This is a self-answered question. I've already written an answer but, if you have a better one, please post it.

I'm developing a program and it's printing some time results:

$ homa.py
Creating instance rd = NetworkInfo(): 0.0071680546
Creating instance rd = NetworkInfo(): 0.0083100796
Creating instance rd = NetworkInfo(): 0.0121581554
Creating instance rd = NetworkInfo(): 0.0205171108
Creating instance rd = NetworkInfo(): 0.0067570210
Creating instance rd = NetworkInfo(): 0.0215399265
Creating instance rd = NetworkInfo(): 0.0170729160
Creating instance rd = NetworkInfo(): 0.0088560581
Creating instance rd = NetworkInfo(): 0.0079369545
Creating instance rd = NetworkInfo(): 0.0091099739
Creating instance rd = NetworkInfo(): 0.0085971355
Creating instance rd = NetworkInfo(): 0.0137989521
Creating instance rd = NetworkInfo(): 0.0081419945
Creating instance rd = NetworkInfo(): 0.0090279579
Creating instance rd = NetworkInfo(): 0.0070800781
Creating instance rd = NetworkInfo(): 0.0079300404
^C
homa.py refresh() closed by SIGTERM

It's too difficult to glance at the list and get an average time.

How can I quickly get the average time?

I'm trying to understand how the environment variable _ can be used. Below is an example of using it:

$ echo $_

$ echo $_
echo

$ ls non-existant-filename
ls: cannot access 'non-existant-filename': No such file or directory

$ echo $_
non-existant-filename

• First it returns nothing
• Second it returns the last command used
• Last it returns the last parameter used

This might be a handy variable for bash scripts but only if it's function is fully understood.

Some useful applications of _

I found some useful applications of _.

_ contains the last filename you can recycle

In this example _ is used to keep the last filename which you can reuse in subsequent commands without retying it.

$ ll ~/python/scroll1.py
-rwxrwxrwx 1 rick rick 2384 Dec 27 09:15 /home/rick/python/scroll1.py*

$ $_
# The python program ~/python/scroll1.py is executed

$ cat $_
#!/usr/bin/env python
# -*- coding: utf-8 -*-
   (... SNIP ... remaining contents of ~/python/scroll1.py appears on screen)

• First command uses ll to list a python script filename. The filename is saved to _ for future use.
• Second command $_ runs the python script.
• Third command cat $_ lists the contents of the python script.

So the $_ variable/parameter can save some typing.

_ contains the last program run

Here's an example of differences between env and printenv updating the _ variable/parameter:

$ env > env.txt

$ printenv > printenv.txt

$ diff env.txt printenv.txt
66c66
< _=/usr/bin/env
---
> _=/usr/bin/printenv

Because a parameter wasn't passed to either command, the _ isn't updated with the last used parameter as in the previous example but, it is updated with the last command used.

Also noticed how _ is updated before the commands env and printenv are executed because _ it appears in the output.

I have this code that works:

# Hide irrelevant errors so chrome doesn't email us in cron
if [[ $fCron == true ]] ; then
    google-chrome --headless --disable-gpu --dump-dom \
        "$RobWebAddress" > "$DownloadName" 2>/dev/null
else
    # Get silly error messages when running from terminal
    google-chrome --headless --disable-gpu --dump-dom \
        "$RobWebAddress" > "$DownloadName"
fi

If I try to shorten it like this:

# Hide irrelevant errors so chrome doesn't email us in cron
local HideErrors
[[ $fCron == true ]] && HideErrors="2>/dev/null"

google-chrome --headless --disable-gpu --dump-dom \
    "$RobWebAddress" > "$DownloadName" "$HideErrors"

I get error messages:

[0826/043058.634775:ERROR:headless_shell.cc(597)] Open multiple tabs is only supported when remote debugging is enabled.
[0826/043058.672587:ERROR:headless_shell.cc(597)] Open multiple tabs is only supported when remote debugging is enabled.
[0826/043058.711640:ERROR:headless_shell.cc(597)] Open multiple tabs is only supported when remote debugging is enabled.
(... SNIP ...)

