Byte Commander's questions

I am horribly impatient and can't stand the (for me subjectively long) delay of around 2 seconds after entering an incorrect password in the login screen or also as sudo password, before I can retry typing it correctly.

Is there a way to modify the delay and reduce it to around half a second or turn it completely off, both for sudo and the login screen?

The optimal solution would include a longer delay after maybe 3 or 5 incorrect passwords, to still prevent brute-forcing.

PS: I am currently using vanilla Ubuntu 16.04 with Unity Desktop and lightdm.

For those who like humour, sudo can be configured to print a random more or less insulting or funny phrase instead of the neutral Sorry, try again. by adding the line below to /etc/sudoers (using the command sudo visudo, not editing manually!):

Defaults insults

Here are some examples:

[sudo] password for bytecommander: 
The more you drive -- the dumber you get.
[sudo] password for bytecommander: 
I've seen penguins that can type better than that.
[sudo] password for bytecommander: 
This mission is too important for me to allow you to jeopardize it.
[sudo] password for bytecommander: 
He has fallen in the water!
[sudo] password for bytecommander: 
Hold it up to the light --- not a brain in sight!

Now just for fun I'd like to read through all of them, but entering wrong passwords all day is not really the best method (delay after each attempt, only 2 messages per 3 attempts, abort after 3 attempts, ...).

So... where are these insults actually stored? Any plain text file I can directly read? Or hard coded strings in the source code?

How can I get a list of all available sudo insult messages?

When I run a kernel or NVIDIA driver update on my 16.04, this triggers an initramfs rebuild which outputs the warning below:

Processing triggers for initramfs-tools (0.122ubuntu8.1) ...
update-initramfs: Generating /boot/initrd.img-4.4.0-34-generic
W: Possible missing firmware /lib/firmware/i915/skl_guc_ver6.bin for module i915_bpo

I have a notebook with two graphics chips, an NVIDIA GeForce 940M and the Intel i5-6200U's integrated graphics.

The device in use is my NVIDIA card:

$ inxi -G
Graphics:  Card-1: Intel Sky Lake Integrated Graphics
           Card-2: NVIDIA GM108M [GeForce 940M]
           Display Server: X.Org 1.18.3 driver: nvidia Resolution: [email protected]
           GLX Renderer: GeForce 940M/PCIe/SSE2 GLX Version: 4.5.0 NVIDIA 367.35

Here's the output of lshw -c video, corresponding to my Intel graphics chip which should use that driver:

    *-display         
         description: VGA compatible controller
         product: Sky Lake Integrated Graphics
         vendor: Intel Corporation
         physical id: 2
         bus info: pci@0000:00:02.0
         version: 07
         width: 64 bits
         clock: 33MHz
         capabilities: pciexpress msi pm vga_controller bus_master cap_list rom
         configuration: driver=i915_bpo latency=0
         resources: irq:125 memory:a2000000-a2ffffff memory:b0000000-bfffffff ioport:5000(size=64)

The file in the warning does not exist, only those:

$ ll /lib/firmware/i915/
total 336
drwxr-xr-x  2 root root   4096 Aug 11 13:24 ./
drwxr-xr-x 74 root root  32768 Aug 11 13:24 ../
-rw-r--r--  1 root root   5872 Jul 21 17:03 bxt_dmc_ver1_04.bin
-rw-r--r--  1 root root   5872 Jul 21 17:03 bxt_dmc_ver1_05.bin
-rw-r--r--  1 root root   8380 Jul 21 17:03 bxt_dmc_ver1_06.bin
-rw-r--r--  1 root root   8380 Jul 21 17:05 bxt_dmc_ver1_07.bin
lrwxrwxrwx  1 root root     19 Jul 21 17:05 bxt_dmc_ver1.bin -> bxt_dmc_ver1_07.bin
-rw-r--r--  1 root root   8824 Jul 21 17:03 skl_dmc_ver1_23.bin
-rw-r--r--  1 root root   8928 Jul 12 21:33 skl_dmc_ver1_26.bin
lrwxrwxrwx  1 root root     19 Jul 12 21:33 skl_dmc_ver1.bin -> skl_dmc_ver1_26.bin
-rw-r--r--  1 root root 109636 Jul 21 17:03 skl_guc_ver1_1059.bin
lrwxrwxrwx  1 root root     21 Jul 21 17:03 skl_guc_ver1.bin -> skl_guc_ver1_1059.bin
-rw-r--r--  1 root root 128320 Jul 21 17:03 skl_guc_ver4_3.bin
lrwxrwxrwx  1 root root     18 Jul 21 17:03 skl_guc_ver4.bin -> skl_guc_ver4_3.bin

