Tips And Tricks

In this page I will share you some random tips and tricks I use in my daily life, and I will update this post frequently. Some of them will be commented, but not all.

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Generate random strings

tr -cd '[:alnum:]' < /dev/./urandom | fold -w12 | head -n4

You can use these string for example as random generated passwords.

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Run simple python http server

`nohup python -m SimpleHTTPServer 8888 >>../access.log &`

This will create a very simple http server on port 8888. Useful for shearing files quickly and easily over http protocol.

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Poor man's VPN with sshuttle

sshuttle -r [USER]@[HOSTNAME] 0.0.0.0/0 --dns -v

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Split MP3 into equal time length slices

Install required package:

apt-get install poc-streamer

Split into 3mins slices:

mp3splt  -t  3.00  [MP3 FILE] -o @n

Output will be: 01.mp3, 02.mp3, 04.mp3 . . . .

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Convert Video to 1280X (lower quality)

It us useful when you want to convert your video files to lower quality. Command:

avconv -y -i $MOVIE -vf "scale=1280:trunc(ow/a/2)*2" -vcodec libx264 -acodec libmp3lame $NEWNAME

Where:

• -y overwrite output files
• -i input files
• -vf scale=1280:trunc(ow/a/2)*2" --> Keep original ratio, and avoid "height not divisible by 2" error message.
• -vcodec libx264 --> video codec
• -acodec libmp3lame --> audio codec

You can replace "1280" to any other values which is divisible by 2. (640,480,etc...)

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LUA - delay function

Sometimes you have to use delay before the next function, and in this situation can be useful this little function.

function sleepAndContinueWithCommand(command)
    print("sleepAndContinueWithCommand Function")
    tmr.alarm(6,2000,tmr.ALARM_SINGLE, function()
        command()
   end) 

How to call it? sleepAndContinueWithCommand(FUNCTION_NAME)

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Modify Post Width of Ghost Blog

Change max-width in this section

/* Every post, on every page, gets this style on its <article> tag */
.post {
    position: relative;
    width: 80%;
    max-width: 1000px;
    margin: 4rem auto;
    padding-bottom: 4rem;
    border-bottom: #EBF2F6 1px solid;
    word-wrap: break-word;
}

Limit OprengePI CPU cores (enable/disable cores)

echo 1 >/sys/devices/system/cpu/cpu0/online
echo 0 >/sys/devices/system/cpu/cpu1/online
echo 0 >/sys/devices/system/cpu/cpu2/online
echo 0 >/sys/devices/system/cpu/cpu3/online

Check CPU temperature:

/sys/devices/virtual/thermal/thermal_zone0/temp

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tar from/to remote machine

tar from remote machine:

ssh root@172.16.0.240 "tar cfz - /etc /opt" >output.tar.gz

tar to remote machine:

tar cvf - *.sh | ssh vinyo@172.16.0.240 "cat  >~/test.tar.gz"

untar from remote machine

ssh vinyo@172.16.0.240 "cat ~/test.tar.gz" | tar xv  #OR
ssh vinyo@172.16.0.240 "cat ~/test.tar.gz" | tar xvf - 

untar to remote machine

cat test.tar.gz | ssh 172.16.0.250 "cd /home/vinyo/temp ; tar xv" #OR
cat test.tar.gz | ssh 172.16.0.250 "cd /home/vinyo/temp ; tar xvf -"

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Raspberry - prevent to sleep Wifi

Find your Wifi chip module: ls -la /sys/module/
Mine is: /sys/module/8189es/
Check power management status:
cat /sys/module/8189es/parameters/rtw_power_mgnt If it is equal to 0 then you are OK. If not, create a file something like this:

cat /etc/modprobe.d/8189es.conf 
options 8189es rtw_power_mgnt=0 rtw_enusbss=0

Restart.

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Rename OpenVZ container

vzctl set [CTID] --hostname [NEW HOSTNAME] --save

Unzip Each .zip File To Separate Directory

You have to be in the directory which contains the .zip files.

for Z in $( find . -type f -name '*.zip') ; do B=$( basename $Z ) ; F=${B%.*} ; mkdir $F ; unzip $Z -d $F ; done

Read Parameter File In Linux Shell (bash)

while IFS='=' read -r key value
do
    echo "... $key='$value'"
    eval "$key='$value'"
done < $PARAM_FILE

Where:

• $PARAM_FILE --> File which contains the paramter and values.
• IFS='=' Internal Field Separator. Parameter names and Values are separated by = sign. Example: appname=weblogic
• eval "$key='$value'" --> This will create system environment.