Why does a hard-coded argument work but not an argument as a variable?

Edit 2:

Currently I found success with second answer's alternate suggestion:

# Redirect errors when cron is used to /dev/null to reduce emails
ErrorPipe=/dev/stderr
[[ $fCron == true ]] && ErrorPipe=/dev/null

google-chrome --headless --disable-gpu --dump-dom \
                "$RobWebAddress" > "$DownloadName" 2>"$ErrorPipe"

Edit 1:

Based on the first answer, I should point out program header already contains:

[[ $fCron != true ]] &&
    exec 2> >(grep -v 'GtkDialog mapped without a transient parent' >&2)

Background

In Linux you can:

• List a group of files with ls Filename*
• Remove a group of files with rm Filename*
• Move a group of files with mv Filename* /New/Directory
• But you cannot copy a group of files with: cp Filename* *.bak

Change Linux cp command to copy group of files

I have a group of files I'd like to copy without entering the names one by one and using the cp command:

$ ls gmail-meta3*
gmail-meta3                          gmail-meta3-REC-1558392194-26467821
gmail-meta3-LAB-1558392194-26467821  gmail-meta3-YAD-1558392194-26467821

How can I use something like the old DOS command copy gmail-meta3* *.bak?

I don't want to type similar command four times:

cp gmail-meta3-LAB-1558392194-26467821 gmail-meta3-LAB-1558392194-26467821.bak

I'm looking for a script/function/app that accepts parameters for old and new filename group and not something with hard-coded filenames. For example, a user can type:

copy gmail-meta3* *.bak

or they might type:

copy gmail-meta3* save-*

I've just lost my phone. I know it's here in my house cause I used it last night and my bluetooth speakers will connect to it this morning.

How can I text my phone using bash? Then the phone notification will sound and I can find my phone.

Note: I asked for a bash solution because it's simpler than installing and configuring a GUI. Also I am more comfortable working in bash than python, HTML, or java, etc. Finally a bash solution works in Windows 10 when you use the Windows Subsystem for Linux (WSL).

Note 2: Reply to comments:

• I don't have a landline so I can't simply call my smartphone.
• It was 6 am on Sunday morning when I lost my phone. People I could email to call my phone were sleeping. I was unsure of the battery charge level and if it died, I could never text it.
• A few weeks previously I had turned off email sound notifications on my smartphone so I couldn't email myself.
• I don't have skype or any VOIP service providers

After 30 minutes I did find the smartphone by texting it using the answer I posted below. It was hidden underneath 4" high-from-floor furniture shelf in the living-room...

There are many questions on automatically mounting or problems encountered during mounting that I've read here. But none on how to manually mount a partition.

Ubuntu 18.04 came out April 26, 2018 and I want to try it to upgrade my programs and convert my data but don't want to commit if there are bugs.

I've shrunk Windows from 410 GB to 385 GB, rebooted Ubuntu 16.04 and ran gparted to create a new 25 GB partition labeled "Ubuntu18.04". I ran rm-kernels and removed about 20 kernels to eliminate about 10 GB on Ubuntu 16.04.

Now I want a script that will populate the new partition with 16.04 LTS and create a new Grub menu option to it. Only relevant directories should be copied. For example /sys, /run, /proc and /dev are virtual directories created during boot and shouldn't be copied.

I also want /etc/fstab patched with the correct UUID and cron reboot jobs disabled such that daily backups on cloned data isn't run after booting the clone.

I anticipate running the script many times over the next few weeks/months. As such the cloning process should effortlessly repeatable.

The same script could be used for testing security updates and new Ubuntu Kernel Team updates without effecting production systems.

I saw a Ubuntu Bash under Windows 10 terminal splash screen here: Windows Subsystem for Linux display Linux distribution?

How can I change my ~/.bashrc to get a similar splash screen in regular Ubuntu that would look like this?:

I would like to display the grub menu from the command line. Also to select a grub boot menu option and press Enter to see what pre-kernel drivers are loaded and the boot parameters passed when loading the kernel.

