Linux

Why?

Advantages

Simplicity: simple to install, simple to use -- it just works
Comfort: automatic centralized updates of ALL applications
Security: no viruses, no malware, no bloatware, no licensing worries, no waiting for important security updates
Price: it's not only free in the meaning of liberty, it's also free in the meaning of free beer
Choice: thousands of free and open source applications are available for almost every purpose, and can be automatically installed through an integrated package browser.
Community: people help and support each other, trying new things, exploring possibilities, learning technologies, and so on.
It's not THAT different from "mainstream commercial systems", but basically the same desktop environment as usual.
If you are used to one of these mainstream commercial systems, don't worry, there are many good alternatives for your favorite mainstream proprietary applications.

Handicaps

Sometimes lacking support from commercial service providers.
Sometimes difficulties with very old or very new or very exotic hardware, namely:
graphics cards, monitors, printers, tv cards.
For some excessive mainstream gaming, you might want to keep a dual-boot system.
If you are very used to a certain other system, and you don't like to learn something new, then better stay with it because there is a difference.

Findings

2014-09-10 Zum angeblichen wirtschaftlichen Erfolgsdruck von Open Source Software:
"Warum spielt man in Järrestad Fußball? Järrestad ist ein kleines Dorf in Südschweden. ...Ein sonderlich großer finanzieller Erfolg ist aber auch der Fußballverein noch nicht. Trotzdem scheint sich die Gemeinde an all diesen finanziellen Unsicherheiten wenig zu stören. Immerhin gibt es das Projekt nun schon mehr als 30 Jahre, und ans Aufhören denkt keiner. Es bleibt abzuwarten, ob sich aus dem Verein heraus vielleicht doch noch irgendein großer Verkaufserfolg entwickelt oder das Projekt wie bisher über Spenden und Sponsoren am Leben erhalten wird." -- forum.golem.de

Basics

Keys and Shortcuts

CTRL + ALT + F1-F7 - change virtual terminal; F7 is usually used by X; some distributions use F8 for boot messages
CTRL + ALT + DEL - shutdown and restart system (in virtual terminal only)
CTRL + ALT + ARROW - switch workspace to specified direction
CTRL + ALT + BACKSPACE - kill and restart X (maybe double BACKSPACE) (disabled in Ubuntu since 2008)
CTRL + ALT + D - minimize all windows, show desktop; press again to undo
CTRL + ALT + ESC - run xkill; left click to kill application, right click to cancel (XFCE only?)
ALT + F1 - open main menu
ALT + F2 - open run application dialog
ALT + F4 - close current window
ALT + F5 - unmaximize current window
ALT + F7 - move current window with arrow keys or mouse; press enter or click to finish; press ESC to cancel
ALT + F8 - resize current window with arrow keys or mouse; press enter or click to finish; press ESC to cancel
ALT + F9 - minimize current window
ALT + F10 - maximize current window
ALT + SPACE - open window menu
ALT + TAB - cycle through open applications; press shift to cycle in reverse order
ALT + PrintScreen - take a screenshot of the currently focused window
CTRL + SHIFT + ALT + ARROW - move current window to another workspace in the specified direction
SHIFT + NUM - enable/disable the cursor mouse with num pad
frequent application shortcuts
F1 - help
F3 - find (next)
F10 - open application menu
SHIFT + F10 - show sub-window menu, or context menu
F11 - fullscreen
CTRL + A - select all
CTRL + C - copy
CTRL + F - find
CTRL + G - find next
CTRL + H - replace
CTRL + K - search bar (in Firefox)
CTRL + L - location bar, goto line
CTRL + N - new window
CTRL + O - open
CTRL + P - print
CTRL + Q - quit application
CTRL + R - reload
CTRL + S - save
CTRL + T - new tab
CTRL + V - paste
CTRL + W - close tab
CTRL + X - cut
CTRL + Y - redo
CTRL + Z - undo
CTRL + + - zoom in
CTRL + - - zoom out
help.ubuntu.com/community/KeyboardShortcuts
Top 15 Shortcut Keys in GNOME and Nautilus
Extensive List of Keyboard Shortcuts for Ubuntu/GNOME Desktop

Shell

user@host:~$ - denotes a user shell.
root@host:/# - denotes a root shell.
CTRL + C - cancel the running process
CTRL + D - logout, quit current shell, end-of-file
CTRL + J - cancel search in command history, retrieve current selection
CTRL + L - clear screen
CTRL + Q - continue output to command window (after CTRL + S)
CTRL + R - search in command history (use selected with CTRL + J, cancel with CTRL + G)
CTRL + S - stop output to command window (continue with CTRL + Q)
CTRL + U - remove entry from command history
CTRL + Z - send current process to background - "zombie" - continue with fg
TAB - auto completion: continues current word if possible. If there is more than one possibility, press TAB again to get a list.
!! - repeat last command
sudo !! - repeat last command as super user
^abc^xyz - replace first occurence of abc with xyz in last command and execute this
<command> - run command in search path
./<command> - run comamand in current directory (separate shell)
. <command> - run command within existing shell -- see source -- (like #include in C).
<command1> ; <command2> - run commands one after another, without condition
<command1> && <command2> - run command 2 only if command 1 returned 0 (true)
<command1> || <command2> - run command 2 only if command 1 returned 1 (false)
<command> > [file] - redirect standard output to file. (overwrite)
<command> >> [file] - redirect standard output to file. (append)
<command> < [file] - redirect standard input from file.
<command1> | <command2> - pipe: redirect stdout of cmd1 to stdin of cmd2
<command> 2>&1 - redirect output from stderr to stdout.
<command> | tee [file] - fork output to stdout AND to file.
<command> & - run command in background.
<< x - here-doc, terminated by x (any freely defined word)
<<- - here-doc that ignores leading tabs
<<< "..." - here-string, terminated by quotation marks (single or double) or line break (?)
exec - redirect standard output or input
grep [pattern] [file] - print lines matching a pattern. Examples:
find . | grep foo
grep -e "^(WW)" -e "^(EE)" /var/log/Xorg.0.log - prints all lines that contain warnings or errors
grep -c '[;{]' *.java - quick & dirty lines-of-code (LOC) counter (more like number-of-statements)
grep -rnw --exclude-dir={boot,dev,lib,media,mnt,proc,root,run,sys,/tmp,tmpfs,var} '/' -e 'foo' - exclude system directories (see AskUbuntu #1005437)
man [command] - show manual for command. Press q to quit, h for help.
man -k [keyword] - search for keyword in all installed man pages.
Categories:
(1) - Executable programs or shell commands
(2) - System calls (functions provided by the kernel)
(3) - Library calls (functions within program libraries)
(4) - Special files (usually found in /dev)
(5) - File formats and conventions eg /etc/passwd
(6) - Games
(7) - Miscellaneous (including macro packages and conventions)
(8) - System administration commands (usually only for root)
(9) - Kernel routines [Non standard]
Ubuntu Manpage Repository
whatis - search the whatis database for complete words; the whatis database contains short descriptions of system commands.
apropos - search the whatis database for strings.
history - list last used command lines.
clear - clear current terminal.
reset - reset current terminal.
su - switch user. Commonly used to change to super user permissions.
sudo [command] - run command as super user using own credentials; similar to su -c.
sudo -b [command] - run in background (appending & would hide the auth request)
sudo -k - reset temporarily stored password (e.g. 15 min)
sudo -v - refresh temporarily stored password, ask if necessary
sudo -l - list all sudoers entries for current user
nohup [command] - continue after logout.
at 23:59 < jobs.txt - run commands in input file at certain time.
atq - list pending jobs
atrm [id] - remove a pending job
Frequently used command line options:
-a - all, archive
-c - command, checksum
-C - compress
-f - force
-h - help, human
-i - case insensitive
-l - long
-o - option, output
-p - preserve
-q - quiet
-R - recursive
-u - user, update
-v - verbose
-V - version
-z - compress
--help - long help
Variables:
printenv - prints all environment variables
export variable=wert - set
unset variable - unset
X=Y program - use program with variable X (even works as "time X=Y program")
"Unfortunately, there is no way to export variables back to the parent process, to the process that called or invoked the script or shell."
... but: see ". command" or "source" above ... (?)
avoid duplicates in bash_history: HISTCONTROL=ignoreboth:erasedups (but only avoid consecutive duplicates)
remove idea 1: awk '!x[$0]++' ~/.bash_history > ~/.bash_history.tmp && mv -f ~/.bash_history.tmp ~/.bash_history
remove idea 2: tac ~/.bash_history | awk '!x[$0]++' | tac > ~/.bash_history.tmp && mv -f ~/.bash_history.tmp ~/.bash_history - may be put into .bashrc
remove idea 3: nl ~/.bash_history | sort -k2 -k 1,1nr | uniq -f 1 | sort -n | cut -f2 > ~/.bash_history-cleaned - see How can I remove duplicates in my .bash_history, preserving order?
more: Unix shell, Unix utilities, Advanced Bash-Scripting Guide, Learning the Shell, Bash Pitfalls, Shell-Programmierung (de), Die GNU-Shell Bash (de), Bash-Befehle und Bash-Programmierung (de), Treffpunkt für Linux-Shelluser, An A-Z Index of the Bash command line for Linux, Shell/Befehlsübersicht, Shell Scripting Tutorial

