linux

sysctl

reduce swap usage
https://en.wikipedia.org/wiki/Swappiness

# get swappiness
cat /proc/sys/vm/swappiness
 
# set swappiness
echo "vm.swappiness = 1" > /etc/sysctl.d/90-swap.conf
 
# disable IPv6
echo "net.ipv6.conf.all.disable_ipv6 = 1" > /etc/sysctl.d/01-disable-ipv6.conf
 
# load kernel settings from all system configuration files
sysctl --system
 
# load settings from default configuration /etc/sysctl.conf
sysctl -p
 
# load settings from specified file
sysctl -p /etc/sysctl.d/filename.conf
 
# sysctl
https://www.cyberciti.biz/faq/reload-sysctl-conf-on-linux-using-sysctl/

YouTube download and convert to mp3

https://yt-dl.org/update
https://github.com/ytdl-org/youtube-dl/releases

wget -q https://github.com/ytdl-org/youtube-dl/releases/download/2019.04.30/youtube-dl -O /tmp/youtube-dl
sudo cp /tmp/youtube-dl /usr/local/sbin/
sudo chmod a+x /usr/local/sbin/youtube-dl
 
# download audio (mp3) only
youtube-dl --extract-audio --audio-format mp3 -o "%(title)s.%(ext)s" https://www.youtube.com/watch?v=foo
 
# download whole channel starting from 3 months
youtube-dl --extract-audio --audio-format mp3 -o "%(upload_date)s_%(title)s.%(ext)s" --dateafter now-3months -v https://www.youtube.com/user/OpenStackFoundation/videos
 
# update
sudo youtube-dl -U

# output template
https://github.com/ytdl-org/youtube-dl/blob/master/README.md#output-template

Install tftp server

Install tftp server package
sudo apt-get install -y xinetd tftpd tftp

Create xinetd tftp configuration

cat <<EOF> /etc/xinetd.d/tftp
service tftp
{
protocol        = udp
port            = 69
socket_type     = dgram
wait            = yes
user            = nobody
server          = /usr/sbin/in.tftpd
server_args     = /tftpboot
disable         = no
}
EOF

Create /tftpboot folder

sudo mkdir /tftpboot
sudo chmod -R 777 /tftpboot
sudo chown -R nobody /tftpboot

Restart the xinetd service

sudo service xinetd restart

Testing our tftp server

ip a add 192.168.1.1/24 dev eth0:1
echo foo > /tftpboot/testfile
tftp 192.168.1.1
get testfile
quit

Links
https://askubuntu.com/questions/201505/how-do-i-install-and-run-a-tftp-server

OpenStack: rescue / recovery system

Download rescure iso
wget http://download.grml.org/grml64-small_2018.12.iso

Create rescure system

openstack image create systemrescuecd \
  --file grml64-small_2018.12.iso \
  --disk-format iso \
  --container-format bare \
  --min-ram 512 \
  --property hw_cdrom_bus=scsi
 
# show image
openstack image list --name systemrescuecd

Attach rescure system

openstack server rescue --image systemrescuecd ${SERVER_ID}

# Login to VM console and fix issues
Detach rescure system

openstack server unrescue ${SERVER_ID}

Links
https://help.switch.ch/engines/documentation/rescue-vm/
https://grml.org/

Visual Studio Code

# deb download
# https://code.visualstudio.com/docs/setup/linux
curl https://packages.microsoft.com/keys/microsoft.asc | gpg --dearmor > microsoft.gpg
sudo install -o root -g root -m 644 microsoft.gpg /etc/apt/trusted.gpg.d/
sudo sh -c 'echo "deb [arch=amd64] https://packages.microsoft.com/repos/vscode stable main" > /etc/apt/sources.list.d/vscode.list'

sudo apt-get install apt-transport-https
sudo apt-get update
sudo apt-get install code # or code-insiders

# manual download
wget -q https://update.code.visualstudio.com/latest/linux-deb-x64/stable -O /tmp/code.deb