The latest driver package seems to be installed though:

$ apt-cache policy xserver-xorg-video-intel
xserver-xorg-video-intel:
  Installed: 2:2.99.917+git20160325-1ubuntu1
  Candidate: 2:2.99.917+git20160325-1ubuntu1
  Version table:
 *** 2:2.99.917+git20160325-1ubuntu1 500
        500 http://ftp.uni-stuttgart.de/ubuntu xenial/main amd64 Packages
        100 /var/lib/dpkg/status

What does this warning mean exactly and how can I fix it?

When trying to securely wipe SSDs, we have several problems:

• SSDs wear out after a limited amount of erase cycles
• SSDs have a controller that dynamically maps LBAs (logical block addresses used by the system to access the disk) to NVRAM cells (the actual flash memory cells) to balance the wear, which means telling the disk to overwrite the blocks that formerly stored a specific file may result in overwriting any other spare blocks.
• SSDs have a notable percentage of reserve capacity that is used to compensate dying storage cells and reduce wearing. They are not visible to the system and might hold old data fragments.

Now what options do we have from inside Ubuntu to securely wipe SSDs?

I've heard that some newer SSDs should be able to securely wipe themselves, but how do I find out whether my SSD is capable of this and how would I trigger it?
There should also be an ATA secure erase command, how do I find out if that is supported and how would I trigger that?

Are there also ways to securely wipe only a given file or only unused space?
I guess making a backup of all partitions, securely wiping the entire disk and then restoring the backup would be possible but sounds too complicated and would take too long to be practical. Are there other alternatives? If not, what tools can I use to backup partitions without also backing up already deleted files?

Of course the standard tools like shred or wipe are not usable here for the points described above. They simply overwrite a a file (by overwriting its file system clusters which are bound to LBAs which are not constantly pointing on the same flash cells due to the wear levelling controller).

For whatever reason, we do no longer need to be root (or using sudo) to run /sbin/shutdown, /sbin/reboot etc.

This seems to be because those executables are now symlinks to /bin/systemctl which handles everything as normal user.

However, what if I want shutdown and reboot to require root authentication again? How can I achieve this?

I wanted to install the Microsoft fonts on 16.04 and ran the command below, but there are many errors (or only warnings?) about that the user _apt has no permissions on the downloaded .exe files.

Command:

sudo apt install ttf-mscorefont-installer

Error message (repeated for every downloaded font exe):

ttf-mscorefonts-installer: downloading http://downloads.sourceforge.net/corefonts/andale32.exe
Get:1 http://downloads.sourceforge.net/corefonts/andale32.exe [198 kB]
Fetched 198 kB in 1s (180 kB/s)                                                              
W: Can't drop privileges for downloading as file '/var/lib/update-notifier/package-data-downloads/partial/andale32.exe' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)

But in the end it still says that the installation was successful. So is this just a bug in the package's install scripts, or is anything wrong on my side here? Do I need to take any further actions?