Files and Streams

file [file] - print info about file's content.
less [file] - view a file. Press q to quit, h for help. '/word' searches forward, '?word' backward, n continues.
most [file] - view a file in hex mode.
head [file] - view first 10 lines of a file. Press q to quit.
tail [file] - view last 10 lines of a file. Press q to quit. Options: f: follow.
nano [file] - edit a file. Press CTRL-X to quit.
ls - list directory contents. Options: a: all, l: long.
pwd - print name of working (current) directory.
find ... - search for files or directories. Examples:
find /tmp -size +5k -iname *.html
find /etc -type f -exec grep -q searchstring {} \; -print
find ~ -mtime 2 (find all files in the user's home that have been modified within the last 2 days)
find ~ -type f -print0 | sudo xargs -0 grep -HinT "regex" - find all files whose content matches regex ignoring case, listing file names with line numbers, TAB-formatted
find /foo -xdev -samefile /foo/reference/file -printf '%i %n %p\n' - find hardlinks to a file
slocate [file] - search file systems without displaying unauthorized files.
cd [directory] - change working directory. Special: / root, ~ home, . current, .. parent, - last.
rm [file or directory] - remove file. Options: f: force, R: recursive.
shred [file] - overwrite file content. Options: u: remove, z: zero.
mkdir [directory] - make directory.
rmdir [directory] - remove empty directory.
cp [source] [target] - copy files or directories. Options: p: preserve, R: recursive.
mv [source] [target] - move (rename) files or directories.
ln -s [source] [target] - make symbolic links between files or directories.
touch [file] - create file, or update timestamp.
split - split a file into pieces.
sort - sort lines of text files.
cmp - compare files byte by byte.
diff - compare files line by line. Example:
diff -y --suppress-common-lines A.txt B.txt - compare in two colums, show differences only
comm - compare sorted files line by line. Example:
comm -3 A.txt B.txt - show differences in two columns
meld - compare files line by line in a GUI.
md5sum - compare files using MD5 sums.
sed 's/foo/bar/g' [file] - replaces all occurrences of foo with bar in file. (sed = stream edit)
chmod [options] [file] - change access permissions. Example: chmod -R ugo+x mydir.
Permissions: u user, g group, o owner, a all -- r read, w write, x execute -- s setuid (execute root's file as user)
chown [user[:group]] [file] - change file owner and group. Example: chown -R myself:mygroup mydir.
cat [file] - concatenate files and print on the standard output.
dd - convert and copy a data stream.
dd if=/dev/cdrom of=disk.iso bs=1024 - create an ISO image from a CD.
dd if=floppy.img of=/def/fd0 - copy image to floppy.
dd if=/dev/urandom of=/dev/sdb1 bs=1M count=2 - copy 2 MB random data to a partition to hide future encryption keys there.
# killall -USR1 dd - let a running dd process print its status.
hd - (= hexdump) filter files or streams to show a view like a hex editor
wc [file] - print newline, word, and byte counts.
df -hT - report filesystem disk space usage.
du -chs [directory] - report file space usage.
rsync -a /home/mydata/ /backups/data-20080810/ - file synchronization. Examples:
remote: rsync -a /home/mydata/ 192.168.1.1::mybackups/data-20080810/
over ssh: rsync -a -e ssh 192.168.1.1:/backups/data-20080810/ /home/mydata/
big files: rsync -a --partial --inplace /home/bigfiles/ 192.168.1.1::mybackups/bigfiles/
nice introduction: System Rescue CD Manual
# tar -cvzf backup-etc.tar.gz /etc/ - create backup of etc directory
$ tar -tvzf backup-etc.tar.gz - list contents of archive
# tar -xvpf backup-etc.tar.gz - decompress the backup (to preserve permissions and owner, you might need sudo!)

System

ps -efly - list current processes.
top - display tasks. k: kill, q: quit, r: renive, 1: SMP view.
taskset - retrieve or set a process's CPU affinity. Examples:
taskset -cp 0 1234 - bind process 1234 to cpu 0
taskset -c 1 [command] - launch new program on cpu 1
jobs - list background processes.
fg [job id] - run jobs in the foreground - move a background process into the foreground.
nice [command] - run with modified scheduling priority.
renice [priority] [process id] - re-set the priority of a process.
free - display amount of free and used memory in the system.
uptime - display how long the system has been running.
uname -a - print kernel information.
date - print or set the system date and time.
cal - print this month's calendar.
time [command] - print how long command takes to complete.
dmesg | less - display last kernel boot messages.
lshal - list all ? devices.
lspci - list all pci devices.
lspci -nnvv - show IDs and name, be very verbose
lsusb - list all usb devices.
whereis [command] - locate the binary, source, and manual page files for a command.
which [command] - show complete path of the executable.
pidof [process] - print the process id of a running program; may be a space-separated list of numbers.
kill [process id] - send TERM signal to the process. kill -9 [pid] sends KILL signal.
killall [name] - send TERM signal to all processes that run the specified (command) name.
exit - quit current shell.
rcconf - control services. (requires installation rcconf package)
runlevel - print previous and current runlevel; N means no previous runlevel.
shutdown [options] now - shut system down. Options: r: reboot, h: halt (poweroff), f: skip fsck.
halt/poweroff/reboot - instantly halt/poweroff/reboot the system using shutdown.
init [0123456] - change runlevel. Debian/Ubuntu: 0 halt, 1 single, 2 multi (default), 6 reboot. (prefer shutdown)
startx - initialize an X session.
/etc/init.d/gdm [start|stop|restart] - start|stop|restart X server.
# pm-hibernate - go to hibernate instantly
watch -n 1 acpi -V - watch ACPI status.
How do I change the I/O scheduler for a particular hard disk without rebooting my Linux server system?

Debian Package Management

dpkg -i file.deb - installs a package
dpkg -r file.deb - removes a package
dpkg -P file.deb - purges a package
dpkg --info file.deb - print package information such as description, version etc.
dpkg -l - lists all installed packages
dpkg -l abc* - lists all installed packages that start with 'abc'
dpkg-query -W -f='${Package}\n' - list all installed packages, only name
dpkg -s package | grep 'Status' - find out if package is installed or not
dpkg -p package - print details of available version
dpkg --get-selections > selections.txt - backup package list; * also lists removed packages
dpkg --get-selections abc - output only if package abc installed
dpkg --admindir=/media/disk-1/var/lib/dpkg --get-selections - save list of packages from other disk
dpkg --set-selections < selections.txt - restore selection state
apt-get dselect-upgrade - apply the changes set via dpkg --set-selections
echo mutt hold | dpkg --set-selections - prevents updating of 'mutt'
dpkg -S /bin/sh - shows package that a file belongs to
dpkg -L mypackage - shows files that belong to mypackage
dpkg -c file.deb - shows files that would be installed by file.deb (i.e. contents of file.deb)
dpkg --contents file.deb - list files provided (or owned) by the package (no matter if installed or not)
dpkg --configure -a - configure all packages that are unconfigured (helps after disrupted update)
dpkg-reconfigure mypackage - re-run configuration for a package
dpkg-reconfigure keyboard-configuration
apt-get update - fetch package lists from package sources (listed in /etc/apt/sources.list)
apt-get install mypackage - installs a package
apt-get remove mypackage - removes a package (keep configuration); --purge removes configuration
apt-get install evolution mutt- - installs evolution, removes mutt
apt-get upgrade - updates installed packages, doesn't add or remove packages
apt-get dist-upgrade - updates installed packages, adds or removes packages if required
apt-get clean - cleans package cache in /var/cache/apt/archives
apt-get autoclean - deletes only outdated packages from cache
apt-cache search browser - searches for 'browser'
apt-cache show mypackage - shows info for a package
apt-cache depends mypackage - display dependencies for mypackage
apt-file search stdio.h - shows package that contains a file, even if not installed yet (uses own cache that is updated with apt-file update)

User

id - print user identity.
whoami - print effective user id. Same as id -un.
who - show who is logged on.
w - show who is logged on and what they are doing.
finger [user] - display information about user.
fuser - identify processes using files or sockets.
fuser -n tcp 2001 - check if some process is using tcp port 2001
wall - sends a message to all users that are currently logged in.
useradd -m [login] - create new user and home directory.
userdel -r [login] - delete user and home directory.
passwd - change user password.

