Unsorted Notes

Great Flamingo

GitHub

URLs:

  • Add ?w=1 in a pull request to ignore whitespace changes
  • Add .patch to a pull request to get the change as an unified diff
  • In a message, <details> ... </details> creates a drop-down

Markdown:

  • <details> can be used for long fold/unfold list, traceback, etc.

Git

Remove latest commit

git reset --hard HEAD~1

List tags containing a specific commit

$ git tag --contains 94a3b83f9f1fd52a78b9d49b32ddfae40182f852
12.0.0.0b1
12.0.0a0
2014.2
2014.2.1
...

Remote branches

  • List remote branches: git branch -r

  • Create a new branch fix_1369426_icehouse tracking the remote branch origin/stable/icehouse:

    git branch --track fix_1369426_icehouse origin/stable/icehouse

  • (Track and) Pull a remote branch:

    git branch --track NAME_REMOTE_BRANCH
git fetch --all   # or: git pull --all

Shell script

  • bash8: A pep8 equivalent for bash scripts

  • checkbashisms: static analysis tool for shell scripts. It looks for particular patterns which indicate a script might be relying on /bin/sh being bash.

  • shellcheck: static analysis and linting tool for sh/bash scripts

  • $'...' interprets escape sequences (like \n) in '...'

  • <<<"HELLO" syntax, known as “here-string”, creates a temporary file which contains the string HELLO and uses this file as the child process stdin (fd 0).

  • "$(...)" syntax allows to pass the output of a command to a program with newline characters:

    python3 -c "$(echo -e "for i in range(3):\n  print(i)")"

Example:

haypo@selma$ echo $'a\rb'|hexdump -C
00000000  61 0d 62 0a                                       |a.b.|
00000004
  • sh is supposed to be the minimalist shell (faster, but less feature)
  • bash has more feature and is quite common, but not available by default on FreeBSD for example.
  • dash is a minimalist shell used as ‘sh’ on Debian

Test:

  • [ is a program: /usr/bin/[ on Linux
  • man test
  • man [ # sometimes display bash manual page
  • [[ … ]] is a bash built-in, so specific to bash

Replace name.py string with name, remove .py suffix:

script="name.py"
# display "name"
echo ${script:0:-3}

Misc:

Operating systems

macOS (Mac OS X) versions:

macOS Name Darwin Version Release Year
macOS 10.13 High Sierra 17.x 2017 (June)
macOS 10.12 Sierra 16.x 2016
macOS 10.11 El Capitan 15.x 2015
macOS 10.10 Yosemite 14.x 2014
macOS 10.9 Mavericks 13.x 2013
macOS 10.8 Mountain Lion 12.x 2012
macOS 10.7 Lion 11.x 2010
macOS 10.6 Snow Leopard 10.x 2008
macOS 10.5 Leopard 9.x 2006
macOS 10.4 Tiger 8.x 2004

Use sw_vers in the command line to get macOS version.

  • Ubuntu releases:
    • 16.10: Yakkety Yak (not released yet, scheduled for 2016-10-20)
    • 16.04 LTS: Xenial Xerus, 2016-04-21
    • 15.10: Wily Werewolf, 2015-10-22
    • 15.04: Vivid, 2015-04
    • 14.10: Utopic, 2014-10
    • 14.04 LTS: Trusty, 2014-04
    • 12.04 LTS: Precise, 2012-04
  • Fedora releases:
    • Fedora 24: 2016-06-21
    • Fedora 23: 2015-11-03
    • Fedora 22: 2015-05-26
    • Fedora 21: 2014-12
    • Fedora 20: 2013-12, Heisenbug
    • Fedora 19: 2013-07, Schrödinger’s Cat
  • Debian releases:
    • Debian 9 “Stretch”: June 17th, 2017
    • Debian 8 “Jessie”: April 26th, 2015

FreeBSD releases, and Unsupported FreeBSD Releases:

FreeBSD Release End of life
FreeBSD 11.0 2016-10 2021-09-30
FreeBSD 10.0 2014-01 2018-10-31
FreeBSD 9.0 2012-01 2016-12
FreeBSD 8.1 2010-07 2012-07
FreeBSD 7.0 2008-02 2009-04
FreeBSD 6.2 2007-01 2008-05

Microsoft Windows versions (version numbers):

Windows Version Release End of mainstream support Extended support
Windows 10 10.0 2015-07 2020-10 2025-10
Windows 8.1 6.3 2013-10 2018-01 2023-01
Windows 8 6.2 2012-10 2016-01 2016-01
Windows 7 6.1 2009-10 2015-01 2020-01
Windows Vista 6.0 2007-01 2012-04 2017-04
Windows XP Professional x64 5.2 2005-04 2009-04 2014-04
Windows XP 5.1 2001-10 2009-04 2014-04

Note

For applications that have been manifested for Windows 8.1 or Windows 10. Applications not manifested for Windows 8.1 or Windows 10 will return the Windows 8 OS version value (6.2). To manifest your applications for Windows 8.1 or Windows 10, refer to Targeting your application for Windows.

