pa4080's questions

Background of the question: I'm playing with Pop!_OS in a virtual machine and trying to setup the audio for the xRDP service. At this moment it looks like it is not possible because they've switched to PipeWire and for some reason its PulseAudio wrapper is not fully compatible with the package xrdp-pulseaudio-installer... nor with the building process mentioned below.

In addition on Ubuntu 18.04 I was using the package xrdp-pulseaudio-installer which for some reason is not available on Ubuntu 19.04+ (nor the package pulseaudio-module-xrdp which is available on Kali). So we need to build it manually as it is described in this topic.

The question: Initially I was thinking PipeWire is a newer audio service and it has a PulseAudio wrapper for backward compatibility. But I found on my Ubuntu 22.04 both services are enabled and running. Or at least both commands below report active (running).

systemctl --user status pulseaudio.service
systemctl --user status pipewire.service

So my questions are:

• What is the relation between PipeWire and PulseAudio on Ubuntu 22.04?
• How to determinate which of them actually provides the audio on my system?

Is there a way to force the sudo command to ask for a password each time when I'm using sudo rm /path/file?

I want to protect my self from stupid mistakes, committed due to low attention when I'm running some commands from the history.

I'm looking for a way to move the application menu in the window's title bar on the left side as it is illustrated on the next image.

Optionally, I will be happy if there is some way to force such application menu to appear for non-GTK windows as Firefox, Chromium, GIMP, etc.

My VPS wasn't rebooted for about 3 months. It is hosted on a server with OpenVZ virtualization type and the operating system is Ubuntu 16.04. For some reason, I rebooted the VPS and after that, I couldn't connect to the server through ssh, the message that I received is:

ssh: connect to host srvname.com port 22: Connection refused

So I opened a Serial Console on the VPS and start investigating... I've purged and reinstalled the openssh-server with no success. I spent two hours reading articles, question, and answers about similar issues on Internet.

Finally I managed to understand that the directory /var/run/sshd is not created during the system startup. And once I create it manually I can start the SSH service without any problem, but on the next reboot the issue remains. So my questions are:

• What could be the cause of this issue? Why /var/run/sshd is not created during the system startup?

• How can I solve the issue in a proper way? I found a temporal solution that is mentioned at the end of this post.

• Does the issue could be related to the OpenVZ host of the VPS? Should I ask the hosting provider to solve it?

The output of systemctl status ssh.service, sshd -Ddp 22 and journalctl -xe is:

# systemctl status ssh.service
● ssh.service - OpenBSD Secure Shell server
   Loaded: loaded (/lib/systemd/system/ssh.service; enabled; vendor preset: enabled)
   Active: failed (Result: start-limit-hit) since вт 2019-01-15 12:58:08 EET; 22s ago
  Process: 407 ExecStartPre=/usr/sbin/sshd -t (code=exited, status=255)

яну 15 12:58:07 srvname systemd[1]: Failed to start OpenBSD Secure Shell server.
яну 15 12:58:07 srvname systemd[1]: ssh.service: Unit entered failed state.
яну 15 12:58:07 srvname systemd[1]: ssh.service: Failed with result 'exit-code'.
яну 15 12:58:08 srvname systemd[1]: ssh.service: Service hold-off time over, scheduling restart.
яну 15 12:58:08 srvname systemd[1]: Stopped OpenBSD Secure Shell server.
яну 15 12:58:08 srvname systemd[1]: ssh.service: Start request repeated too quickly.
яну 15 12:58:08 srvname systemd[1]: Failed to start OpenBSD Secure Shell server.
яну 15 12:58:08 srvname systemd[1]: ssh.service: Unit entered failed state.
яну 15 12:58:08 srvname systemd[1]: ssh.service: Failed with result 'start-limit-hit'.