Network

ifconfig - interface configuration. Example:
sudo ifconfig eth0 192.168.1.2 netmask 255.255.255.0 - set address and subnet on eth0
netstat - show network status. Options: i: statistics, nr: routing, ta: tcp connections.
sudo netstat -tulpn - check open ports
ping [host] - ping.
traceroute [host] - traceroute.
route - show/manipulate the IP routing table. Example:
route add default gw [ip] - add default gateway (e.g. internet access router)
nmap -p- localhost - scan for open ports on localhost.
nmap -T4 -F 127.0.0.1 - quick check the reaction of the firewall.
nc -kl [port] - netcat: open listener on port and keep open
nc -zv [host] [port] - netcat: check port (zero data), verbose (without -z it would be bidirectional cat)
whois [domain] - print whois info.
dig [domain] - print DNS info. Options: x: reverse lookup.
dhclient eth0 - request ip from dhcp server.
ssh - secure shell client (remote login).
scp - secure copy (remote file copy).
wget - non-interactive download.
smbclient -U% -L localhost - list resources
ethtool -i eth0 - shows driver and firmware version
iwconfig - wireless interface configuration
iwlist [chan|scan] - wireless channel config

Devices

parted [device] - partitioning of a device.
fsck [device] - check and repair a file system.
e2fsck [device] - check and repair an ext2/3 file system. Examples:
e2fsck -fD - removes invalid entries from directory files and rebuilds the file name tree (?)
e2label [device] - get label of ext2/3 file system. also allows to set.
tune2fs [device] - adjust tunable filesystem parameters on ext2/3 filesystems. Example:
tune2fs -c 100 -i 180 - allows 100 mounts or 180 days before next e2fsck run
tune2fs -m 1 /dev/sdf1 - reduce "preserve for priviledged processes" on ext3 from 5 to 1%
# sfill -llv /media/Empty/ - secure delete (overwrite) free space on a mounted (ext2-compatible?) partition; one pass using /dev/urandom.
badblocks [device] - search a device for bad blocks; can test and refresh backups.
mount [-t type] [device] [directory] - mount a device. Examples:
mount -t smbfs //server/share /mnt/dir -o user=Workgroup/Username:Password
mount -t davfs https://webdav.mc.gmx.net /mnt/dir
mount -o loop disk.iso /mnt/image
mount -n -o remount,ro / - remount root read-only, e.g. to test it via fsck
mount -l | grep /dev/sd - print all mounted hard disk partitions
umount [device | directory] - unmount a filesystem.
dd_rescue - copy data from one file or block device to another, don't stop on error.
dd_rescue /dev/zero /dev/sda - quick overwrite disk
sudo cat [/dev/ttyS0 | /dev/psaux | /dev/input/mice] - test serial, ps/2, resp. usb mouse (move it).
sudo hdparm -tT [device] - benchmark a hard disk drive.
cat /proc/swaps - show swap status. (Same as sudo swapon --summary but less permissions required.)
ls -l /dev/disk/by-uuid - list UUIDs.
smartctl -a [device] - show SMART status.
smartctl -A [device] - show SMART attributes.
smartctl -l selftest [device] - show test log.
smartctl -t long [device] - perform long SMART test (surface test).
eject - eject removable media (/media/cdrom)
eject -x 9 /dev/scd0 - slowdown drive to 9 (minimum to play DVD)
# blockdev --getsize64 /dev/sda - returns size of device in bytes
# lde - Linux Disk Editor, supports ext2 and msdos

Graphics

glxinfo | grep rendering - check 3D acceleration.
glxgears - check 3D acceleration (subjective).
aticonfig --initial --input=/etc/X11/xorg.conf - create initial X config file.
aticonfig --od-gettemperature --od-getclocks - show temperature and clocks of an ATI card.

Shell Programming

echo - display a line of text.
echo $variable | sed 's/$variable/foo/' - do not interpret content of single quotes.
echo $variable | sed "s/$variable/bar/" - interpret content of double quotes.
echo `command` - execute command and print the result (left single quotation mark, grave accent, U+0060) - old-style, better use $(...).
read - get input; -a assigns to array, -d set delimiter (defaults to newline), -n number of characters (instead of complete line), -p display prompt, -s silent (no echo), -t timeout
PID=`pidof dd` - store the result of the command to a variable.
{ command; command; } - run as block.
(command) - run in subshell.
test - check file types and compare values.
basename [file] [[suffix]] - strip directory and suffix from filenames.
DIR="$( cd "$( dirname "$0" )" && pwd )" - get full directory name of the script no matter where it is being called from.
$0 - name of the current command.
$1...$9,${n} - arguments, n<100.
$* - expands to all arguments of a command; "$*" expands to "$1 $2 $3 ...".
$@ - expands to all arguments of a command; "$@" expands to "$1" "$2" "$3" ...
$# - number of arguments.
if [ $# -eq 0 ]; then exit 1; fi - test for zero arguments
$- - expands to the current option flags (?)
$! - process ID of the most recently executed background (asynchronous) command.
$$ - process ID of the shell. In a () subshell, it expands to the process ID of the current shell, not the subshell.
$? - exit status of the most recently executed foreground pipeline.
$(pidof dd) - use text result of the command (here: the process id) - equal to `pidof dd`.
$((512*63)) - evaluate arithmetic expression
if [[ $temp > 1000 ]]; then ...; fi - simple condition - CAUTION: this compares lexicographically, so 5 is larger than 10
if [[ $temp -gt 1000 ]]; then ...; fi - numerical comparison: -gt, -ge, -lt, -le
while kill -USR1 $PID; do sleep 15; done - while loop example.
while [ 1 ]; do - infinite loop
while [ $COUNTER -lt 60 ]; do - conditional loop
for [start] [test] [next] [body] - for loop.
trap [command] [signals] - catches keyboard sequences, e.g. for cleanup
Specials...
- [[ ... ]] vs. [ ... ] - The first has fewer surprises and is generally safer to use. But it is not portable. See Is [[ ]] preferable over [ ] in bash scripts?
- $(...) vs. `` - Why is $(...) preferred over `...` (backticks)?

Programming

ldd - prints list of shared libraries used by an executable

Configuration

ntpdate -u ntp.ubuntu.com - get time from the web
update-alternatives --config java - select Java Virtual Machine (e.g. OpenJDK or Sun Java SE)
update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.8 40 --slave /usr/bin/g++ g++ /usr/bin/g++-4.8 -- add GCC to configuration (this is disputed) with priority 40
setxkbmap de|us - set keyboard map
export http_proxy='http://[login[:password]]@host:port' export https_proxy='http://[login[:password]]@host:port' export ftp_proxy='http://[login[:password]]@host:port' - setup proxy server, e.g. in /etc/bash.bashrc.