Gnome-Terminal

Configure Gnome-Terminal to select a full URL double-click:

dconf write /org/gnome/terminal/legacy/profiles:/:${Profile_ID}/word-char-exceptions '@ms "-,.;/?%&#_=+@~·:"'

Replace ${Profile_ID} with the profile identifier. To get it:

$ gsettings get org.gnome.Terminal.ProfilesList list
['b1dcc9dd-5262-4d8d-a863-c897e6d979b9']

Example:

dconf write /org/gnome/terminal/legacy/profiles:/:b1dcc9dd-5262-4d8d-a863-c897e6d979b9/word-char-exceptions '@ms "-,.;/?%&#_=+@~·:"'

To see notifications on irssi, use XTerm color theme, rather than the default “Tango” theme: XTerm theme has a better contrast.

Android

Avoid music applications (Spotify, radio) to stop when idle (phone locked):

  • Parameters > Network > Save data > select application: allow your music applications
  • Parameters > Batterie > Applications: allow your music applications

IRC

Give operator and owner permission to mdk:

/msg chanserv FLAGS #python-fr mdk +AFRefiorstv

Kick a spammer with a link to AFPy charter:

/msg ChanServ AKICK #python-fr ADD spammer_nickname !T 1h https://www.afpy.org/docs/charte

List operators of channel:

/msg ChanServ access #python-fr list

#python-dev flags to prevent people who are not logged in to an account from talking:

/mode #python-dev -q $~a

SSH keygen

Create an SSH key:

ssh-keygen -t ed25519 -o -a 100 -C "haypo2017" -f ssh_key
  • -t: key type, http://ed25519.cr.yp.to/
  • -a 100: use 100 rounds of the key derivation function for the passphrase, increase resistance to brute-force password cracking
  • -C: comment
  • -f: filename
  • -o: save private keys using the new OpenSSH format, increased resistance to brute-force password cracking (in fact, -t ed25519 already enables this option)

Issues with ed25519:

Links:

SSH agent:

  • Modify /etc/pam.d/* to lines containing “pam_gnome_keyring.so”
  • Make sure that login still works after the change!!!

Gnome and SSH passphrase:

sudo dnf install -y openssh-askpass

tmux

  • tmux attach
  • tmux ls
  • CTRL+b …
    • [: navigation (scroll), ‘q’ to quit navigation mode
    • d: detach
    • c: new window
    • n / p: next/previous window
    • :: open the command line (“prompt”)
    • ,: name the window
    • w: window list
    • &: kill the window
  • Command line or “prompt” (opened by CTRL+b :):
    • list-sessions
  • tmux shortcuts & cheatsheet

Rounding

Wikipedia: https://en.wikipedia.org/wiki/Rounding

Rounding modes for floating point numbers:

  • ROUND_FLOOR: Round towards minus infinity (-inf).
    • C: floor()
    • Python: math.floor(float)
    • Python: math.floor(-0.1) == -1
    • Python: math.floor(0.9) == 0
    • For example, used to read a clock.
  • ROUND_CEILING: Round towards infinity (+inf).
    • Python: math.ceil(float)
    • Python: math.ceil(0.1) == 1
    • Python: math.ceil(-0.1) == 0
  • ROUND_HALF_EVEN: Round to nearest with ties going to nearest even integer.
    • For example, used to round from a Python float.
    • Python: round(float)
    • Python: round(0.5) == 0
    • Python: round(1.5) == 2
    • Python: round(2.5) == 2
    • This is the default rounding mode used in IEEE 754 floating-point operations.
  • ROUND_UP: Round away from zero.
    • For example, used for timeout. ROUND_CEILING rounds -1e-9 to 0 milliseconds which causes bpo-31786 issue. ROUND_UP rounds -1e-9 to -1 millisecond which keeps the timeout sign as expected. select.poll(timeout) must block for negative values.
  • ROUND_DOWN: Round towards zero.
    • C: (int)double, ex: (int)0.9 == 0
    • Python: int(float)
    • Python: int(0.9) == 0
    • Python: int(-0.9) == 0
    • Python: float.__trunc__()

Other rounding modes (ex: Python decimal module):

  • ROUND_HALF_DOWN: Round to nearest with ties going towards zero.
  • ROUND_HALF_UP: Round to nearest with ties going away from zero.
  • ROUND_05UP: Round away from zero if last digit after rounding towards zero would have been 0 or 5; otherwise round towards zero.

IEEE 754 defines 4 modes:

  • ROUND_HALF_EVEN: default mode
  • ROUND_FLOOR
  • ROUND_CEILING
  • ROUND_DOWN

Links:

Linux: follow process execution

wget mirror

Download a “Index of” Apache listing and subdirectories, but not parents.

wget –mirror –no-parent -e robots=off URL

robots=off is needed to downloda OpenStack CI logs, since the robots.txt disallow everything.

dd

Write a raw image to a USB key:

lsblk # check if the USB key is connected
sudo dd if=bios.img of=/dev/disk/by-id/usb-LEXAR_JUMPDRIVE_0A4F1007191812160305-0\:0 status=progress oflag=direct

ssh-agent

List keys of ssh-agent:

ssh-add -l

Add a key:

ssh-add ~/.ssh/id_rsa

Remove all keys:

ssh-add -D

KDE Connect on Fedora

Commands:

sudo dnf install kde-connect-nautilus
sudo firewall-cmd --zone=public --permanent --add-port=1714-1764/tcp
sudo firewall-cmd --zone=public --permanent --add-port=1714-1764/udp
sudo systemctl restart firewalld.service

See also https://community.kde.org/KDEConnect

SELinux

Display SELinux alerts in Gnome: sealert.

