Garmin SubMusic (on Ubuntu 18.04)

1. Install dependencies
2. Install Nextcloud
3. Install Music
4. Install Ampache
5. Install Garmin SubMusic

Nextcloud

Reference guide

Nextcloud 19 dependencies:

• PHP >=7.2
• MySQL/MariaDB
• Nginx

Ampache dependencies:

• PHP >=7.2
• MySQL/MariaDB
• Nginx
• Composer

Run GUI application from chroot

xhost +local:
sudo chroot /mnt
export DISPLAY=:0
gedit

Gedit transparent background

Some gnome applications (usual ones: gedit, gnome-calculator) can suddenly get looking incorrect (transparent background, visual artifacts, etc).

The reason could be a change in:
- Settings => Region & Language => Manage Installed Languages => Keyboard input method system
- Language Support => Keyboard input method system

Solution:

- remove ~/.xinputrc
- reboot

`Error! Could not locate dkms.conf file`

- adapt /usr/sbin/dkms script 

to be more informative when error logging. You can change the line 527 (or similar on your system):

[[ -r $read_conf_file ]] || die 4 $"Could not locate dkms.conf file." \

to something like

[[ -r $read_conf_file ]] || die 4 $"Could not locate $read_conf_file file." \

to see where exactly is the problem located.

- dkms status

There should be valid output, without error messages.
If any dkms.conf file is not found:
- investigate sources and configs existing in the system (see commands below)
- remove "bad" modules (e.g. sudo rm -rf /var/lib/dkms/nvidia/)
- rebuild existing dkms modules

- ls -l /var/lib/dkms

to know what dkms modules are in the system

- ls /usr/src/*/dkms.conf

check existing dkms config files

- sudo dpkg-reconfigure virtualbox-dkms

rebuild dkms modules (here is `virtualbox-dkms` as an example)

Add an existing sub-directory as a git submodule

Use case:

- there is a project directory with an initialized git repo inside

- there is a sub-directory with another initialized git repo inside

Goal:

add the subdirectory as a git submodule to the root project repo

Steps:

1. Add the submodule's url to .gitmodules and to .git/config with
   git submodule add --name <submodule_name> <url> <path_to_subdir>
2. Move the submodule's $GIT_DIR directory (.git in regular repositories) to .git/modules/<path> with
   git submodule absorbgitdirs <path_to_subdir>

Run a GUI app with sudo

Use pkexec as a GUI alternative for sudo.

A krusader's custom action as an examle:
pkexec env DISPLAY=$DISPLAY XAUTHORITY=$XAUTHORITY /bin/bash -c "cryptsetup open --allow-discards /dev/sdb7 data -d /key && mount /dev/mapper/data /media/user/data"; %aGoto("/media/user")%

Clear systemd journal

examples are taken here

Systemd stores its logs in /var/log/journal.

$ du -hs /var/log/journal/
4.1G    /var/log/journal/

Check the oldest logs date:

$ ls -lath /var/log/journal/*/ | tail -n 2
-rw-r-x---+ 1 root systemd-journal 8.0M Dec 24 05:15 user-xxx.journal

Clear by date: older than X days

Clearing everything older than 10 days:

$ journalctl --vacuum-time=10d
...
Vacuuming done, freed 2.3G of archived journals on disk.

Clear by size: if they exceed X storage

Clearing everything that exceeds 2GB size:

$ journalctl --vacuum-size=2G
...
Vacuuming done, freed 720.0M of archived journals on disk.