things-I-use-but-keep-forgetting

Organized cheatsheet of commands I use but keep forgetting.

Development

Linux

Journalctl

Logs from last boot session in reverse order

journalctl -rb -1

User sessions

Where are things autostarted for new user sessions:

Freedesktop specifications:

/etc/xdg/autostart/thing.desktop
~/.config/autostart/thing.desktop

Systemd (more info):

• Global definitions of user sessions (by root):

/etc/systemd/user/default.target.wants/* → /usr/lib/systemd/user/thing.service

Manage with:

systemctl --user --global disable thing.service
systemctl --user --global enable thing.service

• User defining its own session:

~/.config/systemd/user/default.target.wants/*.service → ~/.local/share/systemd/user/thing.service

Manage with:

systemctl --user status thing.service
systemctl --user edit thing.service
systemctl --user enable thing.service
systemctl --user restart thing.service
journalctl --user
systemd-analyze --user security thing.service

Terminal configuration

TTY font size

dpkg-reconfigure console-setup
# Choose font 'Terminus', 'fixed' has less available sizes
# Select bigger font size, it will need framebuffer available

Ctrl+Alt+Backspace in X

In /etc/default/keyboard

XKBOPTIONS="terminate:ctrl_alt_bksp"

Debian

Add PPA to debian

add-apt-repository ppa:yuezk/globalprotect-openconnect

Add a key with apt-key

Newer solution: https://wiki.debian.org/DebianRepository/UseThirdParty

Deprecated:

apt-key adv --keyserver keyserver.ubuntu.com --recv-keys XXXXXXXXXXX
apt-key adv --fetch-keys https://packages.cloud.google.com/apt/doc/apt-key.gpg

Migrate old APT keys

# Find keys, note the last 8 chars of the cert to be migrated
apt-key list
# Export the cert
apt-key export 87654321 | gpg --dearmour -o /etc/apt/trusted.gpg.d/my.gpg
# Modify repo file
deb [arch=amd64 signed-by=/etc/apt/trusted.gpg.d/my.gpg] https://my.repo/debian testing main
# Delete key
apt-key del 87654321

Reset aptitude status

rm -f /var/lib/aptitude/pkgstates*

Remove dangling configurations from uninstalled packages.

aptitude purge ?config-files

With dpkg only

dpkg --purge $(dpkg --get-selections | grep deinstall | cut -f1)

Enable weekly fstrim

systemctl enable fstrim.timer

Change default Java version

update-alternatives --config java

Apt pinning

With testing and unstable repositories, prefer testing packages. In /etc/apt/preferences.d/

Package: *
Pin: release a=testing
Pin-Priority: 800

Also prefer the firefox package from unstable

Package: firefox
Pin: release a=unstable
Pin-Priority: 999

Vim

Search and replace

:%s/search/replace/g

Ctags support

apt install exhuberant-ctags
cd repos/my_project
ctags -R -f .tags .

Launch vim and test looking for a function definition with Ctrl+], return to the previous position with Ctrl+t

Bash

Configuration files

https://www.gnu.org/software/bash/manual/html_node/Bash-Startup-Files.html

Interactive login shells

/etc/profile
~/.bash_profile
~/.bash_login
~/.profile

Interactive non-login shells

/etc/bash.bashrc
~/.bashrc

Since ~/.bash_profile usually loads ~/.bashrc, set there stuff for every shell

Non-interactive

Sometimes interactive contents of .bashrc may block session scripts. To avoid this, have the interactive parts after this line:

[ -z "$PS1" ] && return

Curl

Fixed SSL version

curl --tls-max 1.2 --tlsv1.2

Openssl

Verify SSL negotiation

openssl s_client -starttls smtp -crlf -connect smtp.office365.com:587

SSL negotiation without SNI

openssl s_client -noservername -connect host:port

Docker

Inspect image content, avoid layer separation

docker create --name=YOLO image:tag
docker export YOLO | tar t
docker rm YOLO

Kubernetes

Contexts

kubectl config current-context
kubectl config get-contexts
kubectl config use-context yolo
kubectl config set-context --current --namespace=yolo-namespace

Hardware

Great list of hardware details: inxi

inxi -Fxz

List of available soundcards

cat /proc/asound/cards

Readable tree with every USB device

lsusb -tv

List all pulseaudio modules running

pactl list modules