I do remove the power plug and do a suspend/resume.. then it does not work, then I plug the power, do a suspend/resume and it works well again... It seems it goes in low-consumption mode and it doesn't matter if you plug back the power, you need to also give the laptop a suspend/resume in order for the laptop to realise it is plugged back...

 quit()
lobianco@lobianco-officeLinux:~/Dropbox/Documenti/Varie/lef/papers/ffsm++/versions/07_carbon_balance_with_multipliers$ julia
               _
   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: http://docs.julialang.org
   _ _   _| |_  __ _   |  Type "?help" for help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.5.1 (2017-03-05 13:25 UTC)
 _/ |\__'_|_|_|\__'_|  |  Official http://julialang.org/ release
|__/                   |  x86_64-pc-linux-gnu

julia> function f(n)
              s = 0
              for i = 1:n
              s += i/2
              end
              s
              end
f (generic function with 1 method)

julia> @time f(100000000) # after switched off internet and moved back to french
  1.939228 seconds (300.00 M allocations: 4.470 GB, 13.96% gc time)
2.500000025e15

julia> @time f(100000000) # after switched off internet and moved back to french
  1.761612 seconds (300.00 M allocations: 4.470 GB, 6.42% gc time)
2.500000025e15

julia> @time f(100000000) # after unplugged power but still laptop on his own deck
  1.775432 seconds (300.00 M allocations: 4.470 GB, 6.30% gc time)
2.500000025e15

julia> @time f(100000000) # after removing laptop from the deck (still unplugged)
  1.770068 seconds (300.00 M allocations: 4.470 GB, 6.28% gc time)
2.500000025e15

julia> @time f(100000000) # after removing laptop from the deck (still unplugged)
  1.744716 seconds (300.00 M allocations: 4.470 GB, 6.32% gc time)
2.500000025e15

julia> @time f(100000000) # after suspend/resume
 11.743261 seconds (300.00 M allocations: 4.470 GB, 5.28% gc time)
2.500000025e15

julia> @time f(100000000) # after plugging the power (still disconnected from deck)
 11.722175 seconds (300.00 M allocations: 4.470 GB, 5.30% gc time)
2.500000025e15

julia> @time f(100000000) # after suspend/resume
  1.770605 seconds (300.00 M allocations: 4.470 GB, 6.29% gc time)
2.500000025e15

julia> 

I recently installed Ubuntu 16.04 (fresh installation), but I have lot of problems with LibreOffice. I am not more specific, as these problems seems of various nature, with windows not updating, crashing and so on. I had no problems in 14.04.

So, I would like to "reset" LibreOffice and reinstall it. What is the best way to reinstall all the LibreOffice packages in Ubuntu 16.04?

UPDATED: I did lookup for all LibreOffice packages in Synaptic and "purged" them before reinstalling, but I still have problems as you can see from the following screenshot (editing math formula is not the only problem, but it is the most repeatable one, so I am using it as a benchmark of things working or not)

after installing several packages with the package manager, some others using eggs, some others using pip, for 2 versions of python, with some packages that in the meantime changed name (iPython --> Jupyter).. briefly, my python installation is in a mess state!

How can I reset both system and local python systems to default ubuntu 14.04 ?

I have a Ubuntu 14.04 VPS with a few sites.

If I run php -r "mail('[email protected], 'test', 'test');" this gets delivered, but I have a couple of CMSs (Drupal and dokuwiki) that don't send any emails, including basic password reminder/registration.

I have checked and I am not blacklisted. Where should I look to start debugging ?

Edit: it seems the problem is that I have the incoming emails using a third party while postfix try to deliver the email locally (maybe looking at the alias file?).

How can I force postfix to NOT try to deliver the email locally ?

[Solved]

Ubuntu 12.10 x64 new i7 laptop, mysql default installation.

Importing a 6 MB dump file (a empty drupal dump made mostly of INSERT INTO statements) takes ~30 minutes, on other PC takes less than a minute.

I created an ext3 partition and monted /var/lib/mysql there, but it didn't solve the problem.

iostat -x :

Linux 3.5.0-27-generic (lobiancoOfficeLinux)    09/04/2013  _x86_64_    (8 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           2,44    0,01    0,49    2,44    0,00   94,62

Device:         rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s avgrq-sz avgqu-sz   await r_await w_await  svctm  %util
sda              34,47    68,87    9,86   31,42   388,97   420,90    39,24     1,51   36,56   37,10   36,39   9,65  39,85

What else could it be to give mysql such a slow performance ?

I don't know if it's related, but also opening the dump.sql file with gedit or kate is pretty slow..

I need to shrink an ext4 /home partition (/dev/sda9) to make space for something else.

I would prefer avoid live CDs (boot troubles with new EFI and. I don't have a CD/USB in hand in the office).

I can boot as root directly to command line so I can unmount /home but then, for some reasons, I can't use the GUI even for the root user, so I can't use GParted.

Is there a terminal command to resize an unmounted ext4 partition without losing data ?

LibreOffice in the latest version of Ubuntu (12.10) is pretty bugged, with several open bugs on things like menus and windows.

How to get a version, even ugly but working, of libreoffice without any unity integration ?