Using Linux

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find ~/.mozilla/firefox -name "cookies.sqlite" -exec sqlite3 {} "SELECT * FROM moz_cookies;" \;

sudo apt remove ungoogled-chromium
sudo apt remove ungoogled-chromium-common
sudo dpkg -i ungoogled-chromium-common*.deb
sudo dpkg -i ungoogled-chromium_*.deb
rm ungoo*.deb

glxinfo | grep 'compat profile'

javascript:{
document.querySelector("[name=firstname]")[0].value="Firstname";
document.querySelector("[name=lastname]")[0].value="Lastname";
void(0)}

# https://old.reddit.com/r/firefox/comments/pv5exw/solved_crazy_amounts_of_writes_to_ssd_by_firefox/
# https://wiki.archlinux.org/title/Profile-sync-daemon
# https://wiki.archlinux.org/title/Firefox/Profile_on_RAM
# https://github.com/graysky2/profile-sync-daemon

sudo dnf install profile-sync-daemon
psd

# Add support for a couple more browsers:
sudo cp /usr/share/psd/browsers/chromium /usr/share/psd/browsers/ungoogled-chromium
sudo cp /usr/share/psd/browsers/chromium /usr/share/psd/browsers/BraveSoftware

# I haven't tried this, but probably you could do same
# for Thunderbird profiles, by copying
# /usr/share/psd/browsers/firefox and editing to make
# /usr/share/psd/browsers/thunderbird

# Following would change it to cache just Firefox:
# Edit $HOME/.config/psd/psd.conf
# Change line:
    #BROWSERS=()
# to:
    BROWSERS=(firefox)

# See what the sync-daemon will do:
psd p

# Quit all browsers.
# Make a backup of your browser profile(s).

# Start the daemon:
systemctl --user enable psd.service
systemctl --user start psd.service
systemctl --user status psd.service
psd p
ls -l $HOME/.mozilla/firefox

# Launch browser(s) again.
# Then check disk writes:
sudo iotop -ao

[Unit]
Description=Timer for Profile-sync-daemon

[Timer]
OnUnitActiveSec=
OnUnitActiveSec=10m

# https://help.ubuntu.com/lts/serverguide/postfix.html
# https://docs.fedoraproject.org/en-US/fedora/rawhide/system-administrators-guide/servers/Mail_Servers/#s3-email-mta-postfix-conf

# see if postfix is installed
apt list | grep ^postfix/
apt show postfix
less /etc/postfix/main.cf      # shouldn't need to change anything
sudo dpkg-reconfigure postfix
# if not installed:
sudo apt install postfix

sudo apt install mailutils

# see if postfix is running
sudo service postfix status
# Or:
sudo systemctl status postfix --full --lines 1000
# If not running:
sudo service postfix restart
# Or:
sudo systemctl enable postfix
sudo systemctl start postfix
cat /var/log/mail.log

# forward all mail to root account to user1 account
sudo cat /etc/aliases
# sudo edit /etc/aliases to:
postmaster:    root
root:   user1
# then
sudo newaliases
# then
sudo touch /root/.forward
# and sudo edit /root/.forward to contain
user1@localhost
# then
sudo adduser user1 mail
# Or:
sudo usermod --append -G mail user1
sudo service postfix restart
sudo systemctl restart postfix
# log out and back in

# test when logged in as user1
# note: mailbox won't exist until you send first message to it
mail -s "subject1" root </etc/group
mail -s "subject2" user1 <<< 'body of the message'
mail

# postfix: set as "internet"
sudo dpkg-reconfigure postfix

less /etc/postfix/main.cf
less /usr/share/postfix/main.cf.dist
less /etc/postfix/master.cf

cat /var/log/mail.log
# I can see it trying to send to external server, but failing

man postfix-tls
man 5 postconf
man 5 master

# In /etc/postfix/master.cf, un-comment line:
#submission inet n - n - - smtpd
# and un-comment following -o lines,
# EXCEPT for the lines containing "restrictions=$mua_",
# leave those commented-out.

https://serverfault.com/questions/1046542/how-to-enable-tls-with-port-587-with-secure-authentication-on-postfix
https://wiki.archlinux.org/title/postfix

# Got to point where mail was going out to SMTP server, and
# being rejected because sender was not using a FQDN.
# Support for SMTP server says: don't use SMTP, you'll
# be fighting the spam filters.

sudo apt install mailutils mailutils-imap4d mailutils-mda mailutils-doc

sudo systemctl status mailutils-imap4d --full --lines 1000
# FAILED

man imap4d
imap4d --config-help | less

ports TCP 143, TCP 220, UDP 220, TCP 993
https://www.tutorialspoint.com/unix_commands/imapd.htm

sudo apt install dovecot-core dovecot-imapd
sudo systemctl status dovecot --full --lines 1000