The reasons to do this from the command line:

• Rebooting to see the grub menu takes time.
• It is awkward to take a picture of the grub menu and post the image on websites. It is easier grabbing a screen shot when Ubuntu is up and running.
• To edit grub menu option with e and take a picture is often difficult because screen is hard to read. With this function you could copy and paste instead.
• It might be easier using this function to reveal all kernel versions rather than apt list --installed | grep linux-image or ls /boot/vml*.
• To quickly see the grub menu number is valuable for grub-reboot and grub-set-default commands.

How can I paint the grub menu from the command line, see internal grub menu entry numbers and display the boot parameters for a given option?

Background: More red / Less blue at night

To save the eyes at night, adding more red and/or subtracting blue, is becoming popular in Windows 10 (blue-light filter) and Linux; Gnome Desktop (Night Light) and Ubuntu Unity Desktop with add-ons such as Red Shift or f.lux.

I'm wondering how to accomplish the same with Ubuntu's built-in command line xrandr <monitor> --gamma 1:1:1 feature. The 1:1:1 represents percentage of red:green:blue. I presume 1 = 100%. I'm not sure if the above packages add more red (1.2:1:1) for ~20% increase or reduce blue (1:1:0.8) for ~20% decrease or both for ~40% change.

Gnome Night Light example doesn't help

According to OMG Ubuntu, within Gnome's Night Light you can use these numerical values:

• 1000 — Lowest value (super warm/red)
• 4000 — Default night light on temperature
• 5500 — Balanced night light temperature
• 6500 — Default night light off temperature
• 10000 — Highest value (super cool/blue)

To test these numerical values, how would does one translate them to override the default --gamma 1:1:1?

What xorg's documentation says

Xorg's documentation doesn't say very much about --gamma controls:

−−gamma red:green:blue

• Set the specified floating point values as gamma correction on the crtc currently attached to this output. Note that you cannot get two different values for cloned outputs (i.e.: which share the same crtc) and that switching an output to another crtc doesn’t change the crtc gamma corrections at all.

Floating decimal points will be helpful because the script I want to upgrade sets xbacklight brightness slowly once a minute over a 90 to 120 minute transition period at dawn and dusk. I want to enhance the script with both xrandr --brightness software support for external monitors and OLED built in displays and xrandr --gamma support for red light / blue light filters. Xorg doesn't say how many decimal positions are supported but I think I think I will set bc calculations should be to 3 or 4 decimal positions for readability / precision balance.

Summary

I'm hoping to mimic what "the big guys" at Microsoft and Gnome are doing with their "more red" and/or "less blue" techniques. I haven't delved into Wayland yet but answers using that system will also be appreciated as it will no doubt be a future concern.

What adjustment to --gamma 1:1:1 are appropriate for night time?

My kernel update crashed this morning and I had to boot to an older kernel. I wanted to see the journal log for the crashed boot so used:

journalctl --list-boots
0 336aa03f15d3443d95e079ad17b6dc77 Fri 2018-02-02 05:49:03 MST—Fri 2018-02-02 17:57:50 MST

It's only showing the current reboot on the older kernel not the kernel update(s) that crashed a few times 10 minutes before.

How can I get persistence across reboots to view previous boot journals?

Please let me know if there is a more appropriate site to post this error. I have a brand new Dell i-7 Skylake laptop, brand new Samsung Pro 960 SSD, New Windows 10 build 16299 (Fall Creators Update released yesterday) just upgraded from build 15063. I downloaded Ubuntu from Windows Store and get this error:

The WSL optional component is not enabled. Please enable it and try again.
See https://aka.ms/wslinstall for details.
Error: 0x8007007e
Press any key to continue...

I googled the recommended site and passed the hex error code with no luck.

Rebooting didn't help.

Any ideas?

