=== Enable remote desktop access to Ubuntu

This works for sure in xubuntu 20.04.  YMMV.

{{{
  $ sudo apt install xrdp
  $ sudo systemctl enable --now xrdp
  $ sudo ufw allow from any to any port 3389 proto tcp
}}}

=== Tunnel for SVN on gauss without VPN

Our server gauss.bu.edu only allows local BU access to SVN etc.  Could use VPN but this is complicated.
Here's a work-around:

{{{
  $ ssh ohm
  $ ssh gauss
  $ ssh -N -R 5432:localhost:80 <home_ip>
}}}

Then 

{{{
   [home] $ svn co http://localhost:5432/svn/botlab.dosi
}}}




=== Close stuck xfce4 session remotely

Do this when x2go connects to a hung xfce4-session, or to solve other issues.

{{{
  $ killall xfce4-session
}}}

=== Install tldr, fd

Suggested by MIT: https://missing.csail.mit.edu/2020/shell-tools/

{{{
  $ sudo apt install tldr
  $ sudo apt install fd-find
  $ ln -s $(which fdfind) ~/.local/bin/fd
  $ sudo apt install ripgrep (provides rg)
  $ sudo apt install fasd
}}}

=== Failed update due to expired debug keys (March 2021)

update fails with something like this:

"[ expired] Ubuntu Debug Symbol Archive Automatic Signing Key (2016)"

See: https://bugs.launchpad.net/ubuntu/+source/ubuntu-keyring/+bug/1920640/comments/3

{{{
Hi,

This is a workaround you can use temporarily:

$ wget -O- http://ddebs.ubuntu.com/dbgsym-release-key.asc | sudo apt-key add -
$ sudo apt update

The key was extended temporarily.
}}}

=== !PulseAudio Sound issues ===

After e.g. using external monitor on Thinkpad, sound stops working.  Only unplugged HDMI is listed as output device in pulseaudio.  Fix is to type:

{{{
  $ pacmd set-card-profile 0 output:analog-stereo
}}}



=== Installing remote printers in Physics ===

To print to e.g. the EDF laser printer:

* Start->Settings->Printers
* Add
* Network Printer->LPD/LPR Host or Printer
 * Host: buphyk.bu.edu
 * Queue: edf or edf-duplex
* For printer driver:
 * Generic
 * Raw Queue

=== Mounting logical volumes on external disks ===

To mount a logical volume on an external (e.g. removed from old machine) disk:
{{{
 $ sudo apt install lvm2    # (if needed)
 $ sudo pvs
  /run/lvm/lvmetad.socket: connect failed: No such file or directory
  WARNING: Failed to connect to lvmetad. Falling back to internal scanning.
  PV         VG         Fmt  Attr PSize   PFree
  /dev/sdb5  xubuntu-vg lvm2 a--  465.28g    0 
}}}
Note the name {{{xubuntu-vg}}}.
{{{
 $sudo lvdisplay xubuntu-vg
  /run/lvm/lvmetad.socket: connect failed: No such file or directory
  WARNING: Failed to connect to lvmetad. Falling back to internal scanning.
  --- Logical volume ---
  LV Path                /dev/xubuntu-vg/root
  LV Name                root
  VG Name                xubuntu-vg
  LV UUID                xXguet-eimr-l0Y4-dGjb-2wQ4-6nba-4jHBqr
  LV Write Access        read/write
  LV Creation host, time xubuntu, 2016-10-26 14:07:10 -0400
  LV Status              available
  # open                 1
  LV Size                457.48 GiB
  Current LE             117114
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:0
}}}   
Note the path {{{/dev/xubuntu-vg/root}}}.
{{{
  $ sudo lvchange -ay /dev/xubuntu-vg/root
  $ sudo mount /dev/xubuntu-vg/root /mnt
}}}
(whew!)


=== Installing/updating !VirtualBox

As of about 2018-02-01 an Ubuntu 16.04 security update badly crashes VB causing kernel module corruption on my machine so nothing worked afterwards.  Fixed borked kernel modules with:
{{{
  $ sudo dpkg-reconfigure linux-image-`uname -r`
}}}

Then clean up and reinstall VB with:
{{{
  $ sudo apt purge virtualbox*
  $ sudo apt install virtualbox-5.2 dkms
  $ VBoxManage extpack install .....vbox-extpack
}}}

(download the extension pack from https://www.virtualbox.org/wiki/Downloads)

=== Fix ctrl+space

The package "ibus" which provides international keyboard input steals ctrl+space so it doesn't work to set the mark in emacs.  Some googling reveals that the configuration settings for this package are confusing/broken, so best to remove it:

{{{
sudo apt-get purge ibus
sudo killall ibus
}}}

=== Changing Keyboard Mapping

'''Undid all this''' June 2018 because it interacts badly with VirtualBox, rdesktop etc

How to permanently change keyboard mapping in Ubuntu 14 (and later).
Apparently they stopped using '''xmodmap''' a while ago.

First, to get rid of "Caps Lock" and make it an alternative Ctrl key,
edit {{{/etc/default/keyboard}}} and edit line to read:
{{{
  XKBOPTIONS="ctrl:nocaps"
}}}

(can also use "ctrl:swapcaps" if you want to keep caps lock where CTRL is)

Second, to swap ESC and !Tilde/Backquote keys (for a PC105/US-english setup):

Edit {{{/usr/share/X11/xkb/symbols/pc}}}:
{{{
  key <ESC> {[  Escape ] };
change to:
  key <ESC> {[ quoteleft,   asciitilde     ]   };
}}}

Edit {{{/usr/share/X11/xkb/symbols/us}}}:
{{{
  key <TLDE> {      [     grave,    asciitilde      ]       };
change to:
  key <TLDE> {[  Escape    ] };
}}}

Then {{{sudo dpkg-reconfigure keyboard-configuration}}} and select
"Generic 105-key (Intl) PC", "English (US)", "English (US)", "Yes".

=== Change Ethernet device to eth0 ===

Create file {{{/etc/udev/rules.d/70-persistent-net.rules}}} containing a line like:
{{{
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:b5:6d:04:82:96", ATTR{dev_id}=="0x0", ATTR{type}=="1", NAME="eth0"
}}}

This works for USB ethernet dongle on Thinkpad laptop, at least.