Software Packages

aptitude show [package name] - print install status and other info of the package

Advanved

System Info

uname -a - print system information, e.g. kernel name, kernel version, hostname
dmesg - print kernel ring buffer (bootup messages)
lsb_release -a - print distribution specific information, e.g. release number, code name, distributor
getconf GNU_LIBC_VERSION - print GLIBC version (short)
ldd --version - print GLIBC version (medium)
/lib/libc.so.6 - print GLIBC version (long)
dpkg --print-architecture - print architecture, e.g. i386 or amd64
gnome-about --gnome-version - print GNOME version, distributor, and date
kde-open --version - print KDE and Qt versions
lshw -html > hardware.html - create overview of hardware
lshw -class display - shows technical info about graphics card
hwinfo - probe for hardware
hwinfo --short - print nice overview
hwinfo --<item> - print details about one of these: all, bios, block, bluetooth, braille, bridge, camera, cdrom, chipcard, cpu, disk, dsl, dvb, fingerprint, floppy, framebuffer, gfxcard, hub, ide, isapnp, isdn, joystick, keyboard, memory, modem, monitor, mouse, netcard, network, partition, pci, pcmcia, pcmcia-ctrl, pppoe, printer, scanner, scsi, smp, sound, storage-ctrl, sys, tape, tv, usb, usb-ctrl, vbe, wlan, zip
sudo dmidecode - DMI table decoder, shows various hardware info
-s [bios-vendor|bios-version|bios-release-date| system-manufacturer|system-product-name|system-version|system-serial-number|system-uuid| baseboard-manufacturer|baseboard-product-name|baseboard-version|baseboard-serial-number|baseboard-asset-tag| chassis-manufacturer|chassis-type|chassis-version|chassis-serial-number|chassis-asset-tag| processor-family|processor-manufacturer|processor-version|processor-frequency] -t [bios|system|baseboard|chassis|processor|memory|cache|connector|slot]
cpuid - print processor details
pccardctl info - might show info for older PCMCIA cards
hardinfo - HardInfo can gather information about your system's hardware and operating system, perform benchmarks, and generate printable reports either in HTML or in plain text formats.
Systeminformationen_ermitteln
inxi ... (since trusty)

Live CPU/RAM/Swap Monitoring

echo "CPU%; MEM%; SWAP%"
while true; do
    cpu=$(top -bn1 | awk '/^%C(PU|pu)/{printf("%3.1f", 100-$8)}')
    mem=$(free -m | awk '/^(Speicher|Mem):/{printf("%3.1f", ($3+$5)/$2 * 100)}')
    swap=$(free -m | awk '/^(Auslager|Swap):/{printf("%3.1f", $3/$2 * 100)}')
    echo "$cpu; ${mem}; $swap"
    sleep 1
done

Mainboard

...

CPU

dmidecode:
	Socket Designation: Socket M2
	Family: Athlon
	Manufacturer: AMD
	Signature: Family 16, Model 4, Stepping 2
	Version: AMD Phenom(tm) II X3 720 Processor
	Voltage: 1.3 V
	External Clock: 200 MHz
	Max Speed: 3200 MHz
	Current Speed: 2800 MHz
cat /proc/cpuinfo
	vendor_id	: AuthenticAMD
	cpu family	: 16
	model		: 4
	model name	: AMD Phenom(tm) II X3 720 Processor
	stepping	: 2
	cpu MHz		: 800.000
	cache size	: 512 KB
	cpu cores	: 3

Memory

free - example:

             total       used       free     shared    buffers     cached
Mem:       4119584    3445656     673928          0     275400    1880120
-/+ buffers/cache:    1290136    2829448
Swap:      8301668          0    8301668

cat /proc/meminfo - example:

MemTotal:        4119584 kB
MemFree:          672556 kB
Buffers:          275516 kB
Cached:          1880996 kB
SwapTotal:       8301668 kB
SwapFree:        8301668 kB
...

# lshw -class memory - for each bank:

bank:0
	description:   SDRAM               DIMM 800 MHz (1.2 ns)
	product:       PC100-322S
	physical id:   0                   3
	version:       0000,63 27,00
	serial:        M3 66S3323CT0-C7A
	slot:          DIMM0/J21           A3
	size:          64MiB               2GiB
	width:                             64 bits
	clock:                             800MHz (1.2 ns)

cache:1
	description: L2 Cache (unified)
	physical id: 1
	size: 1MiB
	clock: 225MHz (4.4ns)

# dmidecode --quiet --type memory - memory controller, memory modules, physical memory array, memory devices

Graphics

...

Network

...

Storage

sudo fdisk -lu [image] - print overview of disks and partitions [or images]
cat /proc/ide/hda/cache = 1961
cat /proc/ide/hda/capacity = 40088160
cat /proc/ide/hda/media = disk
cat /proc/ide/hda/model = WDC WD205BA
sudo hdparm -i /dev/sda - print info
sudo hdparm -I /dev/sda - print more info

Devices

...

Software

uname -o - operating system: GNU/Linux
uname -s - kernel name: Linux
uname -r - kernel release: 2.6.28-19-generic
uname -v - kernel version: #61-Ubuntu SMP Wed May 26 23:35:15 UTC 2010
uname -m - machine hardware: i686
uname -n - network hostname
dpkg --print-architecture - package architecture: i386
lsb_release -ds - distribution description: Ubuntu 9.04
lsb_release -cs - distribution code: jaunty
gnome-about --gnome-version - gnome about: Version: 2.26.1\nDistributor: Ubuntu\nErstellungsdatum: 06.05.2009
kde-open --version - kde about: Qt: 4.5.0\nKDE: 4.2.4 (KDE 4.2.4)\nKIO Client: 2.0
/etc/debian_version - squeeze/sid
/etc/issue - Ubuntu 10.04.3 LTS \n \l

Summary Script

#!/bin/bash

uname -a > uname_$(date +%Y-%m).txt
lsb_release -a > lsb_release_$(date +%Y-%m).txt
sudo dmidecode > dmidecode_$(date +%Y-%m).txt
echo "listing hardware..."
sudo lshw -html > lshw_$(date +%Y-%m).html
dmesg > dmesg_$(date +%Y-%m).txt
sudo lspci -knnv > lspci_$(date +%Y-%m).txt
sudo lsusb -v > lsusb_$(date +%Y-%m).txt
sudo lscpu > lscpu_$(date +%Y-%m).txt
echo "checking hard drive..."
sudo hdparm -ItT /dev/sda > hdparm_$(date +%Y-%m).txt
sudo smartctl -a /dev/sda > smartctl_$(date +%Y-%m).txt
sudo fdisk -lu > fdisk_$(date +%Y-%m).txt
sudo parted -s /dev/sda print unit s print free > parted_$(date +%Y-%m).txt
ifconfig > ifconfig_$(date +%Y-%m).txt
dpkg --get-selections > dpkg_$(date +%Y-%m).txt

Check Integrity

memtest86+
memtester 512M 1
smartctl --test=long /dev/sda
F3 - Fight Flash Fraud - "simple tool that tests flash cards capacity and performance to see if they live up to claimed specifications. It fills the device with pseudorandom data and then checks if it returns the same on reading."
H2testw - "lassen sich Speichermedien wie Festplatte oder Flash-Drive auf Fehler überprüfen und gelöschte Daten sicher überschreiben."

Check Performance

# hdparm -t --direct /dev/sda - benchmark direct disk reads
# hdparm -T /dev/sda - benchmark cached reads
$ 7za b -- benchmark

Modules

lsmod - list kernel modules.
modprobe <module> - add a loadable kernel module. Options: r: remove.
modinfo [module] - show info about a kernel module.
/etc/modules - contains modules loaded at boot.