When I type the following:

$ IFS=$'\n'; arr=( $(stat "/bin/bash") ); for i in ${arr[@]} ; do echo $i ; done
  File: '/bin/bash'
  Size: 1037528     Blocks: 2032       IO Block: 4096   regular file
Device: 823h/2083d  Inode: 656086      Links: 1
Access: (0755/-rwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2017-05-23 16:38:03.848124217 -0600
Modify: 2017-05-16 06:49:55.000000000 -0600
Change: 2017-05-18 07:43:22.946694155 -0600
 Birth: -

I see the Birth Date for /bin/bash is null / empty. When is this field ever used and what purpose might it have in Linux when it works?

I appreciate there is a shorter way of using stat but this came up during development cycle and I copy and pasted.

I need to test if Bash version number is >= to a specific number. For example I have:

$ bash --version
GNU bash, version 4.3.48(1)-release (x86_64-pc-linux-gnu)
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

In order to use associative arrays the bash version number must be >=4.

In my bash script I'd like to put in a one-liner test in the most elegant / efficient / readable way possible, but other approaches are also accepted.

It's just come to light that there's a $300 ransom you have to pay because ransomware targeting Microsoft Windows has encrypted your data. What steps do Linux users need to protect from this if for example they are using wine?

This ransomware is widely reported to be based on a tool developed by the NSA to hack into computers. The NSA tool was used by a hacker group called the Shadow Brokers. The code can be found in Github.

Microsoft released a patch (MS17-010) against this vulnerability on March 14, 2017. The mass infection is reported to have begun spreading on April 14th. This is discussed here.

As I haven't booted Windows 8.1 in 6 to 8 weeks, can I apply this patch from Ubuntu without booting Windows first? (After research it may be possible ClamAV could report the vulnerability from the Linux side looking into Windows partition but it's unlikely it could apply the patch. The best method would be to reboot into Windows and apply patch MS17-010.)

Individuals and small companies who subscribe to Microsoft Automatic Updates are uninfected. Larger organizations who delay apply patches as they are tested against organization intranets are more likely to be infected.

On May 13, 2017, Microsoft took the extraordinary step of releasing a patch for Windows XP which has been unsupported for 3 years.

No word if wine is doing anything about a security update. It was reported in a comment below that Linux can be infected too when users run wine.

An "accidental hero" registered a domain name that acted as a kill-switch to the ransomware. I presume the non-existent domain was used by the hackers on their private intranet so they didn't infect themselves. Next time they will be smarter so don't rely on this current kill-switch. Installing the Microsoft patch, which prevents exploiting a vulnerability in the SMBv1 protocol, is the best method.

On May 14, 2017 Red Hat Linux said they are not affected by "Wanna Cry" ransomware. This might mislead Ubuntu users along with Red Hat, CentOS, ArchLinux and Fedora users. Red Hat supports wine which answers below confirm can be effected. In essence Ubuntu and other Linux distro users googling this issue might be mislead by the Red Hat Linux Support answer here.

May 15, 2017 Update. Over the last 48 hours Microsoft released patches called KB4012598 for Windows 8, XP, Vista, Server 2008 and Server 2003 to protect against "Wanna Cry" ransomware. These Windows versions are no longer on automatic updates. Although I applied security update MS17-010 on my Windows 8.1 platform yesterday, my old Vista Laptop still needs patch KB4012598 downloaded and manually applied.

Moderator note: This question is not off topic - it asks about whether or not any Linux users need to do any steps for protecting against the risk.

It is perfectly on topic here, because it's relevant to Linux (which Ubuntu is), and it's also relevant for Ubuntu users running Wine or similar compatibility layers, or even VMs on their Ubuntu Linux machines.

When working in the terminal it's inconvenient navigating up to the systray to display the current calendar. Is there a command that will display a calendar from the terminal?

In my daily life I'm always typing <kbd>Keyboard Character</kbd> and I'd like to set up a macro in Ubuntu to automatically enter <kbd> </kbd>.

I'd like to assign it to say Shift+Control+K or whatever keyboard control character combination isn't assigned and already used by Ubuntu.

Back in the day of TSR (Terminate and Stay Resident) MS-DOS programs this was possible. Certainly it must be in Ubuntu too?