Full output (the original output was the same as with --reinstall):

$ sudo apt install --reinstall ttf-mscorefonts-installer 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
0 to upgrade, 0 to newly install, 1 reinstalled, 0 to remove and 4 not to upgrade.
Need to get 29,5 kB of archives.
After this operation, 0 B of additional disk space will be used.
Get:1 http://ftp.uni-stuttgart.de/ubuntu xenial/multiverse amd64 ttf-mscorefonts-installer all 3.4+nmu1ubuntu2 [29,5 kB]
Fetched 29,5 kB in 0s (280 kB/s)                     
Preconfiguring packages ...
(Reading database ... 214933 files and directories currently installed.)
Preparing to unpack .../ttf-mscorefonts-installer_3.4+nmu1ubuntu2_all.deb ...
mscorefonts-eula license has already been accepted
Unpacking ttf-mscorefonts-installer (3.4+nmu1ubuntu2) over (3.4+nmu1ubuntu2) ...
Processing triggers for fontconfig (2.11.94-0ubuntu1) ...
Processing triggers for update-notifier-common (3.168) ...
ttf-mscorefonts-installer: downloading http://downloads.sourceforge.net/corefonts/andale32.exe
Get:1 http://downloads.sourceforge.net/corefonts/andale32.exe [198 kB]
Fetched 198 kB in 1s (180 kB/s)                                                              
W: Can't drop privileges for downloading as file '/var/lib/update-notifier/package-data-downloads/partial/andale32.exe' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)
ttf-mscorefonts-installer: downloading http://downloads.sourceforge.net/corefonts/arial32.exe
Get:1 http://downloads.sourceforge.net/corefonts/arial32.exe [554 kB]
Fetched 554 kB in 1s (466 kB/s)                                                             
W: Can't drop privileges for downloading as file '/var/lib/update-notifier/package-data-downloads/partial/arial32.exe' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)
ttf-mscorefonts-installer: downloading http://downloads.sourceforge.net/corefonts/arialb32.exe
Get:1 http://downloads.sourceforge.net/corefonts/arialb32.exe [168 kB]
Fetched 168 kB in 0s (169 kB/s)                                                              
W: Can't drop privileges for downloading as file '/var/lib/update-notifier/package-data-downloads/partial/arialb32.exe' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)
ttf-mscorefonts-installer: downloading http://downloads.sourceforge.net/corefonts/comic32.exe
Get:1 http://downloads.sourceforge.net/corefonts/comic32.exe [246 kB]
Fetched 246 kB in 1s (224 kB/s)                                                             
W: Can't drop privileges for downloading as file '/var/lib/update-notifier/package-data-downloads/partial/comic32.exe' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)
ttf-mscorefonts-installer: downloading http://downloads.sourceforge.net/corefonts/courie32.exe
Get:1 http://downloads.sourceforge.net/corefonts/courie32.exe [646 kB]
Fetched 646 kB in 1s (472 kB/s)                                                               
W: Can't drop privileges for downloading as file '/var/lib/update-notifier/package-data-downloads/partial/courie32.exe' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)
ttf-mscorefonts-installer: downloading http://downloads.sourceforge.net/corefonts/georgi32.exe
Get:1 http://downloads.sourceforge.net/corefonts/georgi32.exe [392 kB]
Fetched 392 kB in 1s (364 kB/s)                                                              
W: Can't drop privileges for downloading as file '/var/lib/update-notifier/package-data-downloads/partial/georgi32.exe' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)
ttf-mscorefonts-installer: downloading http://downloads.sourceforge.net/corefonts/impact32.exe
Get:1 http://downloads.sourceforge.net/corefonts/impact32.exe [173 kB]
Fetched 173 kB in 0s (176 kB/s)                                                              
W: Can't drop privileges for downloading as file '/var/lib/update-notifier/package-data-downloads/partial/impact32.exe' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)
ttf-mscorefonts-installer: downloading http://downloads.sourceforge.net/corefonts/times32.exe
Get:1 http://downloads.sourceforge.net/corefonts/times32.exe [662 kB]
Fetched 662 kB in 2s (235 kB/s)                                                              
W: Can't drop privileges for downloading as file '/var/lib/update-notifier/package-data-downloads/partial/times32.exe' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)
ttf-mscorefonts-installer: downloading http://downloads.sourceforge.net/corefonts/trebuc32.exe
Get:1 http://downloads.sourceforge.net/corefonts/trebuc32.exe [357 kB]
Fetched 357 kB in 1s (307 kB/s)                                                              
W: Can't drop privileges for downloading as file '/var/lib/update-notifier/package-data-downloads/partial/trebuc32.exe' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)
ttf-mscorefonts-installer: downloading http://downloads.sourceforge.net/corefonts/verdan32.exe
Get:1 http://downloads.sourceforge.net/corefonts/verdan32.exe [352 kB]
Fetched 352 kB in 4s (85,7 kB/s)                                                             
W: Can't drop privileges for downloading as file '/var/lib/update-notifier/package-data-downloads/partial/verdan32.exe' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)
ttf-mscorefonts-installer: downloading http://downloads.sourceforge.net/corefonts/webdin32.exe
Get:1 http://downloads.sourceforge.net/corefonts/webdin32.exe [185 kB]
Fetched 185 kB in 0s (210 kB/s)                                                              
W: Can't drop privileges for downloading as file '/var/lib/update-notifier/package-data-downloads/partial/webdin32.exe' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)