Backup

partimage --nodesc save /dev/sda1 /media/backup/sda1_2010-08-31.partimg.gz - backup a partition
sudo partimage restore /dev/sda1 backup.partimg.gz - restore a partition
tar --one-file-system -cpf /media/backup/system.tar * - backup root file system (if run from /) in single mode, or from live CD (then run from /mnt)
tar -xf /media/backup/system.tar - restore the files (run on newly created partition), then update fstab and delete /etc/udev/rules.d/70-persistent-cd.rules and 70-persistent-net.rules; then update grub using chroot
see also tar examples above
rsync -ahrv --delete --delete-excluded --link-dest=../last / --files-from=backup-include.lst --exclude-from=backup-exclude.lst /media/backup/$(date +%Y-%m-%d) && ln -nsf /media/backup/$(date +%Y-%m-%d) /media/backup/last - make a copy of the specified files using hardlinks where possible via the "last" target, then make the current backup the last one with a softlink
rsync -avhH --info=progress2 /media/veracrypt2/backintime /media/veracrypt3/ - copy snapshots to new drive
Back in Time (rsync frontend, optional cronjob)

Fault Recovery

What to do if some application doesn't promptly respond? First, you should keep calm. Try to normally shut it down. After a minute or so (depending on the system load) you might let the desktop environment kill the application via window decoration's close button. You are likely to be asked if you really want to kill it, or to wait some more.
Anyway, you can launch your favorite task manager like top on terminal or gnome-system-monitor that allows you to watch the resources and kill or terminate applications.
If the graphical environment doesn't respond, then my next attempt would be to switch to a virtual console via CTRL-ALT-F1 or -F2, log in with superuser privileges, and to run top there.
If you aren't familiar with the console or top or simply aren't in the mood to log in, you can simply press CTRL-ALT-DEL in a virtual console to initialize a soft reboot.
A magic SysRq key combination (Alt + SysRq + some key) can send various commands to the kernel even if the system seems to be frozen. A common idiom to perform a safe reboot of a Linux computer which has otherwise locked up, the QWERTY mnemonic "Raising Elephants Is So Utterly Boring", "Reboot Even If System Utterly Broken" or simply remembering the word "BUSIER" backwards, is often useful: unRaw, tErminate, kIll, Sync, Unmount, reBoot. Wait a few seconds each.
TODO: Does this work with AltGr+SysRq+Key in case Alt+Print is used for screen capture in GNOME?
Other useful things: F = call oom_kill (out of memory killer); N = reset nice level; T = print task list
System Rescue CD

Set root password

on boot, in grub, edit command: add "1" to kernel line
the kernel will boot up to single-user mode
run the passwd command to set a new password

Access from other system (e.g. Live CD)

become root: sudo su
find partition: fdisk -l
mount partition: mkdir /media/sdb2; mount /dev/sdb2 /media/sdb2
check content: ls -a /media/sdb2
mount /dev: mount -o bind /dev /media/sdb2/dev
mount /proc: mount -t proc /proc /media/sdb2/proc
mount /sys: mount -o bind /sys /media/sdb2/sys
change root: chroot /media/sdb2

Run fsck on a VeraCrypt (TrueCrypt) volume

veracrypt -d crypted.hc - dismount if mounted
veracrypt --filesystem=none crypted.hc - mount the volume without mounting its filesystem
veracrypt -l - list mounted volumes
output will be: /dev/mapper/veracrypt1 (or similar)
sudo fsck -fC /dev/mapper/veracrypt1 - do the check
veracrypt -d crypted.hc - dismount
veracrypt --fs-options=rw,noatime crypted.hc mountpoint/ - remount

Copy disk to virtual disk

# dd if=/dev/sdc bs=1M | pv -s $(blockdev --getsize64 /dev/sdc) -B 1M | VBoxManage convertfromraw stdin mydisk.vdi $(blockdev --getsize64 /dev/sdc)
see also How to migrate existing Windows installations to VirtualBox

Make a compressed image of a dmcrypt partition

TODO

Overwrite a disk with zeroes for secure deletion, and show a progress bar

# dd if=/dev/zero bs=1M | pv -s $(blockdev --getsize64 /dev/sdc) -B 1M | dd of=/dev/sdc bs=1M
You might want to use /dev/urandom instead of /dev/zero, but this would be much slower, and it doesn't make much sense.
Alternatively, you could fully encrypt the disk and forget the key.
for details, see Step-by-Step Secure Erasing of a Data Storage Device

Data Recovery

Recovery from Physically Damaged Drive

apt-get install gddrescue - gddrescue with logfiles allows to be called multiple times and rescues only what is left untried; don't mistake for dd_rescue. See "info ddrescue" for good explanations and examples, e.g., how to find out which files are in bad areas of a disc.
ddrescue -s50M /dev/hdc hdimage.raw logfile.log - rescue most important parts first: copy first 50 MB
ddrescue -s1M -dr3 /dev/hdc hdimage.raw logfile.log - rescue important, try hard: copy first 1 MB, direct access, max-retries 3 times
ddrescue -i39G -s1G /dev/hdc hdimage.raw logfile.log - rescue end of disk (example disk would have a size of 40 GB)
ddrescue -i19G -s2G /dev/hdc hdimage.raw logfile.log - rescue middle of disk (example disk would have a size of 40 GB)
ddrescue -n /dev/hdc hdimage.raw logfile.log - rescue whole disk quickly: no-scrape (stop after trimming, saves time, reverses automatically)
ddrescue -dr3 /dev/hdc hdimage.raw logfile.log - rescue whole disk thoroughly: direct access, max-retries 3
ddrescue -dM /dev/hdc hdimage.raw logfile.log - re-try everything exhaustively: direct access, re-trim
ntfsinfo -m [-f] [device] - get NTFS information, e.g. cluster size, use -f if volume dirty, might have to mount via loopback
ddrescuelog -l- -b4096 logfile.log > badblocks.txt - prints a list of affected sectors/clusters when file system block (cluster) size is 4096
ntfscluster [-f] -c 206573-206585 [device] 2>> /dev/null - show file name for range of clusters, use -f if volume dirty, might have to mount via loopback
blkstat hdimage.raw 123456789 - determines the allocation status of the file system sector number (from badblocks); tool from sleuthkit
ifind hdimage.raw 123456789 - determines the inode associated with the sector (can take some time and CPU)
istat hdimage.raw 7654321 - shows affected file properties (maybe name, depends on file system) and its list of inodes
fls -rFp hdimage.raw > filelist.txt - prints a complete list of files
then you can make a backup copy of the image and mount it
see also: magicrescue to scan for lost files

Move /home to another mountpoint

check size of /home: du -sh /home
create an empty formatted partition that is large enough
log off, use terminal
find new partition: fdisk -l
mount new partition: mkdir /mnt/tmp; mount /dev/sda6 /mnt/tmp
sync content: rsync -avx --progress /home/ /mnt/tmp (cp is faster but don't guarantees consistency)
mount new /home: mount /dev/sda6 /home
check result: du -sh /home; mount|grep /home
unmount tmp: umount /home
remove old data: rm -rf /home/* (don't remove the folder itself)
get UUID of new partition: blkid|grep sda6
enter line to /etc/fstab: UUID=f72aac23-092f-4484-b35c-f222c106d716 /home ext3 defaults 0 2
leave chroot: exit
reboot

Hide partion from Nautilus

Idea: Nautilus shows those partitions that are mounted in /home or /media. To hide them, mount (or fake-mount) them elsewhere in /etc/fstab.
UUID=12345 /mnt/foo ntfs defaults,x-gvfs-hide 0 2
UUID=12345 /mnt/dontmount1 ntfs noauto 0 2

Mount GMX Mediacenter

# mount.davfs https://webdav.mc.gmx.net /mnt/gmx - you'll be asked for username and password (might use customer id)
https://webdav.mc.gmx.net /mnt/gmx davfs user,noauto 0 0 - fstab entry
https://webdav.mc.gmx.net gmx-username gmx-passwort - ˜/.davfs/secrets
$ mount /mnt/gmx - should now be able to mount as user
gmx-mediacanter mounten (linuxforen.de)

SSH Tunneling

kermit$ ssh -Cg -L 33306:jupiter:3306 localhost - tunnel from localhost:33306 to jupiter:3306.

VNC over SSH

helper# apt-get install openssh-server
helper# adduser afriend
helper$ vncviewer -listen
afriend# apt-get install x11vnc
afriend$ ssh-keygen -t rsa
from ~/.ssh/id_rsa.pub, copy key to helper's /home/afriend/.ssh/authorized_keys
$ ssh -f -L 5500:localhost:5500 afriend@helper.dyndns.org sleep 5; x11vnc -connect_or_exit localhost:5500

Internet Connection Sharing

use PC as router (de)
start dhcp3 server; activate IP forwarding; configure firewall and NAT

TV Cards

alsamixer -c[MY_DEVICE_NUMBER] - to activate sound on Asus MyCinema P7131 Hybrid.