# Edit /etc/dovecot/conf.d/10-mail.conf to say:
mail_location=mbox:~/Mail:INBOX=/var/mail/%u

/etc/init.d/dovecot restart

# test that local mail works; may have to install Postfix

# Set client to use port 993.
# FAILED on Thunderbird; it wants a FQDN on email address

cat /var/log/dovecot.log

https://www.linux.com/news/how-build-local-imap-server/
https://www.redhat.com/sysadmin/install-configure-dovecot
https://www.dovecot.org/
https://docs.fedoraproject.org/en-US/fedora/rawhide/system-administrators-guide/servers/Mail_Servers/

sudo apt install pdftk
pdftk PDF_File.pdf burst # strip out all pages and creates individual .pdf files

#Sign the signature page with GIMP
#Create a new page to add new text with LibreOffice 
#Paste signature into new page and export as PDF

ls *.pdf >> pdf-filenames.txt #Create file of individual page names
value=$(<pdf-filenames2.txt) #Assign pagenames to bash variable
pdftk $value cat output Merged_Document.pdf #Merge the files back into one

sudo zypper install tidy

# None of the following modify your HTML files:

tidy -errors -quiet FILENAME.html >/dev/null
tidy -errors -quiet --mute-id yes FILENAME.html >/dev/null

tidy -errors -quiet --show-filename yes --fix-uri no --mute UNKNOWN_ENTITY,CONTENT_AFTER_BODY,REMOVED_HTML5,ILLEGAL_URI_CODEPOINT,ESCAPED_ILLEGAL_URI *.html >/dev/null 2>report.txt

for f in *.html; do echo "$f" '---------------------'; tidy -errors -quiet "$f" >/dev/null; done

youtube-dl -f mp4 -o OUTFILENAME.mp4 https://www.youtube.com/watch?v=SOMETHING
# or:
youtube-dl -x --audio-format mp3 -o OUTFILENAME.mp3 https://www.youtube.com/watch?v=SOMETHING

# Debian-style rename command; apparently Red Hat version is different.
rename 's/ //g' *
rename 's/.mp4.png/.png/' *.png
for i in *.png ; do j=`basename "$i" .png` ; echo "$j" ; convert "$i" -quality 92 "$j".jpg ; done
rename 's/png.jpg/.jpg/' *.jpg

identify -verbose FILENAME

identify -format %w FILENAME
echo $W

convert -resize "${MAXWIDTH}" OLDFILENAME NEWFILENAME

# Add 1-pixel black border to image:
convert -bordercolor black -border 1 OLDFILENAME NEWFILENAME

sudo apt install libimage-exiftool-perl

# display EXIF data using very short tag-names
exiftool -veryShort FILENAME

# remove all EXIF data from files
exiftool -all= -progress FILENAMES
rm *original
# or
exiftool -all= -progress FILENAMES | grep Error
rm *original
# or
for i in *.jpg; do echo "Processing $i"; exiftool -all= "$i"; done

# remove geotag EXIF data from files
exiftool -geotag= -progress FILENAMES
# maybe
exiftool -gps:all= -progress FILENAMES

# remove all EXIF data from files
exiv2 -q rm FILENAMES

ffmpeg -i INPUT.mp4 -c copy -ss [starting time in hh:mm:ss] -to [finish, in hh:mm:ss] OUTPUT.mp4

sudo apt install libimage-exiftool-perl
exiftool -veryShort FILENAME
exiftool -veryShort -x IngredientsFilePath -x IngredientsToPart -x IngredientsFromPart -x IngredientsDocumentID -x IngredientsMaskMarkers -x IngredientsInstanceID -x Lyrics -x Lyrics-eng -x Comment -x Comment-eng -x Composer -x Album -x Artist -x Band -x Subtitle -x HistoryAction -x HistoryInstanceID -x HistoryWhen -x HistorySoftwareAgent FILENAME

# part of ffmpeg package
ffprobe FILENAME

# http://www.ibiblio.org/mp3info/
sudo apt install mp3info
mp3info -x -f -F FILENAME

# https://sourceforge.net/projects/mp3diags/
# http://mp3diags.sourceforge.net/
sudo apt install mp3diags
mp3diags

# Extract audio from video file:
ffprobe INPUT.mp4 2>&1 | grep 'Audio:'
ffmpeg -i INPUT.mp4 -map 0:1 -c copy OUTPUT.aac
ffmpeg -i INPUT.mp4 -vn -acodec copy OUTPUT.mp3