These fonts were provided by Microsoft "in the interest of cross-
platform compatibility".  This is no longer the case, but they are
still available from third parties.

You are free to download these fonts and use them for your own use,
but you may not redistribute them in modified form, including changes
to the file name or packaging format.

Extracting cabinet: /var/lib/update-notifier/package-data-downloads/partial/andale32.exe
  extracting fontinst.inf
  extracting andale.inf
  extracting fontinst.exe
  extracting AndaleMo.TTF
  extracting ADVPACK.DLL
  extracting W95INF32.DLL
  extracting W95INF16.DLL

All done, no errors.
Extracting cabinet: /var/lib/update-notifier/package-data-downloads/partial/arial32.exe
  extracting FONTINST.EXE
  extracting fontinst.inf
  extracting Ariali.TTF
  extracting Arialbd.TTF
  extracting Arialbi.TTF
  extracting Arial.TTF

All done, no errors.
Extracting cabinet: /var/lib/update-notifier/package-data-downloads/partial/arialb32.exe
  extracting fontinst.exe
  extracting fontinst.inf
  extracting AriBlk.TTF

All done, no errors.
Extracting cabinet: /var/lib/update-notifier/package-data-downloads/partial/comic32.exe
  extracting fontinst.inf
  extracting Comicbd.TTF
  extracting Comic.TTF
  extracting fontinst.exe

All done, no errors.
Extracting cabinet: /var/lib/update-notifier/package-data-downloads/partial/courie32.exe
  extracting cour.ttf
  extracting courbd.ttf
  extracting courbi.ttf
  extracting fontinst.inf
  extracting couri.ttf
  extracting fontinst.exe

All done, no errors.
Extracting cabinet: /var/lib/update-notifier/package-data-downloads/partial/georgi32.exe
  extracting fontinst.inf
  extracting Georgiaz.TTF
  extracting Georgiab.TTF
  extracting Georgiai.TTF
  extracting Georgia.TTF
  extracting fontinst.exe

All done, no errors.
Extracting cabinet: /var/lib/update-notifier/package-data-downloads/partial/impact32.exe
  extracting fontinst.exe
  extracting Impact.TTF
  extracting fontinst.inf

All done, no errors.
Extracting cabinet: /var/lib/update-notifier/package-data-downloads/partial/times32.exe
  extracting fontinst.inf
  extracting Times.TTF
  extracting Timesbd.TTF
  extracting Timesbi.TTF
  extracting Timesi.TTF
  extracting FONTINST.EXE

All done, no errors.
Extracting cabinet: /var/lib/update-notifier/package-data-downloads/partial/trebuc32.exe
  extracting FONTINST.EXE
  extracting trebuc.ttf
  extracting Trebucbd.ttf
  extracting trebucbi.ttf
  extracting trebucit.ttf
  extracting fontinst.inf

All done, no errors.
Extracting cabinet: /var/lib/update-notifier/package-data-downloads/partial/verdan32.exe
  extracting fontinst.exe
  extracting fontinst.inf
  extracting Verdanab.TTF
  extracting Verdanai.TTF
  extracting Verdanaz.TTF
  extracting Verdana.TTF

All done, no errors.
Extracting cabinet: /var/lib/update-notifier/package-data-downloads/partial/webdin32.exe
  extracting fontinst.exe
  extracting Webdings.TTF
  extracting fontinst.inf
  extracting Licen.TXT

All done, no errors.
All fonts downloaded and installed.
Setting up ttf-mscorefonts-installer (3.4+nmu1ubuntu2) ...