# $(which sshd) -Ddp 22
debug1: sshd version OpenSSH_7.2, OpenSSL 1.0.2g  1 Mar 2016
debug1: private host key #0: ssh-rsa SHA256:...
debug1: private host key #1: ssh-dss SHA256:...
debug1: private host key #2: ecdsa-sha2-nistp256 SHA256:...
debug1: private host key #3: ssh-ed25519 SHA256:...
Missing privilege separation directory: /var/run/sshd


# journalctl -xe
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit ssh.service has begun starting up.
яну 15 13:21:21 srvname sshd[1688]: Missing privilege separation directory: /var/run/sshd
яну 15 13:21:21 srvname systemd[1]: ssh.service: Control process exited, code=exited status=255
яну 15 13:21:21 srvname systemd[1]: Failed to start OpenBSD Secure Shell server.
-- Subject: Unit ssh.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit ssh.service has failed.
-- 
-- The result is failed.
яну 15 13:21:21 srvname systemd[1]: ssh.service: Unit entered failed state.
яну 15 13:21:21 srvname systemd[1]: ssh.service: Failed with result 'exit-code'.
яну 15 13:21:22 srvname systemd[1]: ssh.service: Service hold-off time over, scheduling restart.
яну 15 13:21:22 srvname systemd[1]: Stopped OpenBSD Secure Shell server.
-- Subject: Unit ssh.service has finished shutting down
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit ssh.service has finished shutting down.
яну 15 13:21:22 srvname systemd[1]: Starting OpenBSD Secure Shell server...
-- Subject: Unit ssh.service has begun start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit ssh.service has begun starting up.
яну 15 13:21:22 srvname sshd[1691]: Missing privilege separation directory: /var/run/sshd
яну 15 13:21:22 srvname systemd[1]: ssh.service: Control process exited, code=exited status=255
яну 15 13:21:22 srvname systemd[1]: Failed to start OpenBSD Secure Shell server.
-- Subject: Unit ssh.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit ssh.service has failed.
-- 
-- The result is failed.
яну 15 13:21:22 srvname systemd[1]: ssh.service: Unit entered failed state.
яну 15 13:21:22 srvname systemd[1]: ssh.service: Failed with result 'exit-code'.
яну 15 13:21:22 srvname systemd[1]: ssh.service: Service hold-off time over, scheduling restart.
яну 15 13:21:22 srvname systemd[1]: Stopped OpenBSD Secure Shell server.
-- Subject: Unit ssh.service has finished shutting down
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit ssh.service has finished shutting down.
яну 15 13:21:22 srvname systemd[1]: ssh.service: Start request repeated too quickly.
яну 15 13:21:22 srvname systemd[1]: Failed to start OpenBSD Secure Shell server.
-- Subject: Unit ssh.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit ssh.service has failed.
-- 
-- The result is failed.
яну 15 13:21:22 srvname systemd[1]: ssh.service: Unit entered failed state.
яну 15 13:21:22 srvname systemd[1]: ssh.service: Failed with result 'start-limit-hit'.

The content of /usr/lib/tmpfiles.d/sshd.conf and /etc/init/ssh.conf is:

# cat /usr/lib/tmpfiles.d/sshd.conf 
d /var/run/sshd 0755 root root

# cat /etc/init/ssh.conf | sed '/^#/ d'

description "OpenSSH server"

start on runlevel [2345]
stop on runlevel [!2345]

respawn
respawn limit 10 5
umask 022

env SSH_SIGSTOP=1
expect stop

console none

pre-start script
    test -x /usr/sbin/sshd || { stop; exit 0; }
    test -e /etc/ssh/sshd_not_to_be_run && { stop; exit 0; }

    mkdir -p -m0755 /var/run/sshd
end script

exec /usr/sbin/sshd -D

Additional information about the system:

# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 16.04.5 LTS
Release:    16.04
Codename:   xenial

# uname -a
Linux srvname 2.6.32-042stab127.2 #1 SMP Thu Jan 4 16:41:44 MSK 2018 x86_64 x86_64 x86_64 GNU/Linux

# apt show openssh-server | grep 'Version'
Version: 1:7.2p2-4ubuntu2.6

The temporal solution: I found that /var/run is a symbolic link to /run, I do not know why this is needed, but when I modified the content of the file /usr/lib/tmpfiles.d/sshd.conf from:

d /var/run/sshd 0755 root root

to:

d /run/sshd 0755 root root

everything goes well on system startup, the SSH service is started normally and I'm able to log-in via SSH.