HISTSIZE=2000

# https://www.gnu.org/software/bash/manual/bash.html#index-HISTIGNORE
HISTIGNORE='reboot.*;shutdown.*'

# When shell exits, append to history file instead of overwriting it
shopt -s histappend

# At an empty command-line:
sudo !!   # run previous command with sudo in front
Up-arrow  # reuse previous commands
Ctrl+r    # search command history
history | grep PATTERN    # see all times you used PATTERN
for i in $(cat FILENAME.txt); do CMDNAME $i; done

# In middle of a command:
# First there is command-line editing:
Alt+.     # reuse previous command arguments
Alt+B     # move left 1 word
Alt+F     # move right 1 word (but collides with File menu)
# See "man readline".
# See "less /etc/inputrc", override in "$HOME/.inputrc".
# Then there is command completion:
Tab       # filename completion
# See "less /usr/share/bash-completion/bash_completion".
# Add more in /etc/bash_completion.d/
# See active definitions: "complete".

export PAGER="most"

# Delete 4th line from a file, changing file:
sed -i '4d' FILENAME

# Delete blank lines from a file, changing file:
sed -i '/^$/d' FILENAME

# Delete lines that start with a certain word, changing file:
sed -i '/^WORD/d' FILENAME

# Edit strings, changing file:
sed -i 's/OLD/NEW/' FILENAME

# In lines containing STR, edit strings, changing file:
sed -i '/STR/s/OLD/NEW/' FILENAME

# Change block of text across newline, not changing file:
sed '$!N;s/STARTPATT\nENDPATT/NEWTEXT1\nNEWTEXT2/;P;D' FILENAME

# Get lines that do NOT match pattern, and output to stdout:
grep -v 'PATTERN' FILENAME

# Process a group of whole lines, and output to stdout:
awk '/STARTPATTERN/,/ENDPATTERN/ { print }' FILENAME
awk '/STARTPATTERN/,/ENDPATTERN/ { gsub(/PATTERN/,"NEW"); print }' FILENAME

# Get value out of a file full of "KEY=VALUE" lines:
( . /etc/os-release && printf '%s\n' "$NAME" )

# Make lots of files:
seq 1 100 | xargs --verbose touch

# Basic shell loop:
for file in *; do wc -l "$file"; done
while true; do echo 1; sleep 5; done      # infinite loop

# Find any HTML file that does not contain an h1 tag:
grep -L '<h1' *.html

# To dump a log file into a pastebin:
wgetpaste log.txt

# Open a file using GUI app:
xdg-open FILENAME        # uses default app
mimeopen -a FILENAME     # asks what app to use

# See if a file contains any unicode chars:
diff -u FILENAME <(cat -v FILENAME)

# change terminal background color at random
# adapted from /u/code33301
q="\033]11;"
w=("#3c3c76" "#527774" "#32573d" "#800080" "#800000" "#A05000")
e="\007"
r=$((RANDOM%7))
if [ "$r" -ne "6" ]; then
	echo -ne $q${w[$r]}$e
fi
# else use default system color

sudo apt update
sudo apt install ttf-mscorefonts-installer
sudo fc-cache -f -v		# build font cache files

sudo apt install fontforge
wget https://gist.github.com/maxwelleite/10774746/raw/ttf-vista-fonts-installer.sh
chmod a+x ttf-vista-fonts-installer.sh
sudo bash -c ./ttf-vista-fonts-installer.sh
rm ttf-vista-fonts-installer.sh

fc-list             # all fonts installed in system
fc-match serif      # font you get for "serif" use
fc-match sans-serif # font you get for "sans-serif" use
fc-match monospace  # font you get for "monospace" use

for family in serif sans-serif monospace Arial Helvetica Verdana "Times New Roman" "Courier New"; do
  echo -n "$family: "
  fc-match "$family"
done

# Connect a phone, accept connection on phone screen, and then:
lsusb
lsusb -D /dev/bus/usb/BUSNUMBER/DEVICENUMBER
udevadm info /dev/bus/usb/BUSNUMBER/DEVICENUMBER
udevadm info /dev/bus/usb/BUSNUMBER/DEVICENUMBER | grep DEVLINKS
ls -l /run/user/$UID/gvfs/

man mtp-tools

systemctl status | grep mtp | grep -v grep

pamac list | grep mtp
mtpfs
mtp-detect | less

pamac info gvfs-mtp   # for GNOME/GTK file managers
pamac info kio-extras # for KDE file managers