I'm running Ubuntu 16.04 Xenial desktop, 64 bit, and wanted to install openjdk-9-jdk (Java 9 development kit). The version available from the universe repository is 9~b114-0ubuntu1.

Running the installation command successfully installs the dependencies (see below, including package openjdk-9-jdk-headless), but fails to install the requested package itself because of a file provided by said dependency that is also present in the problematic package:

dpkg: error processing archive /var/cache/apt/archives/openjdk-9-jdk_9~b114-0ubuntu1_amd64.deb (--unpack):
 trying to overwrite '/usr/lib/jvm/java-9-openjdk-amd64/include/linux/jawt_md.h', which is also in package openjdk-9-jdk-headless:amd64 9~b114-0ubuntu1

Here's the full output:

$ sudo apt install openjdk-9-jdk
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following additional packages will be installed:
  ca-certificates-java libice-dev libpthread-stubs0-dev libsm-dev libx11-dev libx11-doc libxau-dev libxcb1-dev libxdmcp-dev
  libxt-dev openjdk-9-jdk-headless openjdk-9-jre openjdk-9-jre-headless x11proto-core-dev x11proto-input-dev x11proto-kb-dev
  xorg-sgml-doctools xtrans-dev
Suggested packages:
  libice-doc libsm-doc libxcb-doc libxt-doc openjdk-9-demo openjdk-9-source visualvm icedtea-8-plugin fonts-ipafont-gothic
  fonts-ipafont-mincho ttf-wqy-microhei | ttf-wqy-zenhei fonts-indic
The following NEW packages will be installed
  ca-certificates-java libice-dev libpthread-stubs0-dev libsm-dev libx11-dev libx11-doc libxau-dev libxcb1-dev libxdmcp-dev
  libxt-dev openjdk-9-jdk openjdk-9-jdk-headless openjdk-9-jre openjdk-9-jre-headless x11proto-core-dev x11proto-input-dev
  x11proto-kb-dev xorg-sgml-doctools xtrans-dev
0 to upgrade, 19 to newly install, 0 to remove and 0 not to upgrade.
Need to get 183 MB/187 MB of archives.
After this operation, 326 MB of additional disk space will be used.
Do you want to continue? [Y/n] 
Get:1 http://ftp.uni-stuttgart.de/ubuntu xenial/main amd64 ca-certificates-java all 20160321 [12,9 kB]
Get:2 http://ftp.uni-stuttgart.de/ubuntu xenial/universe amd64 openjdk-9-jre-headless amd64 9~b114-0ubuntu1 [183 MB]
Get:3 http://ftp.uni-stuttgart.de/ubuntu xenial/universe amd64 openjdk-9-jre amd64 9~b114-0ubuntu1 [51,5 kB]                       
Fetched 183 MB in 2min 21s (1.293 kB/s)                                                                                            
Selecting previously unselected package ca-certificates-java.
(Reading database ... 210101 files and directories currently installed.)
Preparing to unpack .../ca-certificates-java_20160321_all.deb ...
Unpacking ca-certificates-java (20160321) ...
Selecting previously unselected package openjdk-9-jre-headless:amd64.
Preparing to unpack .../openjdk-9-jre-headless_9~b114-0ubuntu1_amd64.deb ...
Unpacking openjdk-9-jre-headless:amd64 (9~b114-0ubuntu1) ...
Selecting previously unselected package xorg-sgml-doctools.
Preparing to unpack .../xorg-sgml-doctools_1%3a1.11-1_all.deb ...
Unpacking xorg-sgml-doctools (1:1.11-1) ...
Selecting previously unselected package x11proto-core-dev.
Preparing to unpack .../x11proto-core-dev_7.0.28-2ubuntu1_all.deb ...
Unpacking x11proto-core-dev (7.0.28-2ubuntu1) ...
Selecting previously unselected package libice-dev:amd64.
Preparing to unpack .../libice-dev_2%3a1.0.9-1_amd64.deb ...
Unpacking libice-dev:amd64 (2:1.0.9-1) ...