I'm working on a Bash script and the length of the string contained in a certain variable is one of my conditions. The current string is W5u7TBTzF17GGFV8DBJHvgAAAAI. Initially I've count the string length by the help of wc -c:

$ VAR='W5u7TBTzF17GGFV8DBJHvgAAAAI'; echo "$VAR" | wc -c
28

But my script condition [[ ${#VAR} -eq 28 ]] never pass. Then I decided to count the characters on by one. Indeed the string length is 27 characters, also the value of ${#VAR} is 27:

$ echo "${#VAR}"
27

So I'm in wondering - where does this difference come from?

What I want is to find the name of the user that runs bash script, when this script is executed by sudo. The only possible way, that I know, is to parse the output of who -m (who am i) in this way:

user@UbuntuServer:~$ cat who.sh 
#!/bin/sh
whoami
echo $USER
who -m | awk '{print $1}'

user@UbuntuServer:~$ sudo ./who.sh 
root
root
user

The problem is: In Ubuntu Desktop 16.04.4 who -m (resp. who am i) do nothing. Why?

Another question is why the Ubuntu's online manual page for who is different from man who executed either on Ubuntu Desktop or Server?

But these questions are not so important according to my goals. And as it is mentioned in the title, the main question is: How do I find which user executes the script when is used sudo?

Practically, the original title - How do I find 'who am I' on Ubuntu Desktop? - is the same but wrongly asked question.

I'm trying to switch between the audio outputs of my video card from the command line. I'm able to do that via the GUI settings, as it's shown on the picture. How can I do this programmatically?

On the picture are presented two audio devices wit two outputs each:

• (green) Device 1 - Built-in Audio with two outputs:

  • Digital Output
  • Headphones

• (red)      Device 2 - HDMI Audio Controller of NVidia GTX 660. To the video card are connected two monitors:

  • The first monitor is LG TV and it is connected to HDMI-0.

  • The second monitor is LG ULTRAWIDE and it is connected to DVI-I-1.

So I want to switch, via the command-line, between the red outputs (the two monitors). Everything I've found, in my research, is how to switch between the audio devices (sound cards). I've already read few topics as these questions:

• Audio output device, fast switch?
• How to change pulseaudio sink with "pacmd set-default-sink" during playback?
• How can I choose the audio output device using the terminal?
• How to switch sound output with key shortcut

When the first monitor LG TV | HDMI-0 is engaged as audio output:

$ pactl list sinks short
8   alsa_output.pci-0000_00_1b.0.analog-stereo  module-alsa-card.c  s16le 2ch 44100Hz   SUSPENDED
16  alsa_output.pci-0000_03_00.1.hdmi-stereo    module-alsa-card.c  s16le 2ch 44100Hz   RUNNING

$ pacmd list-sinks | grep name:
    name: <alsa_output.pci-0000_00_1b.0.analog-stereo>
    name: <alsa_output.pci-0000_03_00.1.hdmi-stereo>

• output of pactl list sinks
• output of pacmd list-sinks

When the second monitor LG ULTRAWIDE | DVI-I-1 is engaged as audio output:

$ pactl list sinks short
8   alsa_output.pci-0000_00_1b.0.analog-stereo  module-alsa-card.c  s16le 2ch 44100Hz   SUSPENDED
17  alsa_output.pci-0000_03_00.1.hdmi-stereo-extra1 module-alsa-card.c  s16le 2ch 44100Hz   RUNNING

$ pacmd list-sinks | grep name:
    name: <alsa_output.pci-0000_00_1b.0.analog-stereo>
    name: <alsa_output.pci-0000_03_00.1.hdmi-stereo-extra1>

• output of pactl list sinks
• output of pacmd list-sinks

The output of pacmd list-cards and pactl list cards is provided here.