Powersave

/etc/fstab - prefer relatime over atime.
cpufreq-info - list CPU frequency settings and capabilities.
cpufreq-set - change CPU frequency settings. Examples: -g ondemand|performance|powersave. Recommended: ondemand.
modprobe p4-clockmod - does NOT save power, only prevents overheating.
desktop effects (compositing) do not use more power. (Good power management practices)
Powersave heißt nicht Energie sparen

SSD Optimization

/etc/fstab: noatime tmpfs /tmp tmpfs defaults,noatime,mode=1777 0 0
Firefox:
enlarge ram cache: browser.cache.disk.enable = false
disable disk cache: browser.cache.memory.capacity ...
change scheduler: CFQ is good for HDD, deadline (or noop) are better for SSD:
/boot/grub/menu.lst - "kopt= ... elevator=deadline"
# echo 1 > /sys/block/sda/queue/iosched/fifo_batch
more: tombuntu.com

Use old OSS application with PulseAudio

padsp <program>

Tweaks

use relatime (or noatime) in /etc/fstab to speed up the hard drive
disable subpixel-hinting, use "best form" instead
disable unnecessary services
Ubuntu: don't use default theme "Murrina" (Human, StormCloud) - better use Xfce or Mist theme - Linux für ältere Rechner optimieren
Gnome:
/apps/gnome-power-manager/notify/low_power = false - don't warn on old battery;
/apps/gnome-power-manager/notify/perhaps_recall = false - dito;
/apps/metacity/general/reduced_resources = true - use wireframe instead of content while moving windows, and other;
/apps/update-notifier/auto_launch = false - disable update-notifier popup, show notification in panel instead;
/desktop/gnome/interface/enable_animations = false - don't use animations, e.g. on minimize window;
/desktop/gnome/interface/menus_have_icons = true - restore icons in menus (that are disabled by default in Ubuntu 9.10);
/desktop/gnome/interface/buttons_have_icons = true - dito;
/desktop/gnome/thumbnail_cache ... - limit size and age of thumbnails;
scale down Tracker:
uncheck "enable indexing"
set indexing speed to "slower"
check "minimize memory usage (slower indexing)"
add items to the list of ignored paths, if you never search them
uninstall tracker, if you don't need it ever: sudo apt-get remove tracker tracker-search-tool tracker-utils
add export MOZ_DISABLE_PANGO=1 to .bashrc to disable Pango font smoothing in Firefox (enabled by default in Ubuntu)
Tuning (de)

Network issues

eth0: link is not ready - might come from a Windows network driver that is incorrectly disabling the network adapter on shutdown; solution: reboot and power off to re-init the network adapter.
Speed limit for Apt to one source and to a maximum rate in kB/s: /etc/apt/apt.conf Acquire::Queue-mode "access"; Acquire::http::Dl-Limit "100";
Host name changed?
Check /etc/hostname and /etc/hosts.
Network card and/or MAC address changed?
Check /etc/udev/rules.d/70-persistent-net.rules and /etc/network/interfaces.

Configure EFI

efibootmgr - show current EFI boot configuration
sudo efibootmgr --bootorder 2,0,4 - change EFI boot order
sudo efibootmgr --bootnext 4 - select one-time EFI boot item

Misc Issues

Flash Problems

locate libflashplayer.so
should only have one out of /usr/lib/flashplugin-installer/ or /usr/lib/adobe-flashplugin/ or /usr/share/ubufox/plugins/ or ~/.mozilla/plugins or the like
improve performance with ATI: AccelMethod = XAA (?)
Flash 11.x requires CPU with SSE2 (since Pentium IV or Athlon 64): use 10.3 as long as it is supported
→ download flashplayer_10_plugin_debug.tar.gz and extract libflashplayer.so to ~/.mozilla/plugins/

File System Hierarchy

Info

/bin

This folder contains the most basic applications that have to be present on every Linux system, like the shell, tools for file and process management, and for string manipulation.

/boot

/boot/grub/menu.lst - grub 1.x boot menu

/dev

/dev/fd - floppy drive
/dev/hda - first hard disk drive
/dev/null - data sink
/dev/sdb3 - third partition on second scsi (or sata) disk drive
/dev/shm - virtual ramdisk (tmpfs), default size is half of RAM
/dev/urandom - unblocking random, faster than /dev/random, but much slower than /dev/zero
/dev/zero - data source (binary zero)

/etc

/etc/apt/preferences - priorities of package, allows pinning of versions
/etc/apt/sources.list - package sources; examples:
deb http://ftp.de.debian.org/debian woody main contrib non-free
deb file:///tmp/download ... ?
deb cdrom:[Ubuntu 9.04 _Jaunty Jackalope_ - Release i386 (20090420.1)]/ jaunty main restricted
/etc/conf.d/net - network configuration
/etc/ddclient.conf - client for dynamic dns; example:
protocol=dyndns2, use=if, if=ppp0, server=members.dyndns.org, login=foo, password='bar', myaddress1.dyndns.org,myaddress2.dyndns.org
/etc/default/... - default configurations (?)
/etc/environment - $PATH
/etc/exports - nfs shared directories (?), e.g. "/home *.domain.de(rw)" - user id counts for access rights
/etc/fstab - file system table
/etc/gdm/PostSession/Default - run on gnome session end (user logout); e.g. 'truecrypt -d'
/etc/hostname - name of the computer
/etc/hosts - hostname-to-address mappings
/etc/iftab - assigns persistent names to network interfaces. Example: eth0 mac 00:A0:24:51:8F:F4. (Ubuntu only till 7.04?)
/etc/inittab - defines what each runlevel does (?)
/etc/init.d/ - init scripts for running services. Examples:
sudo /etc/init.d/sshd [start|stop|restart]
sudo /etc/init.d/hal restart
/etc/issue - is displayed on console login prompt (before a user logs on), can hold some escape sequences like \n=nodename; issues.net is used by SSH
/etc/mke2fs.conf - default settings for new file systems
/etc/modules - kernel modules loaded at boot, e.g. fuse, it87
/etc/motd - is displayed on console login (after a user logs on), can hold some escape sequences like \n=nodename; is re-created on boot
/etc/motd.tail - is appended to motd (optional)
/etc/mtab - table of mounted file systems
/etc/network/interfaces - network interfaces
/etc/openoffice/sofficerc - set Logo=0 for speedup
/etc/passwd - basic user configuration: username:password:UID:GID:name:home:shell - if password is 'x' then stored in /etc/shadow
/etc/rc?.d/ - links used by init and managed by update-rc.d
/etc/rc.local - is executed after each runlevel change (?)
/etc/resolv.conf - address resolution, DNS server etc.
/etc/shadow - password hashes, restricted access
/etc/ssh/sshd_config - sshd config; e.g. set 'PermitRootLogin no'
/etc/skel/ - template for new user profiles
/etc/sudoers - list of who is allowed to run what as super user
%admin ALL=NOPASSWD: /bin/mount # allow members of group admin to not need a password (note that later entries override this)
%admin ALL=NOPASSWD: /bin/umount
%admin ALL=NOPASSWD: /usr/bin/truecrypt
/etc/sysfs.conf - tune hardware settings, e.g. CPU frequency scaling:
devices/system/cpu/cpu0/cpufreq/scaling_governor = ondemand
devices/system/cpu/cpu0/cpufreq/ondemand/up_threshold = 90 # default 95; 90 to better trigger flash videos in firefox (run with 'taskset -c 0')
/etc/udev/rules.d/70-persistent-net.rules - e.g. assign ETH0 to MAC address
/etc/X11/xorg.conf - X configuration: monitors, graphics cards, keyboards, mice
/etc/xdg/autostart - autostart .desktop files for all users.

/lib

This folder contains shared libraries for the essential programs that are required for booting up the machine.
/lib/modules - kernel libraries

/lost+found

This folder takes fragments of files that are recovered after a crash.

/media

This folder holds dynamically mounted filesystems like CD-ROM or USB sticks.

/mnt

This folder holds temporary mounted partitions.

/opt

This folder contains large applications that are not handled by the package manager, and/or don't observe the standards hierarchy.

/proc

/proc/... - shows info about system
/proc/acpi/info - general ACPI info (e.g. version)
/proc/acpi/sleep - list of S-states the BIOS knows (e.g. S0 S3 S4 S5)
/proc/asound/cards
/proc/bus/... input|pccard|pci|usb
/proc/cmdline - contains the command line that Grub starts the kernel with
/proc/cpuinfo
/proc/dma
/proc/ide/hda/geometry
/proc/ide/hda/settings
/proc/interrupts
/proc/meminfo
/proc/mounts
/proc/partitions
/proc/scsi/scsi - also SATA
/proc/swaps
/proc/sys/dev/cdrom/info
/proc/uptime
/proc/version

/root

This is the home directory of the superuser that must be located on the same filesystem as the root directory.