Selecting previously unselected package libpthread-stubs0-dev:amd64.
Preparing to unpack .../libpthread-stubs0-dev_0.3-4_amd64.deb ...
Unpacking libpthread-stubs0-dev:amd64 (0.3-4) ...
Selecting previously unselected package libsm-dev:amd64.
Preparing to unpack .../libsm-dev_2%3a1.2.2-1_amd64.deb ...
Unpacking libsm-dev:amd64 (2:1.2.2-1) ...
Selecting previously unselected package libxau-dev:amd64.
Preparing to unpack .../libxau-dev_1%3a1.0.8-1_amd64.deb ...
Unpacking libxau-dev:amd64 (1:1.0.8-1) ...
Selecting previously unselected package libxdmcp-dev:amd64.
Preparing to unpack .../libxdmcp-dev_1%3a1.1.2-1.1_amd64.deb ...
Unpacking libxdmcp-dev:amd64 (1:1.1.2-1.1) ...
Selecting previously unselected package x11proto-input-dev.
Preparing to unpack .../x11proto-input-dev_2.3.1-1_all.deb ...
Unpacking x11proto-input-dev (2.3.1-1) ...
Selecting previously unselected package x11proto-kb-dev.
Preparing to unpack .../x11proto-kb-dev_1.0.7-0ubuntu1_all.deb ...
Unpacking x11proto-kb-dev (1.0.7-0ubuntu1) ...
Selecting previously unselected package xtrans-dev.
Preparing to unpack .../xtrans-dev_1.3.5-1_all.deb ...
Unpacking xtrans-dev (1.3.5-1) ...
Selecting previously unselected package libxcb1-dev:amd64.
Preparing to unpack .../libxcb1-dev_1.11.1-1ubuntu1_amd64.deb ...
Unpacking libxcb1-dev:amd64 (1.11.1-1ubuntu1) ...
Selecting previously unselected package libx11-dev:amd64.
Preparing to unpack .../libx11-dev_2%3a1.6.3-1ubuntu2_amd64.deb ...
Unpacking libx11-dev:amd64 (2:1.6.3-1ubuntu2) ...
Selecting previously unselected package libx11-doc.
Preparing to unpack .../libx11-doc_2%3a1.6.3-1ubuntu2_all.deb ...
Unpacking libx11-doc (2:1.6.3-1ubuntu2) ...
Selecting previously unselected package libxt-dev:amd64.
Preparing to unpack .../libxt-dev_1%3a1.1.5-0ubuntu1_amd64.deb ...
Unpacking libxt-dev:amd64 (1:1.1.5-0ubuntu1) ...
Selecting previously unselected package openjdk-9-jre:amd64.
Preparing to unpack .../openjdk-9-jre_9~b114-0ubuntu1_amd64.deb ...
Unpacking openjdk-9-jre:amd64 (9~b114-0ubuntu1) ...
Selecting previously unselected package openjdk-9-jdk-headless:amd64.
Preparing to unpack .../openjdk-9-jdk-headless_9~b114-0ubuntu1_amd64.deb ...
Unpacking openjdk-9-jdk-headless:amd64 (9~b114-0ubuntu1) ...
Preparing to unpack .../openjdk-9-jdk_9~b114-0ubuntu1_amd64.deb ...
Unpacking openjdk-9-jdk:amd64 (9~b114-0ubuntu1) ...
dpkg: error processing archive /var/cache/apt/archives/openjdk-9-jdk_9~b114-0ubuntu1_amd64.deb (--unpack):
 trying to overwrite '/usr/lib/jvm/java-9-openjdk-amd64/include/linux/jawt_md.h', which is also in package openjdk-9-jdk-headless:amd64 9~b114-0ubuntu1
Processing triggers for ca-certificates (20160104ubuntu1) ...
Updating certificates in /etc/ssl/certs...
0 added, 0 removed; done.
Running hooks in /etc/ca-certificates/update.d...
done.
Processing triggers for man-db (2.7.5-1) ...
Processing triggers for gnome-menus (3.13.3-6ubuntu3) ...
Processing triggers for desktop-file-utils (0.22-1ubuntu5) ...
Processing triggers for bamfdaemon (0.5.3~bzr0+16.04.20160415-0ubuntu1) ...
Rebuilding /usr/share/applications/bamf-2.index...
Processing triggers for mime-support (3.59ubuntu1) ...
Processing triggers for hicolor-icon-theme (0.15-0ubuntu1) ...
Errors were encountered while processing:
 /var/cache/apt/archives/openjdk-9-jdk_9~b114-0ubuntu1_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)