Dummy command to restore SELinux labels on the whole operating system:

restorecon -Rv /

/etc/selinux/config config file:

SELINUX=enforcing
SELINUXTYPE=targeted

Check current SELinux config:

$ getenforce
Enforcing

Valgrind

Search for memory leak: malloc() not followed by free(), limit the call stack to 20 frames:

PYTHONMALLOC=malloc valgrind --leak-check=full --show-leak-kinds=all --log-file=valgrind.log --num-callers=20 ./python script.py

Valgrind with gdb server to inspect a bug in gdb:

# First terminal
valgrind --vgdb=yes --vgdb-error=0 program [arg1 arg2 ...]

# Second terminal
gdb
# then type in gdb:
# (gdb) target remote | vgdb

Generate a suppression for a false alarm:

--gen-suppressions=yes

Python issues related to Valgrind:

Floating point number

Binary IEEE 754:

Other:

  • GMP: free library for arbitrary precision arithmetic, operating on signed integers, rational numbers, and floating-point numbers.
  • MPFR: multiple-precision floating-point computations with correct rounding. MPFR is based on the GMP multiple-precision library.
  • MPFI: multiple precision interval arithmetic library based on MPFR

Mplayer

Increase maxiumum volume:

mplayer -softvol -softvol-max 300 video.avi

Virtualization: run an AArch64 VM on x86-64

Before starting virt-manager, install (edk2-aarch64 is for UEFI):

sudo dnf install qemu-system-aarch64 edk2-aarch64

In virt-manager, pick “arch: AArch64” in the first dialog of the wizard.

Coredump Linux

Default configuration:

$ cat /proc/sys/kernel/core_pattern
|/usr/lib/systemd/systemd-coredump %P %u %g %s %t %c %h

Create coredump file in the current directory:

sudo bash -c 'echo "%e.%p.core" > /proc/sys/kernel/core_pattern'

Create coredump filename like python-123.core.

Maximum core dump size:

$ ulimit -c
unlimited

Test:

$ ./python -c 'import ctypes; ctypes.string_at(0)'
Segmentation fault (core dumped)
$ ls *.core
python.347656.core

See also man core.

Firefox

about:config:

Enter namespace filesystem of a Flatpak application or container

If a Flatpak application is the pid 76688, inspect the process with:

  • /proc/76688/root/ : Filesystem of the process.
  • /proc/76688/mountinfo : Mount informations
  • /proc/76688/ns/mnt : points to “mnt:[4026533594]”

For example, in a Flatpak application, the first line of mountinfo is something like “(…) /newroot / rw,nosuid,nodev,relatime - tmpfs tmpfs (…)” which means that the whole operating system is in memory, not on disk. Only following mounts can map to directories on the machine disk.

See also the nsenter command, and ip netns help for network namespaces.

Debian

  • List files contained in a package: dpkg --listfiles python3.9-dev.
  • Search which package contains a file: dpkg -S /path/to/file.

Dev Cython

Run a single test of the Cython test suite:

python runtests.py '.*test_unicode.*' -vv

Compile file.pyx to file.c:

python -m cython file.pyx

or:

cython file.pyx

Compile file.pyx to file.c and builds a dynamic library (C extension):

cythonize -i file.pyx

Documentation: Source Files and Compilation

Video for Linux (V4L): control your webcam

  • GUI: gtk-v4l
  • CLI: v4l2-ctl --list-devices

LVM

Hierarchy:

  • Disks and disk partitions (primary/secondary)
    • lsblk
    • parted /dev/vda
    • (parted) Extend the second partition: resizepart 2 100%
  • LVM Physical Volume (PV)
    • pvs
    • pvscan
    • Extend a PV: pvresize /dev/vda2
  • LVM Volume Group (VG)
    • vgdisplay
    • vgs
    • vgscan
  • LVM Logical Volume (LV)
    • lvscan
    • Add 6 GB to /root: lvextend -L +6G /dev/vg_root_python-builder-rhel7.osci.io/root
    • Add all free space to /home: lvextend -l +100%FREE /dev/vg_root_python-builder-rhel7.osci.io/home
  • Filesystem (ext4, XFS, btrfs, etc.)
    • df -h
    • Resize /root to its LV: resize2fs /dev/mapper/vg_root_python--builder--rhel7.osci.io-root
    • Resize /home to its LV: resize2fs /dev/mapper/vg_root_python--builder--rhel7.osci.io-home

C++ language

__cplusplus macro:

  • C++98: 199711
  • C++11: 201103
  • C++14: 201402
  • C++17: 201500

Hardware bugs