You can see (in this particular case) I'm searching for a way to switch between sink 16 and sink 17. But when sink 16 is presented in pactl list sinks, sink 17 is not presented and vice versa. I can switch them only from the GUI settings. Is ithere a way to do that via the command-line?

I want to find my articles within the deprecated (obsolete) literature forum e-bane.net. Some of the forum modules are disabled, and I can't get a list of articles by their author. Also the site is not indexed by the search engines as Google, Yndex, etc.

The only way to find all of my articles is to open the archive page of the site (fig.1). Then I must select certain year and month - e.g. January 2013 (fig.1). And then I must inspect each article (fig.2) whether in the beginning is written my nickname - pa4080 (fig.3). But there are few thousand articles.

I've read few topics as follow, but none of the solutions fits to my needs:

• Web spider for Ubuntu
• How to write a Web spider on Linux system
• Get a list of URLs from a site

I will post my own solution. But for me is interesting: Is there any more elegant way to solve this task?

I have Lenovo ThinkPad X230 Tablet with Ubuntu 16.04. It has a convertible screen and when it is in tablet mode the touchpad is still active and make a mess.

I've created the following script and bound it to one of the built in buttons (by a custom shortcut):

#!/bin/bash -e

# Find the TouchPad device ID
ID="$(xinput | grep -ioP 'touchpad.*id=\K[0-9]*')"                                  

if   [ "$(LANG=C xinput --list-props "$ID" | awk 'NR==2{print $4}')" == "0" ]; then 
        # If the device is disabled, then enable it and kill 'onboard' virtual keyboard
        xinput enable "$ID"; killall onboard; xrandr -o normal
elif [ "$(LANG=C xinput --list-props "$ID" | awk 'NR==2{print $4}')" == "1" ]; then
        # If the device is enabled, then disable it and run 'onboard' virtual keyboard
        xinput disable "$ID"; nohup onboard >/dev/null 2>&1 &
fi

The script works properly, but this is a fake solution and yesterday I spent few hours to learn how to do that in a proper way. So I decided to share this experience here.

I'm trying to get the content of any /proc/*PID*/environ file in more readable format. I'm able to do that in the way shown below, but I'm sure this isn't the proper way.

$ cat "/proc/$(pgrep gnome-session -n -U $UID)/environ"
USER=spasTEXTDOMAIN=im-configXDG_SEAT=seat0XDG_SESSION_TYPE=waylandSHLVL=1QT4_IM_MODULE=ximHOME=/home/spasDESKTOP_SESSION=ubuntuGNOME_SHELL_SESSION_MODE=ubuntuDBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/busIM_CONFIG_PHASE=2LOGNAME=spasGTK_IM_MODULE=ibusJOURNAL_STREAM=9:147845_=/usr/bin/gnome-sessionUSERNAME=spasXDG_SESSION_ID=70PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/binXDG_RUNTIME_DIR=/run/user/1000LANG=en_US.UTF-8XDG_CURRENT_DESKTOP=ubuntu:GNOMEXDG_SESSION_DESKTOP=ubuntuXMODIFIERS=@im=ibusSHELL=/bin/bashGDMSESSION=ubuntuTEXTDOMAINDIR=/usr/share/locale/XDG_VTNR=2QT_IM_MODULE=ximPWD=/home/spasCLUTTER_IM_MODULE=ximXDG_DATA_DIRS=/usr/share/ubuntu:/usr/local/share:/usr/share:/var/lib/snapd/desktopXDG_CONFIG_DIRS=/etc/xdg/xdg-ubuntu:/etc/xdg

