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

Contents 1 Screen 2 TeX 3 Network 4 ACPI 5 Suspend 6 init.d 7 Apache 8 Modules 8.1 Update alsa from source 9 services 10 kernel params 11 console tricks 12 shell scripts 13 mail 14 system info 15 Keyboard 15.1 xmodmap 16 File System 17 i18n files 18 Alt-SysRq 19 Baby Mode 20 KDE 21 xorg 22 vim 23 DNS 24 clock 25 iptables 26 See Also 27 Links

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 -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

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

Suspend

Suspending to disk/ram is kind of black magic. It depends a lot on the hardware and OS. Here is what worked for me on Ubuntu Feisty on an ASUS F3JC (this got me on the right track):

• install µswsusp (use apt, the link is just for info)
• s2disk just works (as root, of course)
• s2ram sais "unknown machine", but s2ram -f works fine. more info here.
• So, edit /usr/lib/hal/scripts/linux/hal-system-power-hibernate-linux resp. hal-system-power-suspend-linux to use that instead of pmi (which is otherwise the first thing it finds and tries).

The only thing that does not quite work is the sound driver: i need to reload the snd_hda_intel module after waking the max up. Annoying, but I can live with it. I could hack it into s2ram, but the problem is that you have to kill all programs using sound in order to reload the module. I for one don't want that to happen automatically.

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

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 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

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.

See Also

• Category:Shell scripts

Links

• Linux Commands Line list (Linux Guide)
• D's list
• Unix Toolbox
• IBM's 10 essential tricks for admins
• IBM's 10 good UNIX usage habits
• TuxRadar: linux tips and more linux tips
• BASH FAQ
• Linux Commands @ FLOSS Manuals (use menu on the left)
• FLOSS Manuals: Command Line Intro (note navigation on the left)
• commandlinefu
• pixelbeat's cheat sheet
• fosswire's cheat sheet
• Linux-Unix cheat sheets - The ultimate collection