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Some Linux Console Fun

Try them out, if you are brave enough. :)

apt-get moo
apt-get install sl  
apt-get install furtune
apt-get install cowsay
apt-get install figlet

Examples:

sl

fortune | cowsay

figlet "Hello"

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Run command without X display

This method can be useful when you want to run a command (which needs X11 display), but X11 display isn't running on your system. Typical error message: failed to commit changes to dconf: Cannot autolaunch D-Bus without X11 $DISPLAY The solution is: xvfb-run

xvfb-run  -  run  specified  X  client or command in a virtual X server environment

Install:

apt-cache search xvfb-run
xvfb - Virtual Framebuffer 'fake' X server

apt-get install xvfb

How to use it?

xvfb-run --server-args="-screen 0, 1024x768x24" /usr/bin/ssconvert --export-type=Gnumeric_Excel:excel_dsf 20161105_090001.html 20161105_090001.xls

Or from a shell script:

xvfb-run --server-args="-screen 0, 1024x768x24" /usr/bin/wkhtmltopdf $*

There are 2 typical command I'm using with xvfb-run: ssconvert and wkhtmltopdf

Simple Image Viewer For Linux

feh -- image viewer and cataloguer

Failed To Install Cisco AnyConnect on Xubuntu 16.04

Error message: Failed to start vpnagentd.service: Unit vpnagentd.service not found.

Solution:

apt install network-manager-openconnect
systemctl daemon-reload

Then restart the install. REFERENCE:

https://technicalsanctuary.wordpress.com/2016/05/28/installing-cisco-anyconnect-vpn-on-ubuntu-16-04/

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Configure Extra Mouse Buttons Under Linux

This solution is tested on Linux Mint (Sarah) and Xubuntu 16.04. So I have a Logitech M505 mouse and I love using the vertical scroll button to minimize and maximize the active window. I have never used these buttons according to its original function, they were always configured to minimize and maximize Window.

What you need to install?

• xbindkeys
• xvkbd
• xdotool
• wmctrl

Install them with one command:

sudo apt install xbindkeys xvkbd xdotool wmctrl

Create sample configuration file

xbindkeys -d > ~/.xbindkeysrc

This will create a sample configuration file in your home directory.

Please remove the "Examples of commands:" section from this file to avoid furtherer conflicts.

"xbindkeys_show" 
  control+shift + q

Determine the ID of the buttons you want to use

It is very simple. Just run xev command.

For example my left button code (button 1):

ButtonPress event, serial 37, synthetic NO, window 0x4800001,
    root 0xc5, subw 0x0, time 7138218, (103,85), root:(965,1564),
    state 0x10, button 1, same_screen YES

ButtonRelease event, serial 37, synthetic NO, window 0x4800001,
    root 0xc5, subw 0x0, time 7138264, (103,85), root:(965,1564),
    state 0x110, button 1, same_screen YES

Example with grep to easier determine button ID:

xev | egrep -o 'button [0-9]{1,2}'

Configure .xbindkeysrc

So in my case I want to configure only two buttons:

• Left Scrolling for minimize window
• Right Scrolling for maximize window

I had to add only these two section to .xbindkeysrc:

• Minimize (Button 11)

"xdotool getactivewindow windowminimize"
b:11

* Maximize (button 12)

"wmctrl -r :ACTIVE: -b toggle,maximized_vert,maximized_horz"
b:12

As you can see we had to use two different command: xdotool and wmctrl.

If you want to use your buttons for any other activity I'm pretty sure that after some googleing you will find your solution.

Case Insensitive Search In Oracle DB

alter session set NLS_COMP=ANSI;
alter session set NLS_SORT=BINARY_CI;

REFERENCE:

http://stackoverflow.com/questions/1031844/oracle-db-how-can-i-write-query-ignoring-case

Change Date & Timestamp Format In Oracle DB

alter session set NLS_DATE_FORMAT='yyyy-mm-dd HH24:mi:ss';
ALTER SESSION SET NLS_TIMESTAMP_FORMAT='yyyy-mm-dd HH24:mi:ss';

Redirect all output (stderr, stdout) to a file

#!/bin/bash

LOG="[LOG file location]"
exec >> $LOG 2>&1
...
...
...

Redirect nohup output

You can redirect stdout and stderr to differrent files or into the same file.

Examples:

1. nohup ./program >stdout.log 2>stderr.log
2. nohup ./progrem >stoutAndStderr.log 2>&1
3. abbreviated syntax

nohup command > output-$(date +%Y%m%d_%H%M%S).log &

Example startup script for OpenHAB:

cat start-daemon.sh

#!/bin/sh
...
...
...

echo Launching the openHAB runtime...
nohup java \
    -Dosgi.clean=true \
    -Declipse.ignoreApp=true \
    -Dosgi.noShutdown=true  \
    -Djetty.port=$HTTP_PORT  \
    -Djetty.port.ssl=$HTTPS_PORT \
    -Djetty.home=.  \
    -Dlogback.configurationFile=configurations/logback.xml \
    -Dfelix.fileinstall.dir=addons -Dfelix.fileinstall.filter=.*\\.jar \
    -Djava.library.path=lib \
    -Djava.security.auth.login.config=/opt/openhab/runtime/distribution-1.8.3-runtime/etc/login.conf \
    -Dorg.quartz.properties=./etc/quartz.properties \
    -Dequinox.ds.block_timeout=240000 \
    -Dequinox.scr.waitTimeOnBlock=60000 \
    -Dfelix.fileinstall.active.level=4 \
    -Djava.awt.headless=true \
    -jar $cp $* \
    -console 9898 >nohup-$(date +%Y%m%d_%H%M%S).out &

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Last update: October 2, 2021