$ cat -e "/proc/$(pgrep gnome-session -n -U $UID)/environ"
USER=spas^@TEXTDOMAIN=im-config^@XDG_SEAT=seat0^@XDG_SESSION_TYPE=wayland^@SHLVL=1^@QT4_IM_MODULE=xim^@HOME=/home/spas^@DESKTOP_SESSION=ubuntu^@GNOME_SHELL_SESSION_MODE=ubuntu^@DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus^@IM_CONFIG_PHASE=2^@LOGNAME=spas^@GTK_IM_MODULE=ibus^@JOURNAL_STREAM=9:147845^@_=/usr/bin/gnome-session^@USERNAME=spas^@XDG_SESSION_ID=70^@PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin^@XDG_RUNTIME_DIR=/run/user/1000^@LANG=en_US.UTF-8^@XDG_CURRENT_DESKTOP=ubuntu:GNOME^@XDG_SESSION_DESKTOP=ubuntu^@XMODIFIERS=@im=ibus^@SHELL=/bin/bash^@GDMSESSION=ubuntu^@TEXTDOMAINDIR=/usr/share/locale/^@XDG_VTNR=2^@QT_IM_MODULE=xim^@PWD=/home/spas^@CLUTTER_IM_MODULE=xim^@XDG_DATA_DIRS=/usr/share/ubuntu:/usr/local/share:/usr/share:/var/lib/snapd/desktop^@XDG_CONFIG_DIRS=/etc/xdg/xdg-ubuntu:/etc/xdg^@

$ cat -e "/proc/$(pgrep gnome-session -n -U $UID)/environ" | sed 's/\^@/\n/g'
USER=spas
TEXTDOMAIN=im-config
XDG_SEAT=seat0
XDG_SESSION_TYPE=wayland
...

Maybe I must assign a specific value to $IFS, but what is it? What is the proper way to achieve the above result?

Recently I've installed Ubuntu 16.04 on Lenovo ThinkPad X230 Tablet. It works just great! I'm experiencing only two minor problems, both are wired with the convertible screen. This one, that annoys me is the subject of this question.

When I login to Unity the display orientation goes to portrait view mode. So, I must press the screen rotation button to get back to landscape view mode.

The default view within LightDM is landscape. The problem doesn't exist when I unlock Unity, only when I log into. This problem doesn't exist when I login to Gnome. But primary I'm using Unity, so my question is: How do I force Unity to stay in landscape view mode immediately after logging into?

Update 1:

• I found that the problem doesn't exist for guest-session and for newly created users.

• It looks like some application rotates the display.

• I already have tried, without success, some solutions based on the answers of these questions:

  • How do I rotate my display when not using an X Server?

  • Screen randomly rotates on Ubuntu 17.10

• Only xrandr -o normal placed as command within Startup Applications is a kind of ugly workaround.

Update 2:

• The original title: How do I force Unity to stay in landscape view immediately after logging into?

Often when I'm editing some system file first I create a backup copy. For example:

sudo cp /etc/ssh/sshd_config /etc/ssh/sshd_config.bak

Is there any simple 'shortcut' such as:

sudo cp /etc/ssh/sshd_config %s.bak

?

A workaround that I found is to use sed in this way:

sudo sed '' /etc/ssh/sshd_config -i.bak

When grep or sed are used with the option --extended-regexp and the pattern {1,9999} is a part of the regexp that is used, the performance of these commands become low. To be more clear, below are applied few tests.^{[1] [2]}

• The relative performance of grep -E, egrep and sed -E is almost equal, so only the test that were made with grep -E are provided.

Test 1

$ time grep -E '[0-9]{1,99}' < /dev/null

real    0m0.002s

Test 2

$ time grep -E '[0-9]{1,9999}' < /dev/null

> real    0m0.494s

Test 3

$ time grep -E '[0123456789]{1,9999}' < /dev/null

> real    21m43.947s

Test 4

$ time grep -E '[0123456789]+' < /dev/null
$ time grep -E '[0123456789]*' < /dev/null
$ time grep -E '[0123456789]{1,}' < /dev/null
$ time grep -P '[0123456789]{1,9999}' < /dev/null

real    0m0.002s       

What is the reason of this significant difference of the performance?

Let's assume we have a computer with Ubuntu Desktop installed on it. There are a few desktop environments (DE) installed such as: Unity, Gnome, KDE, XFCE, Mate, etc.

Also few users have their accounts and they regularly using the computer. Each user could change its DE according to its free will :)

How to determinate which is the current user's desktop environment, for certain user, through CLI within limited environment?