So obviously this seems to be a bug and caused by incorrect packaging and not a fault on my side. There also are some related bug reports on Launchpad already, like e.g. this report which seems to be the most important one. I subscribed to that report, but there's no solution for Xenial yet.

Therefore my question here is not about this packaging bug, but how to work around this and install openjdk-9-jdk anyway, ignoring the "trying to overwrite file" error?

There are two command-line tools (in two different packages) to access the X clipboard:

• xclip
• xsel

I would love to know the difference between those two and hear a recommendation which one to use in which cases.

I want to see what icons are installed and available on my system and by which names I have to refer to them.

How can I get a nicely formatted list of all unique icons (don't show several resolutions separately) that contains the icon name, a preview thumbnail, the location and maybe if possible where it came from (e.g. which icon theme package)?

System: Ubuntu 15.10 Wily Werewolf 64 bit
Desktop: Unity

I have a list of packages on my system, that were installed and removed again, but not purged, i.e. there are still a lot of conffiles etc. laying around.

The output of dpkg --get-selections | grep deinstall lists about 85 different packages which I don't need and want to be purged entirely.

So my short question, which I decided to finally ask after experimenting around has lead to this problem, is:

How do I completely purge previously installed packages that are already removed?

Reinstalling and then purging is not an option, of course.

I was in the situation that an application I had was not available in the Unity applications lens after I removed a custom .desktop launcher file in my home directory that had overridden the system-wide one.

My problem was that I needed to apply those changes and update in this case the database of installed .desktop files, but other similar scenarios are also imaginable.

So what could I have done (and do the next time) instead of rebooting or logging out and back in to update the Unity configuration and force it to reload and reinitialize all of its stuff?

I am on 15.10, so unity --reset & does not work because it's deprecated.

I then tried unity --replace & instead, but that crashed my desktop and rendered my TTY7 unusable. It first flashed dark and looked like it was restarting Unity and restoring the desktop, but then it did not react to anything any more. Switching to TTY1 and back left me with a black screen plus mouse cursor. After rebooting via TTY1 login and reboot, it worked again and Unity even recognized my application now.

But if I would have been in a situation where a reboot or logout was no option, what would have been my way to go?

I want to sign some Python code files I wrote, because they are plug-in modules for one of my projects. For distributing it, I want that the user can be sure a plug-in is verified and safe (because written by me or somebody I trust) and was not modified.

The software is just a open-source hobby project, therefore I don't want to spend any money for buying an official certificate. Instead, I assume that the main program is always valid and can be trusted without additional verification. If somebody downloads it from any other location than my GitHub repository, it's their fault.

From what I've read, signing is usually done by creating an asymmetric key pair, calculating a strong cryptographic hash value (e.g. SHA-512) from the code file, encrypting the hash using my private key and storing that signature in a separate file to be shipped with the original code file.
The main program will then have to decrypt the signature using the public key that is saved in plain-text in the main program's source code, calculate the same hash function of the code file and then compare it to the decrypted one. If they match, the plug-in can be trusted.