sudo pamac install gmtp

jmtpfs --listDevices	# list MTP devices
# gmtp, gvfs, gvfsd-mtp, mtpfs ?
# https://github.com/whoozle/android-file-transfer-linux

cat /etc/*release
cat /etc/upstream-release/lsb-release
cat /etc/debian_version
cat /proc/version
lsb_release -a

echo $XDG_SESSION_TYPE
echo $XDG_CURRENT_DESKTOP
echo $SHELL

history | awk '{print $2}' | sort | uniq -c | sort -nr | head -n 10

lsof | grep i386-linux-gnu && echo "Found 32-bit library in use" || echo "No 32-bit library in use"
dpkg -l | grep "^ii" | grep ":i386" && echo "Found 32-bit packages installed" || echo "No 32-bit packages installed"

tail -n +1 /sys/devices/system/cpu/vulnerabilities/*
lscpu

wget https://cdn.arstechnica.net/wp-content/uploads/2019/10/rdrand-test.zip
unzip rdrand-test.zip
./rdrand-test/amd-rdrand-bug

sudo bash
sudo echo performance | tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor

sudo ps -ex | grep oom

sudo journalctl | grep 'Out of memory'
# To see more, take the timestamp when that occurred, and do:
sudo journalctl | grep 'TIMESTAMP'

sudo systemctl status systemd-oomd --full --lines 1000

# to turn it off, persistently across reboots:
sudo systemctl mask systemd-oomd.service

# Starting with systemd 251, unit status will show "oom-kill" if killed by OOM:
sudo systemctl status UNIT

# https://opensource.com/article/21/10/memory-stats-linux-smem
smem -c pss -P APPNAME -k -t | tail -n 1
# Doesn't work on Flatpaks.

# "There is a systemd scope for each running app named app-flatpak-$FLATPAKID-$INSTANCEID.scope"
systemctl status --user | grep firefox | grep scope # find scope name
systemctl status --user SCOPENAME   # doesn't show memory use
systemctl show --user -p MemoryAccounting SCOPENAME # says MemoryAccounting is on
systemctl show --user -p MemoryCurrent SCOPENAME    # says "[not set]"

systemd-cgtop   # doesn't show scopes for Flatpak apps

flatpak ps
flatpak enter PROCESSID sh
# Then what ?

# Display process OOM scores, 0 == don't ever kill:
while read -r pid comm
do
    printf '%d\t%d\t%s\n' "$pid" "$(cat /proc/$pid/oom_score)" "$comm"
done < <(ps -e -o pid= -o comm=) | sort -k2 -n

# Display adjustment and score for one process:
sudo cat /proc/PROCESSID/oom_score_adj   # negative == less likely to be killed
sudo cat /proc/PROCESSID/oom_score
choom -p PROCESSID
choom -p $(pgrep firefox)

# Which processes have adjustments so less likely to kill:
export pids=""
export sep=""
for pid in `grep '-' /proc/*/oom_score_adj | cut -d / -f 3`
do
pids="$pids$sep$pid"
sep=","
done
ps -p $pids
grep '-' /proc/*/oom_score_adj

# Set a process to be harder to kill:
sudo choom -p PROCESSID --adjust -200
sudo choom -p $(pgrep firefox) --adjust -200

# Set application to be harder to kill:
for pid in `pidof APPNAME`
do
sudo echo '-200' >"/proc/$pid/oom_score_adj"
done
# Some processes seem to have hardcoded values,
# will give "permission denied".

sudo apt install vrms
# note: installation creates a monthly cron job !
vrms

Applications

Browser

Email Client

Password Manager

VPN

GUI Text Editor

CLI Text Editor

Source Code Editor

PDF Viewer and Editor

Diagram And Flowchart Editors

Genealogy (family tree)

Web Site Tools

Downloading Videos and Images

Streaming a video from computer to smart TV

Recording Desktop Activity

Recording CLI Activity

Image Viewing and Editing

Video Player

Video Editor

Audio

Encryption etc

CLI Shell

Useful CLI snippets

Office

Database

Remote Access (Remote Desktop) to Linux machine

Remote Access (SSH) to another Linux machine

Games

E-Book / epub Readers

Things To Do

Updating

Special hardware

After using Linux for a while

Miscellaneous

CLI stuff

Keyboard

Fonts

Printing

Scanning

Time service

Connect Android phone via USB cable to Linux

See what distro/kernel versions you are using

See if you are using any 32-bit software

RAM (memory) stuff

CPU stuff

CPU Performance

Processes and Threads

Swap

Out-Of-Memory (OOM)

See if you are using any non-free software

Using your Linux box to do penetration-testing of other devices

Compiling stuff from source