Do I have to write a daemon to accomplish this?

I found other questions with no answers: How can I assign macros to my keyboard keys on Ubuntu, similar to Razer Keyboard Macros in Windows?, what is a good mouse/keyboard macro recorder?

I found a similar question with an answer: Can I use Keyboard Shortcuts to implement text macros?. However that question stipulated the answer could not be AutoKey.

In this answer (How can I remove the first line of a file with sed?) there are two ways to delete the first record in a file:

sed '1d' $file >> headerless.txt

** ---------------- OR ----------------**

tail -n +2 $file >> headerless.txt

Personally I think the tail option is cosmetically more pleasing and more readable but probably because I'm sed-challenged.

Which method is fastest?

I've just heard of this bug "Dirty COW" that allows any user with read access to files to also write to them and gain administrative access. How do I protect against this bug?

This is not a duplicate of: askubuntu.../failure-to-download-extra-data-files-flashplugin-installer nor of askubuntu .../how-do-i-stop-failure-to-download-extra-data-files-error-with-pepflashpluginin.

The first link is the closest but the accepted answer does not work.

The Error Screen

The Recommended Solution

sudo apt-get remove --purge flashplugin-installer
sudo apt-get install flashplugin-installer

The new errors from apt-get

Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages were automatically installed and are no longer required:
  bbswitch-dkms dkms libcuda1-361 nvidia-prime
Use 'sudo apt autoremove' to remove them.
Suggested packages:
  x-ttcidfont-conf ttf-bitstream-vera | ttf-dejavu ttf-xfree86-nonfree xfs
The following NEW packages will be installed:
  flashplugin-installer
0 upgraded, 1 newly installed, 0 to remove and 1 not upgraded.
Need to get 6,782 B of archives.
After this operation, 59.4 kB of additional disk space will be used.
Get:1 http://ca.archive.ubuntu.com/ubuntu xenial-updates/multiverse amd64 flashplugin-installer amd64 11.2.202.635ubuntu0.16.04.1 [6,782 B]
Fetched 6,782 B in 0s (17.6 kB/s)                
Preconfiguring packages ...
Selecting previously unselected package flashplugin-installer.
(Reading database ... 336994 files and directories currently installed.)
Preparing to unpack .../flashplugin-installer_11.2.202.635ubuntu0.16.04.1_amd64.deb ...
Unpacking flashplugin-installer (11.2.202.635ubuntu0.16.04.1) ...
Processing triggers for update-notifier-common (3.168.1) ...
flashplugin-installer: downloading http://archive.canonical.com/pool/partner/a/adobe-flashplugin/adobe-flashplugin_20160913.1.orig.tar.gz
Err:1 http://archive.canonical.com/pool/partner/a/adobe-flashplugin/adobe-flashplugin_20160913.1.orig.tar.gz
  Could not open file /var/lib/update-notifier/package-data-downloads/partial/adobe-flashplugin_20160913.1.orig.tar.gz - open (2: No such file or directory) [IP: 91.189.92.191 80]
E: Failed to fetch http://archive.canonical.com/pool/partner/a/adobe-flashplugin/adobe-flashplugin_20160913.1.orig.tar.gz Could not open file /var/lib/update-notifier/package-data-downloads/partial/adobe-flashplugin_20160913.1.orig.tar.gz - open (2: No such file or directory) [IP: 91.189.92.191 80]

E: Download Failed
Setting up flashplugin-installer (11.2.202.635ubuntu0.16.04.1) ...

This problem seems to have ocurred after I removed google-chrome-beta but kept the regular google-chrome. Google chrome works fine for watching TV shows with pepper flash plug-in but it would be nice to keep firefox as a backup browser if chrome goes down. I believe firefox needs the separate flashplugin.

Is there a glitch in canonical somewhere?

Should I just apt-get remove purge flashplugin-installer and not bother apt-get install it again?

PS the ca. prefix on ubuntu.com website name means Canada servers for Canonical and has never been a problem before.