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Linux Common

Switch to user's shell with nologin

### This account is currently not available
sudo su -l www-data -s /bin/bash

SSH and SCP for batch mode scripts

This way it ignores password prompt (it fails) and DANGER fingerprint.

ssh -o BatchMode=yes -o PasswordAuthentication=no -o ConnectTimeout=10 -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null ... <user>@<server>
scp -q -o BatchMode=yes -o PasswordAuthentication=no -o ConnectTimeout=10 -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null <src> <dst>

SSH client config when FW dropping inactive connections

~/.ssh/config

Host *
ServerAliveInterval 20
ServerAliveCountMax 3
TCPKeepAlive no

Locale

Generate missing locales

locale-gen en_US.UTF-8

Alternatively a locale file can be created manually

localedef -i en_US -f UTF-8 en_US.UTF-8

Then setup

export LANGUAGE=en_US.UTF-8
export LANG=en_US.UTF-8
export LC_ALL=en_US.UTF-8
locale-gen en_US.UTF-8
dpkg-reconfigure locales

And / or

echo 'LANGUAGE="en_US.UTF-8"' >> /etc/default/locale
echo 'LC_ALL="en_US.UTF-8"' >> /etc/default/locale

Timezone

dpkg-reconfigure tzdata
8. Europe
39. Prague

Date and Time

date -s '2023-01-21 13:33:11'
hwclock --systohc
timedatectl

Tcpdump

tcpdump -nli eth0 -s 0 -U -w /root/tcpdump_$(date +"%d%m%Y_%H%M%S")_$(hostname).dmp host IP_ADDRESS
    ### BETTER - print ascii & data only to terminal & all to file
tcpdump -nli eth0 -A -s 0 -U -w /root/tcpdump_$(date +"%d%m%Y_%H%M%S")_$(hostname).dmp port TCP_PORT --print
  • n - don't lookup DNS names
  • l - buffered output (for tail, etc ...)
  • i - interface
  • s 0 - store whole packets (default is 68 bytes only)
  • w - store RAW packets to file instead of stdout (can be printed later using -r)
  • U - do not buffer, store packets as they arrive

For Ethereal/Wireshark in case of SSL (not PFS) in Settings > SSL protocol set in RSA key list server IP, port, ssl key and protocol http. Then use Follow TCP stream.

Start something after boot - Legacy examples

/etc/rc.local

/root/startOnBoot.sh &> /tmp/startOnBoot.log
exit 0   ### end of rc.local

Or run script with environment setup

nohup su root --shell /bin/bash --command "/root/vncserver.sh start > /tmp/vncserver.sh.log" &
exit 0   ### end of rc.local

/root/startOnBoot.sh

#!/bin/bash

### Run under user
/sbin/runuser -l jr -c 'vncserver -localhost no' &> /home/${USER}/vncserver.start.from.root
### Run under root with security limits.conf applied (probably bug)
su root --shell /bin/bash --command "/bin/stunnel /etc/stunnel/stunnel.conf"

Beware of -localhost no which setup vnc to listen on ALL interfaces.

Set HTTP proxy (environment, curl, wget)

/etc/environment

export http_proxy="http://${HOST}:${PORT}/"
export https_proxy="http://${HOST}:${PORT}"
export no_proxy="localhost,127.0.0.1,localaddress,.localdomain.com"
export HTTP_PROXY="http://${HOST}:${PORT}/"
export HTTPS_PROXY="http://${HOST}:${PORT}/"
export NO_PROXY="localhost,127.0.0.1,localaddress,.localdomain.com"

~/.curlrc

proxy=${HOST}:${PORT}
  • --noproxy '*'
  • --proxy ${HTTP_PROXY}

~/.wgetrc

use_proxy = on
https_proxy = http://${HOST}:${PORT}/
http_proxy = http://${HOST}:${PORT}/
ftp_proxy = http://${HOST}:${PORT}/

Java

export JAVA_OPTS="-Dhttps.proxyHost=${HOST} -Dhttps.proxyPort=${PORT}"
export JAVA_FLAGS="-Dhttps.proxyHost=${HOST} -Dhttps.proxyPort=${PORT}"

curl - post binary to WEB form

curl -v -F uploadBtn=Upload -F uploadedFile=@IMAGE_098.jpg https://some.domain.cz/upload.php

curl - set timeouts

CURL="/usr/bin/curl --connect-timeout 5 --max-time 10"
### Then use like
${CURL} -s -H "Content-type: application/json; charset=UTF-8" ...

Disable auto-lock, screen autolock, screensaver

apt purge light-locker

Enable auto-login

/etc/lightdm/lightdm.conf

[Seat:*]
#type=local
...
autologin-user=doma
autologin-user-timeout=5

Show information about HW, Hardware model etc

dmidecode | grep -A3 '^System Information'

Find Network Ethernet PCI ID name

grep PCI_SLOT_NAME /sys/class/net/*/device/uevent

Backup / Restore package versions

Backup current version of all installed packages

sudo apt install dpkg-dev
touch ~/installed_packages.txt
dpkg-query -l > ~/installed_packages.txt

Reinstall versions later

sudo dpkg --clear-selections
sudo dpkg --set-selections < ~/installed_packages.txt
sudo apt-get dselect-upgrade

Check 3D-Acceleration is working (HW/VM)

apt install mesa-utils nux-tools
/usr/lib/nux/unity_support_test -p   ### ALL must be yes
glxinfo -B   ### must be Device: virgl (Apple ... neco ...)

Turn OFF resising of inodes on FS

tune2fs -O ^resize_inode /dev/md0

Youtube Downloader

Download best video and audio quality
Install using pip pip3 install --upgrade youtube-dl
Or install manually youtube-dl. For merge ffmpeg or avconv are needed. Then use it like:

./youtube-dl -f bestvideo+bestaudio "URL"