/sbin

This folder contains the most essential tools for system management that are usually run by superuser only.

/sys

/sys/block/sda/queue/scheduler - I/O scheduler
/sys/devices/system/cpu/cpu0/cpufreq/* - CPU frequency stuff
/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq - current frequency (kHz)
/sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq - current frequency (kHz)
/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor - current governor (recommended: ondemand)
/sys/devices/system/cpu/cpu0/cpufreq/stats/time_in_state - table of speed state (kHz) and time (s)
/sys/... - ... ?

/tmp

This folder holds temporary files for all users. The sticky bit means that users are only allowed to access their own files.

/usr

/usr/bin - common applications
/usr/include - source code header files of devel-packages
/usr/lib - libraries of the common applications that are managed in /usr
/usr/local - applications that are not handled by the package manager, e.g. self-compiled
/usr/sbin - system management applications
/usr/share - shared files, architecture-independent; icons, wallpapers, documentation, etc.
/usr/share/application/*.desktop - application starters
/usr/share/locale - localization files of the applications
/usr/share/man - man-pages
/usr/src - source code files of devel-packages

/var

/var/cache/apt/archives - apt package cache, use apt-get clean to delete all
/var/lib/dpkg/available - list of all available packages
/var/log/apt/history.log - APT history (TODO: is this Synapic's History?)
/var/log/boot.log - logged on system startup, e.g., fsck, kernel modules, services
/var/log/dpkg.log - DPKG log (TODO: is this written by CLI apt-get?)
/var/log/messages - kernel messages
/var/log/syslog - kernel messages (debian/ubuntu, mandriva)
/var/www - web server files

~

~/.cache == $XDG_CACHE_HOME
~/.cache/rhythmbox/jamendo/dbdump.xml - dump of Jamendo database
~/.config == $XDG_CONFIG_HOME
~/.config/autostart - autostart .desktop files
~/.config/gtk-3.0/bookmarks - GTK Bookmarks (a.k.a. Thunar Places, Favorites); formerly stored at ~/.gtk-bookmarks
~/.config/user-dirs.dirs - default directories (documents, pictures, music etc.)
e.g., XDG_DESKTOP_DIR="$HOME/Desktop"
~/.config/user-dirs.locale - default locale, e.g., de_DE
~/.local/share == $XDG_DATA_HOME
~/.local/share/applications/*.desktop - application starters. Don't forget to set executable flag. Example:
[Desktop Entry]
Version=1.0
Type=Application
Exec=x11vnc -connect 123.456.78.9 -nopw
Name=Support from a Friend with VNC
Comment=Remote Control
Terminal=true
Icon=/usr/share/icons/Humanity/apps/48/vinagre.svg
~/.local/share/rhythmbox/rhythmdb.xml - Rhythmbox database
~/.local/share/Trash/files - trash folder (Gnome only?)
~/.profile - is executed at login (?)
~/.nanorc - syntax highlight: include "/usr/share/nano/html.nanorc" (also e.g. c, perl, sh)
... -

Distribution Specific

Ubuntu

boot options:
maxcpus=X - use X cpus
nosmp - disable multicore support
noapic, noagp, noapm - disable APIC, AGP, or power management
nolapic - disable local APIC (?)
pci=noacpi - disable ACPI during PCI configuration
acpi=off - disable ACPI completely
acpi=force - enable ACPI by force
vga=normal - disable framebuffer
vga=... - configure resolution of grub and console
ht=on - enable hyper threading
pci=nomsi - disable Message Signaled Interrupts (perhaps helps with SATA problems)
pci=bios - ?
pci=routeirq - IRQ auto routing
usb=bios - ?
fb=false - disable framebuffer
DEBCONF_DEBUG=5 - detailed error search (?)
BOOT_DEBUG=2|3 - error search during startup (?)
all_generic_ide - use generic IDE driver
xforcevesa - X server uses Vesa by force
nomodeset - disable kernel mode setting (KMS), since Karmic
noplymouth - disable plymouth, replaces nosplash, since Lucid
i915.modeset=0|1 - workaround for graphics boot issues with Lucid (set to 1 to activate KMS helps on some laptops, set to 0 for some nVidia?)
radeon.modeset=0 - workaround for graphics boot issues with Lucid and kernel mode setting)
i915.i915_enable_rc6=1 - enable Sandy Bridge energy saving RC6 (if BIOS is ok)
noefi - run installer in legacy BIOS mode when started from UEFI-BIOS
Turn off or limit the Recent Documents feature in Gnome
Notebook-Harddrive-Bug
Troubleshooting Adobe Flash in Ubuntu (2008)
How to add Thunderbird to the Ubuntu Messaging Menu
How to fix ubuntu 10.04 LTS (lucid) blank Screen at startup
10 things to do after installing Ubuntu
nice themes for ubuntu 10.04 lucid
known ubuntu 10.4 lucid issues with workarounds
how to install skype in Ubuntu from skype repository
Important Tweaks/Things to do After install of Ubuntu 12.04 Precise Pangolin - e.g., activate hibernate
Some More Tweaks for Ubuntu 12.04 Precise Pangolin
Nautilus statt Thunar als Desktop unter XFCE
Fix unable to shutdown / reboot / logout when OpenOffice Quickstarter is active:
sed -i '5s|true|false|g' /usr/lib/openoffice/basis3.*/share/registry/data/org/openoffice/Office/Recovery.xcu - change DocumentStoreUIEnabled in Recovery.xcu to false
clear /home/user/.openoffice.org/3/user/registry/cache
for LibreOffice: /usr/lib/libreoffice/basis3.3/share/registry/main.xcd
Bug #562027 in Launchpad
/etc/default/acpi-support
ENABLE_LAPTOP_MODE=true - # Switch to laptop-mode on battery power
see also: /etc/laptop-mode/laptop-mode.conf
.hidden contains a list of files or folders to hide in Nautilus, e.g. lost+found
manual upgrade: sudo do-release-upgrade (terminal), or gksudo "update-manager -c" (graphical)
Hint: it might be required to switch the default behavior for the release upgrader in /etc/update-manager/release-upgrades (Prompt=never|normal|lts) matching the current (old) installation, especially if an upgrade from a non-LTS version to an LTS version is to be done.0
Recommended packages installed by default: In accordance with the Debian Policy Manual (which says "The 'Recommends' field should list packages that would be found together with this one in all but unusual installations"), the package management system now installs packages listed in the Recommends: field of other installed packages as well as Depends: by default.
If you want to avoid this for specific packages, use apt-get --no-install-recommends; if you want to make this permanent, set APT::Install-Recommends "false"; in /etc/apt/apt.conf. Be aware that this may result in missing features in some programs. (This change was made in Ubuntu 8.10.)
screen flicker on shutdown: set native resolution in usplash.conf, or activate splash if disabled.
program not translated after upgrade: re-install language package.
reset tracker: tracker-processes -r
my potential post-installation package selection for Ubuntu Lucid:
Localization: firefox-locale-de (since ff9) language-support-de thunderbird-locale-de (already in default Lucid: language-pack-de language-pack-gnome-de language-support-writing-de openoffice.org-help-de)
System: backintime-gnome dkms galternatives gparted mesa-utils numlockx preload rcconf smart-notifier wine
Applications: audacity dia-gnome ekiga gnucash gpaint gramps inkscape libreoffice-pdfimport p7zip-full pdfshuffler ripperx scribus scribus-doc (already in default Lucid: openoffice.org-gtk)
Multimedia: adobe-flashplugin audacious-plugins-extra avidemux comix denemo exaile gnome-alsamixer gnome-mplayer gstreamer0.10-plugins-ugly lame mencoder mozilla-mplayer mozilla-plugin-vlc optipng totem-mozilla ubuntu-restricted-extras vlc
Network: amule ddclient dnsmasq filezilla nmap ntp pidgin pyNeighborhood samba squid thunderbird-gnome-support traceroute x11vnc xtightvncviewer
Advanced: cryptsetup dosbox ghex gufw leafpad ntfs-3g pdftk seahorse-plugins sun-java6-plugin sun-java6-jre tracker unace-nonfree virtualbox-ose xmp-audacious
Games small: ace-of-penguins atomix billard-gl glchess moon-lander pinball pioneers sopwith xfrisk
Games large: 0ad alien-arena beneath-a-steel-sky boswars extremetuxracer flightgear flight-of-the-amazon-queen freeciv-client-gtk freeciv-sound-standard lincity-ng megaglest nexuiz openarena pingus sauerbraten supertux supertuxkart torcs tremulous vegastrike warsow warzone2100 wesnoth widelands
Hardware: computertemp cpufrequtils cpuid hardinfo hardware-monitor hddtemp hwinfo inkblot lm-sensors lshw-gtk sensors-applet smartmontools sysfsutils x86info xmbmon xsensors
Developer: ant build-essential doxygen geany graphviz kdiff3 meld nautilus-compare nautilus-gtkhash netbeans rabbitvcs-nautilus rapidsvn rkward shed sloccount subversion sun-java6-jdk sun-java6-source texlive texlive-lang-german texlive-latex-extra texmaker
Geek: boinc conky human-icon-theme human-theme
Recovery: gddrescue partimage secure-delete testdisk
Xubuntu: baobab epiphany-browser gnome-disk-utility gnome-system-log gthumb ristretto thunar-gtkhash xfce4-datetime-plugin xfce4-goodies xubuntu-restricted-extras
Precise: gdebi gimp indicator-multiload lo-menubar synaptic
purge if not required:
Menu: indicator-me indicator-messages
Bluetooth: bluez bluez-alsa bluez-cups bluez-gnome bluez-gstreamer bluez-utils pulseaudio-module-bluetooth
Empathy: empathy empathy-common nautilus-sendto-empathy
Evolution: evolution evolution-common evolution-couchdb evolution-data-server evolution-exchange evolution-indicator evolution-plugins evolution-webcal
Gwibber: gwibber gwibber-service libgwibber0
Mono: f-spot gbrainy mono-2.0-gac mono-csharp-shell mono-gac mono-gmcs mono-runtime sysinfo tomboy
Hardware: brltty pcmciautils
Accessibility: brltty onboard
Xubuntu: orage
additional package sources:
GIMP: http://ppa.launchpad.net/otto-kesselgulasch/gimp/ubuntu precise main
Mediainfo: http://ppa.launchpad.net/shiki/mediainfo/ubuntu precise main
Pidgin: http://ppa.launchpad.net/pidgin-developers/ppa/ubuntu precise main
Back in Time: http://ppa.launchpad.net/bit-team/stable/ubuntu precise main
Wine: http://ppa.launchpad.net/ubuntu-wine/ppa/ubuntu precise main
RabbitVCS: http://ppa.launchpad.net/rabbitvcs/ppa/ubuntu precise main
Geany: http://ppa.launchpad.net/geany-dev/ppa/ubuntu precise main
Toolchain (GCC): http://ppa.launchpad.net/ubuntu-toolchain-r/test/ubuntu trusty main
Sensors Applet: http://ppa.launchpad.net/darxus/sensors-applet/ubuntu precise main
GetDeb: http://archive.getdeb.net/ubuntu precise-getdeb apps games
VirtualBox: http://download.virtualbox.org/virtualbox/debian precise contrib non-free
VideoLAN ftp://ftp.videolan.org/pub/debian stable/