This question could be fragmented in this way:

• In which file is stored this information?

• What is the best way to read it through a script executed within an limited environment such as ssh session or cron?

• How to read this information for random user?

• I'm finding for one line command solution if it is possible.

I have a script that uses at command. And sometimes I receiving emails as this one:

Date: Mon,  3 Jul 2017 14:18:00 +0300 (EEST)
From: root <[email protected]>
To: [email protected]
Subject: Output from your job      173

Another app is currently holding the xtables lock. Perhaps you want to use the -w option?

Of course I would use this option to prevent messages like this, but first I want to know what is the meaning of this option. Unfortunately -w option is not listed in man at.

Does anyone know what exactly this option means?

I wonder - why, when some folder has read or read-write permissions for GROUP (or other), the members of the GROUP (or other) can't access this folder?

I'm almost sure there is a logical explanation, but I can't find it. Let me give an example.

Initial circumstances

1. There are two users, called admin and guest.

2. There is a folder, called /var/www/test-dir:

$ getfacl -pt /var/www/test-dir/
# file: /var/www/test-dir/
USER   root      rwx
GROUP  admin     r-x
other            r-x

3. Within these permissions all users are able to access the folder:

• USER root rwx (7) is able to access the folder.

• GROUP admin r-x (5) is able to access the folder.

• other guest r-x (5) is able to access the folder.

  guest@host:~$ cd /var/www/test-dir/
  guest@host:/var/www/test-dir$ ࢒
  

Cases

Case 1: other has r-- permissions but admin can't access the folder:

root@host:~# chmod 574 /var/www/test-dir/

• USER root r-x (5) is able to access the folder.

• GROUP admin rwx (7) is able to access the folder.

• other guest r-- (4) is unable to access the folder.

  guest@host:~$ cd /var/www/test-dir
  bash: cd: /var/www/test-dir/: Permission denied
  

Case 2: other has rw- permissions but guest can't access the folder:

root@host:~# chmod 656 /var/www/test-dir/

• USER root rw- (6) is able to access the folder.

• GROUP admin r-x (5) is able to access the folder.

• other guest rw- (6) is unable to access the folder:

Case 3: GROUP has r-- permissions but admin can't access the folder:

root@host:~# chmod 745 /var/www/test-dir/

• USER root rwx (7) is able to access the folder.

• GROUP admin r-- (4) is unable to access the folder.

• other guest r-x (5) is able to access the folder.

Case 4: GROUP has rw- permissions but admin can't access the folder:

root@host:~# chmod 467 /var/www/test-dir/

• USER root r-- (4) is able to access the folder.

• GROUP admin rw- (6) is unable to access the folder.

• other guest rwx (7) is able to access the folder.

In other words I want to see how the server looks outside when I don't have access to another machine to scan it. Let me give an example:

Case 1: When I am SSH connected to my VPS, which is Ubuntu Server, the result of port scanning looks like:

[email protected]:~$ nmap -p 1-20000 77.77.77.70

Nmap scan report for 77.77.77.70

PORT      STATE SERVICE
25/tcp    open  smtp
80/tcp    open  http
111/tcp   open  rpcbind
443/tcp   open  https
8142/tcp  open  unknown
11273/tcp open  unknown
18142/tcp open  unknown
18143/tcp open  unknown
18144/tcp open  unknown
18145/tcp open  unknown
18146/tcp open  unknown
18147/tcp open  unknown

Nmap done: 1 IP address (1 host up) scanned in 0.36 seconds

Case 2: When I perform the same command from my Ubuntu Desktop machine the result is filtered by the VPS’s firewall and it looks like:

user@Desktop:~$ sudo nmap -p 1-20000 77.77.77.70

Nmap scan report for 77.77.77.70

PORT      STATE SERVICE
80/tcp    open  http
443/tcp   open  https
11273/tcp open  unknown

Nmap done: 1 IP address (1 host up) scanned in 4298.23 seconds

So, my question is: Is there a way to achieve a result as in 'Case 2' from the VPS itself? Using of nmap is not mandatory.