Linux Cheat Sheet

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Some things handy to know when dealing with a Linux shell. Unsorted, incomplete, subjective list.

Screen

screen: starts a new screen session (vistual console)
ctrl-a d: disconnects from a session
screen -rd: reconnects to a session;
ctrl-a esc: copy mode, for selecting and scrolling. Hit esc again to get out.
ctrl-a 0: selects window 0. (works for all numbers to 9)
ctrl-a ": list windows
ctrl-a Ctrl-c: new window

TeX

texhash

refresh file database (after manual install) -- this is for tetex (and texlive?); MiKTeX uses initexmf -u

manual install of ctan packages

latex *.ins (extracts styles, etc)
latex *.dtx (makes documentation)
move styles, etc to /usr/share/texmf-*/tex/xxx
update file database

renaming auto-generated sections

\listofalgorithms: \renewcommand{\listalgorithmname}{Algorithmenverzeichnis}
\printglossary: \renewcommand{\nomname}{Glossar}

Network

arp -a: show everything on the local link
arp -na host: show ARP entry
arping host: ARP-ping host
mtr: Like ping and tracepath combined
netdiscover: look who's on the network
socat: netcat's big brother
the obvious: ping, tracepath, nmap, netstat, nettop
monitoring: tcpdump, tcpick, tcpspy, iperf
download mms stream: mplayer mms://.....foo.wmv -dumpstream -dumpfile foo.wmv
tcpdump -w test.pcap -s 1550 dst 91.198.174.2 and tcp port 80: capture traffix on port 80 to a given IP
tcpflow -i any -C -e port 12345: capture tcp traffic from/to port 12345
iptables -A OUTPUT -p tcp --dport 12345 -j REJECT --reject-with tcp-reset: kills connections to a specific port

= SSL

penssl s_client -state -debug -connect host:port: detailed debug trace of SSL handshake. Good way to find out what cypher is used.

ACPI

echo 105:95:85:75:70 > /proc/acpi/thermal_zone/THRM/trip_points: set thermal trip points
echo 5 > /proc/acpi/thermal_zone/THRM/polling_frequency: set polling frequency

To show thermal status:

cat /proc/acpi/thermal_zone/THRM/temperature
cat /proc/acpi/thermal_zone/THRM/state
cat /proc/acpi/processor/*/limit
cat /proc/acpi/processor/*/throttling

Couldn't figure out where to configure that, so i write myself a small init.d script to set trip points and polling (which was disabled per default, causing overheating & reboots - thanks Feisty...)

cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies: show available cpu frequencies. Use scaling_cur_freq to get current frequency, cpuinfo_cur_freq appears to get confused about cpu numbers.
cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors: show available cpu governors (scaling policies). Use scaling_governor to get current frequency.
/usr/bin/cpufreq-selector: CPU frequency settings, provided by package gnome-applets (for whatever reason); -f: set frequency; -g: set governor

Power Management

Per default, GNOME uses the estimated time to discharge to trigger emergency hibernation. This sucks if you have a wonky battery. To force GNOME to use the percentage charged to trigger hibernation, use this:

gconftool-2 --type bool --set /apps/gnome-power-manager/general/use_time_for_policy false

To see all power management settings, use:

gconftool-2 --s /apps/gnome-power-manager/general

gconftool-2 --s /apps/gnome-power-manager/thresholds

init.d

initctl (start, stop, status)

control init jobs

/etc/inittab

control runlevels, inaddition to /etc/rc*.d

init, telinit

switch runlevel (0: halt; 1: single-user; 2-4: multi-user cli; 5: multi-user X; 6: reboot; S,s: swicth to single-user; a-c: on-demand)

update-rc.d

configure job start/stop at runlevel (or even remove job from rc*.d)

System administrators are not encouraged to use update-rc.d to manage runlevels. They should edit the links directly or use runlevel editors such as sysv-rc-conf and bum instead.

telinit level

sets the runlevel

S: single user, no network, no deamons
0: halt
1: single user, no network, no deamons
2: multi-user, no network, no deamons
3: multi-user, text
4: unused
5: multi-user, with X
6: reboot

Apache

To temporarily disable some page: Redirect 503 /path/to/page.html

Modules

Update alsa from source

sudo apt-get install module-assistant
sudo m-a update
sudo m-a prepare
sudo m-a a-i alsa
sudo alsa force-unload
sudo depmod -ae
sudo modprobe snd-hda-intel

I needed to do this on Hardy Heron to get alsa to work properly

services

gpm: console mouse service (because i always forget what it's called)

kernel params

vga=791: 80x50 characters vga text mode for virtual console (for some reason, this screws with the boot splash though)

console tricks

(some from [1])