So now my question:

How do I easily create a strong asymmetric key pair with Ubuntu tools and how do I easily calculate a cryptographic hash value of a file?
Automatizing the signing process in a script (using always the same key) would be great.

According to How can PPAs be removed? there are mainly 3 methods to get rid of a PPA:

• Use the add-apt-repository command:

  sudo add-apt-repository --remove ppa:???/???
  

• Manually remove the .list file:

  sudo rm /etc/apt/sources.list.d/????.list
  

• Use additional tools like e.g. ppa-purge... (not topic of this question)

I am curious what the difference between the first and second option is, i.e. is there anything more that add-apt-repository --remove does, compared to just deleting the .list file?

One example I could think of would be GPG keys that were installed together with the PPA. Will add-apt-repository handle and remove them in contrast to just rm-ing the .list file?

_{Please note that neither removing GPG keys nor using ppa-purge is the topic of this question!}

I have played around a lot with my Python installations (2 and 3) and installed a bunch of packages, some using apt-get, but most using pip. I have also upgraded many apt-installed packages with pip to a newer version.

My question is:
How can I reverse all those changes, remove all pip-installed Python packages and just keep the default set of preinstalled packages in their default repository version, plus those installed by apt-get but only as dependency of other software, always downgrading to the repository version if necessary.

I want to do this to have a tidied up Python environment for the system and have my modifications in virtualenvs only.

Is that possible without a system reinstall? How would I approach it?

Since the installation, I have added not too few PPAs to my 15.04 system because I wanted a specific application. But sometimes I have removed that package later again, because it did not work, was not what I really wanted, or just because I don't need it any more. I don't know if that makes a difference, but some repositories were installed with add-apt-repository while others just came by a command that just created the file in /etc/apt/sources.list.d/ manually.

Now how can I check whether I have any packages from a PPA installed and if not, remove it from my software sources? This procedure should automatically work through all PPAs.

I often see users that try to fix an issue and somewhere read or just try to recursively chown their home directory and sometimes even also reset permissions recursively to something like rwxr-xr-x or similar.

Imagine such an owner/permission massacre - are there critical files/directories that need special permissions or to be root-owned for the system to work?

There are the commands find and locate to search for files on the disk.

I know that find recursively processes all needed subdirectories to search files and therefore is slow but up-to-date, whereas locate uses a database that gets updated every now and then (when exactly?) to quickly show results which might be outdated though.

Are there any other differences? In which situations would one prefer the one or the other? And when does the locate database get updated usually?

When running top, I can see this (shortened) example output:

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
 4586 ipc-adm+  20   0 1303900 605152  92844 S  30,6 29,3   3:52.88 firefox
 3985 ipc-adm+  20   0  258588 124508  63072 S  12,2  6,0   0:40.04 compiz
 3092 root      20   0  172392  56164  25980 S   6,1  2,7   0:30.13 Xorg

There are two values that I am interested in: PR (Priority) and NI (Niceness).

If I understood what I already found out correctly, both determine how much CPU time a process will get in contrast to other processes. But what is the difference between those values then?

Could you also please describe how to manipulate those values of a process and under which circumstances this might be useful?

Let's assume I have a foreign text document I open with a text editing tool that recognizes fonts (e.g. LibreOffice Writer). In this document, there might be some fonts used that are not available on my Ubuntu installation (e.g. Garamond).

The question is: How does Ubuntu decide which one of the installed fonts to use as replacement for the unknown font? Does it read any of the font's characteristics and look for a similar one? Is a default substitution font always used? Does it search for similar font names?

Additional to that, I would like to know if I can somehow change this behavior or set manual font aliases to automatically use e.g. the free font EB-Garamont instead of the non-free Garamont?

I often read that one should not place swap partitions on a SSD drive, as this may harm the device. Is this true? Can you please explain the reason to me?

Because I otherwise would have thought that placing swap on an SSD is the best choice, as it's much faster than HDDs and therefore swapping RAM contents to the SSD is not as slow as it would be with the HDD...