Create Mini Installer Device using UEFI:
format drive with GPT, create FAT32 partition (or NTFS should work, too)
get 64 bit mini.iso and extract "linux" and "initrd.gz" to /mini on new partition
extract /boot/grub/efi.img to temp location, mount it
copy /efi/boot/bootx64.efi to new partition
create /boot/grub/grub.cfg like this:
```
		menuentry 'Ubuntu Alternate Installer' {
			set gfxpayload=keep
			linux	/mini/linux ---
			initrd	/mini/initrd.gz
		}
```
... no need to install grub.

Xubuntu

Setup "Start-Menu" key (Super_L) to open Xfce-Menu:
1. create keyboard shortcut in xfce settings (will be "Super+Super_L")
2. edit ~/.config/xfce4/shortcuts/name_of_your_shortcuts.xml
3. remove "Super+" from the respective entry
4. open and close shortcut configuration, or restart X to activate
Problem: the key doesn't work as modifiert (as in Super+e) any more.
Workaround: don't use Super_L for menu, but something like Super+w.
Enable Gigolo to open Thunar with doubleclick on mounted SMB volume:
1. # apt-get install gvfs-fuse fuse-utils - install GVFS backend so that GVfs mounts the remote resources in ~/.gvfs
2. # gpasswd -a username fuse - add user to the fuse group
3. $ nano ~/.local/share/applications/defaults.list x-directory/gnome-default-handler=Thunar.desktop inode/directory=Thunar.desktop x-directory/normal=Thunar.desktop - enable Thunar to open folders by gvfs-open
4. You might have to relaunch your session.
5. See Open resources in Thunar on Xfce 4.4 and 4.6 (uvena.de)

Do not shorten (ellipsize) text on Xfce desktop, edit ~/.gtkrc-2.0:

style "xfdesktop-icon-view" {
	XfdesktopIconView::ellipsize-icon-labels = 0
}
widget_class "*XfdesktopIconView*" style "xfdesktop-icon-view"
widget "*XfdesktopIconView*" style "xfdesktop-icon-view"
class "*XfdesktopIconView*" style "xfdesktop-icon-view"

Getting Back to a Pure Xubuntu

Knoppix

http://knopper.net/knoppix/
most important boot options:
failsafe - minimum hardware detection; if this does not run, the is almost no hope
knoppix 2 - runlevel 2, textmode only
knoppix lang=de - specify language/keyboard
knoppix screen=1280x1024 - use specified screen resolution for X
knoppix xvrefresh=60 - use 60 Hz vertical refresh rate for X
knoppix fb1024x768 - use fixed framebuffer graphics
knoppix noapic - disable apic
knoppix nousb nofirewire - disable usb and firewire
knoppix vga=normal - disable framebuffer mode
knoppix nodma - disable dma (very slow)
knoppix noideraid - disable raid detection (if raid available)
knoppix nopcmcia - disable pcmcia detection (on laptops)
knoppix acpi=off - disable acpi
knoppix pnpbios=off - disable pnp bios initialization
full options: ftp://ftp.uni-kl.de/pub/linux/knoppix/knoppix-cheatcodes.txt

Game Equivalents/Clones

Civilization: Freeciv
Dune, Command & Conquer (Real-time Strategy): Bos Wars, Warzone 2100
Lemmings: Pingus
Raptor: Chromium
Settlers: Pioneers
(Shooter): Alien Arena, Nexuiz, Open Arena, Sauerbraten, Warsow
Sim City: Lincity-NG
(Turn-based Strategy): Battle for Wesnoth

Linux

Why?

Advantages

Handicaps

More

Findings

Basics

Keys and Shortcuts

Shell

Files and Streams

System

Debian Package Management

User

Network

Devices

Graphics

Shell Programming

Programming

Configuration

Software Packages

Advanved

System Info

Live CPU/RAM/Swap Monitoring

Mainboard

CPU

Memory

Graphics

Network

Storage

Devices

Software

Summary Script

Check Integrity

Check Performance

Modules

Backup

Fault Recovery

Set root password

Access from other system (e.g. Live CD)

Run fsck on a VeraCrypt (TrueCrypt) volume

Copy disk to virtual disk

Make a compressed image of a dmcrypt partition

Overwrite a disk with zeroes for secure deletion, and show a progress bar

Data Recovery

Recovery from Physically Damaged Drive

Move /home to another mountpoint

Hide partion from Nautilus

Mount GMX Mediacenter

SSH Tunneling

VNC over SSH

Internet Connection Sharing

TV Cards

Powersave

SSD Optimization

Use old OSS application with PulseAudio

Tweaks

Network issues

Configure EFI

Misc Issues

Flash Problems

File System Hierarchy

Info

/bin

/boot

/dev

/etc

/lib

/lost+found

/media

/mnt

/opt

/proc

/root

/sbin

/sys

/tmp

/usr

/var

~

Distribution Specific