fuser -k /media/cdrom: kill processes using /media/cdrom
reset: restore a hosed terminal to normal
ctrl-q: wake up terminal after suspend with ctrl-s
screen -S foo: start a screen session named "foo"
screen -x foo: join screen session named foo without disconnecting the other terminal. Input and putput works for both!.
tail -n +2: passes all but the first line of output. Useful for stripping headers
start-stop-daemon --start: starts a given program only if its not already running. Supports various options, see man page.
supervise: starts a program and restarts it when it dies. Supplied by daemontools/svtools.
sed -n '3~3p': print every 3rd line
awk '{if (++count%3==0) print $0;}: print every 3rd line
perl -ne 'print if($.%3==0)': print every 3rd line
readlink -f: resolve to absolute, real path. Poor man's realpath.
ls -1 | tr '\n' ':': list of files names separated by ":" (nice for building a path)
read x y z <<< "$foo": break a variable into words [2]
read x y z < <(echo a b c): piping something into read [3]
cat /proc/loadavg: system load, without calling uptime
cut -c1-80: truncate lines at 80 chars
fold: wrap lines
set -o ignoreeof: do not terminate shell on EOF
shell function for pasting to a bin: pastebin() { curl -F 'sprunge=<-' http://sprunge.us/; }
[[ $0 = /* ]] && echo "$0" || echo "$PWD/${0#./}": determin a script's own location (hopefully). see http://mywiki.wooledge.org/BashFAQ/028 for a full discussion.
pv: measure throughput through a pipe. handy to show progress on long running pipe jobs.
rsync -r A/ B/: copy the content of directory A into directory B (including all dot files, etc). Note that A/ will copy the contents of A, while just A will copy the directory (with its contents).
(thanks to hyphenated of #bash for this one)

SSH / Login

passwd -d <user>: disables password-based login for that user, both via ssh and locally. Unlike passwd -l, the acccount is not expired, and can be accessed via public key authentication, etc.
getent passwd <user>: look up the user not only in /etc/passwd but also NIS, LDAP, Samba, etc.
shopt | grep login_shell: is this a login shell?
echo $TERM | grep linux: is this a (linux) text terminal (vterm)?
export TMOUT=300: cause shell to automatically close after 5 minutes of inactivity.

shell scripts

set -e: script exists on any error.
set -u: treat unset variables as errors

mail

mutt -x -a somefile -s "some message" your@address < /dev/null: send mail with file attachment from the command line (no body)

system info

from [4]

cat /proc/cpuinfo: cpu make, speed, etc
dmidecode: BIOS info
ethtool -i eth0: network card info

Keyboard

loadkeys keymaps-file

xmodmap

keycode 66 = ISO_Level3_Shift: Makes CapsLock behave like AltGr - nice for programmign on a german keyboard

Configuration can be done in ~/.Xmodmap.

To execute automatically, put this into your ~/.xsessionrc:

 if [ -f ~/.Xmodmap ]; then
       xmodmap ~/.Xmodmap
 fi

To find out key codes, use xev

My .Xmodmap file:

keycode  66 = ISO_Level3_Shift
keycode  49 = asciicircum degree notsign notsign dead_circumflex dead_abovering
keycode  21 = apostrophe grave cedilla cedilla dead_acute dead_grave
keycode  34 = udiaeresis Udiaeresis diaeresis diaeresis dead_diaeresis dead_diaeresis
keycode  35 = plus asterisk asciitilde macron asciitilde dead_tilde

File System

lsof name: shows processes using a file or device

i18n files

Merge Multiple .po files into one: msgcat /tmp/*.po | msgfmt -o l10n/fr_CA/LC_MESSAGES/civicrm.mo -
Compile: msgcat *.po | msgfmt -o civicrm.mo -

Alt-SysRq

Alt-SysRq-something lets you talk directly to your system. See [5] for a list of commands. Here are the meanings of a few Alt-SysRq keys:

h: help
i: kill all processes, except ini
t: dump current tasks
b: dirty reboot (no disk sync!)
o: dirty shutdown

See /proc/sys/kernel/sysrq to find out if Alt-SysRq is enabled.

To trigger a SysRq programatically, use echo x > /proc/sysrq-trigger

Baby Mode

xtrlock: lock input but not the screen until pw is entered

KDE

save current session:
dbus-send --dest=org.kde.ksmserver /KSMServer org.kde.KSMServerInterface.saveCurrentSession

xorg

xrandr: manipulate video mode & resolution at runtime
xbindkeys: bind hotkeys

vim

:set paste: enable past mode, disable auto-indent
:syntax on: enable syntax highlighting
:w !sudo tee %: save file with root permissions

DNS

dnsmasq

host foo 192.168.0.1: lookup at a specific host
host -t srv foo: lookup of a specific record type
dig foo @192.168.0.1: detailed lookup with dig, at a specific host

When changes to DNS fail to take effect:
- check /etc/hosts for hard coded entries
- check /etc/resolv.conf for which DNS server will be used
- restart dnsmasq if running
- restart nscd if running

getent hosts <hostname>: resolves the host name, but also considers /etc/hosts (which host and dig don't do)

clock

in /etc/default/rcS set UTC=yes
use hwclock --set --utc --date="...."

iptables

log outgoing tcp connections to port $foo: iptables -A OUTPUT -p tcp -m state --state NEW --dport $foo -j LOG --log-ip-options --log-tcp-options --log-prefix "DIRTY FOO: " --log-uid --log-level warn
see output with dmsg or via syslogd.

harddisk

hdparm: tweak disk parameters
hdparm -t <device>: raw read benchmark
fio: advanced i/o benchmarks
blkid: show labels and uuids for block devices

gnome

pulseaudio -k: kill
start-pulseaudio-x11: (re)start
gnome-session-save --kill: terminate session (with gui prompt)
/etc/init.d/gdm restart: kill all sessions (no prompt)
unity --replace --display :0 & disown: (re)start unity without losing the current session. also works from a ctrl-alt-f4 virtual console.
compiz --replace --display :0 & disown: (re)start compiz (and unity) without losing the current session. also works from a ctrl-alt-f4 virtual console.
gsettings set org.gnome.desktop.interface text-scaling-factor 0.9: set font scaling catory to 0.9

Toolbox

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