Laura Liparulo's blog

Tag: linux

Docker commands – Getting started

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Posted inCONTAINERS

To run one of the Docker official image, you can simply use “docker run”:

$ docker run centos

The first time you run it, the image can´t be found and must be downloaded:

Once downloaded, the image is saved in the docker cache and can be reused if necessary.

If it´s an official image, you would only need to enter the image name only.

But it´s taken from a user´s repo the format is: <username>/<image>.

The 100% Free software linux image Trisquel, for example, is taken from the repository of a user called “kpengboy“.

In this case, even if you are logged in, you can´t run “docker run”. You need to pull it first:

$docker pull kpengboy/trisquelbash

To see the list of the images donwload so far, run:

$ docker images

If you also want to start a bash in the container, use “-it” for the interactive mode:

$ docker run -it kpengboy/trisquel

Then you can work with the bash shell:

As default, docker will download the latest version available, but you can additionally specify a version (called “tag”) you want to work with:

$ docker run redis:4.0

If you want to access a webapp or, for example, a database, you generally get an assigned url with a port number. But you can change the ports, by adding them as parameters.

For example, if you want to run mysql and access it at a different port than 3306, use the “-p” option to give <host>:<container-port>:

$ docker run  -p 52000:3307 mysql

To persist your data, even when the container is killed, you can mount a persistent volume with “-v”:

$ docker run -v /opt/data/mysql mysql

You can pass an environment variable to you container, which might help you to avoid modifying the image and achieve some strategic solution:

$ docker run -e BACKGROUND_COLOR simple-web-app

To see which containers are running:

$ docker ps

To see the stopped containers to

$ docker ps -a

If you want to get the details of a specific container:

$ docker inspect vibrant_chatelet

You can check the log by running:

$ docker logs vibrant_chatelet

You can start a container in background mode with the “-d” option:

$ docker -d kpengboy/trisquel

To remove a container (even if it´s running)

$ docker rm vibrant_chatelet

Or by containerID

$ docker rm 0d6d64f9053c

To remove the image you need to make sure that no container is running it first. You migh use “docker stop” or just remove it directly.

To remove an image you need:

$ docker rmi kpengboy/trisquel

Kubernetes – Resources limits

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Posted incloud , CONTAINERS , Kubernetes

As containers might be consuming too many compressible resources, such as CPU or network bandwidth. And also incompressible resources, like memory.

Luckily, Kubernetes can access and control the linux cgroups CPU and memory limitations for each pod.

Kubernetes distinguish between “requests” and “limits”, very much like soft/hard limits in linux.

Requests specify the minimum amount of resources that are needed, whereas limits define the maximum amount the containers can grow up to. This means that limits are supposed to be larger than the requests.

The kubernetes schedules assings a pod to a node according to the requests value: only the nodes that can have enough capacity to accomodate the pods are considered for scheduling.

So, basically, the requests sections determines where a Pod will be scheduled.

HOW TO CONFIGURE RESOURCES

You can add the specification to your deployment or pod (?) directly with the “set” command:

$ kubectl set resources deployment nginx --limits=cpu=200m,memory=512Mi --requests=cpu=100m,memory=256Mi

This will awork as a live update and will assign the same values to each container in your deployment.

Your pods will be recreated with the new values.

Resources are always defined in the container section:

apiVersion: v1
kind: Pod
metadata:
  name: random-generator
spec:
  containers:
  - image: k8spatterns/random-generator:1.0
    name: random-generator
    resources:
      requests:                         
        cpu: 100m
        memory: 100Mi
      limits:                           
        cpu: 200m
        memory: 200Mi

If you omit the resources configuration, default values will be added.

In this case a best-effort strategy will be put in place, which means the pods will have the lowest priority and be killed first, where the node runs out of resources.

You won´t see any entry in the yaml manifest:

Convert audiofiles on Ubuntu by the command line with soundconverter

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Posted inLinux , Programming , shell

If you need to convert audio files in another format you can use the tool called “soundconverter”, that you can simply install:

~$ sudo apt-get install soundconverter

Then simply run a command like:

~$ soundconverter -b -m "audio/mpeg" -s ".mp3" /home/laura/cd-wav/*.wav

“-b” stands for batch type

“-m” to specify the mime format.

“-s” to specify the suffix

And move them into another folder eventually:

~$ mv /home/laura/cd-irene/*.mp3 /home/laura/cd-wav.

For more info check the official wiki pages:
http://wiki.ubuntuusers.de/soundconverter
http://manpages.ubuntu.com/manpages/karmic/man1/soundconverter.1.html

Linux file system

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Posted inLinux

filesystem: the files and directories (or folders), the method used to store data on the hard drive (such as the ext3 filesystem.

– Windows keeps all the important system files in a single directory C:\
– Linux follows the lead of its UNIX
– Windows and Linux setups are both logical

✓ Linux uses a forward slash (/) between directories, not the backslash (\) that Windows uses. So, the file yum.conf in the directory etc is
etc/yum.conf.

✓ Files and directories can have names up to 256 characters long, and these names can contain underscores (_), dashes (-), and dots (.) any-
where within. So my.big.file or my.big_file or my-big-file are all valid filenames.

✓ Upper- and lowercase matter. They have to match exactly. The files yum.conf and Yum.conf are not the same as far as Linux is concerned.
Linux is case-sensitive — it pays attention to the case of each character. Windows, on the other hand, is case-insensitive.

✓ The same filesystem can span multiple partitions, hard drives, and media (such as CD-ROM drives). You just keep going down through
subdirectories, not having to care whether something is on disk A, B, or whatever.

Everything in the Linux filesystem is relative to the root directory — not to be confused with the system Administrator, who is the root user. The root directory is referred to as /, and it is the filesystem’s home base — a doorway into all your files. As such, it contains a relatively predictable set of subdirectories. Each distribution varies slightly in terms of what it puts in the root directory. More or less you can find the following directories.

/bin   : Essential commands that everyone needs to use at any time.*
/boot  : The information that boots the machine, including your kernel.*
/dev :  The device drivers for all the hardware that your system needs to  interface with.*
/etc  : The configuration files for your system.*
/home  : The home directories for each of your users.
/lib  : The libraries, or the code that many programs (and the kernel) use.*
/media  : A spot where you add temporary media, such as floppy disks and  CD-ROMs; not all distributions have this directory.
/mnt  :  A spot where you add extra filesystem components such as networked drives and items you aren’t permanently adding to your filesystem but that aren’t as temporary as CD-ROMs and floppies.
/opt   : The location that some people decide to use (and some programs want to use) for installing new software packages, such as word
processors and office suites.
/proc   : Current settings for your kernel (operating system).*
/root   : The superuser’s (root user’s) home directory.
/sbin   : The commands the system Administrator needs access to.*
/srv   : Data for your system’s services (the programs that run in thebackground).*
/sys   : Kernel information about your hardware.*
/tmp   : The place where everyone and everything stores temporary files.
/usr   : A complex hierarchy of additional programs and files.
/var   : The data that changes frequently, such as log files and your mail.

Most common linux file extensions

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Posted inLinux

There is no .exe equivalent in linux. Executables are denoted by file permissions, not extensions. In directories such as /etc, many files do not use a file extension because it is in /etc it is assumed to be a configuration (ASCII text) file.

Ex. “RELEASE NOTE” is the correct name for a file (remember that it’s case sensitive).

The following list shows the most commons file extensions for linux:

.a   : a static library ;
.au    : an audio file ;
.bin :    a) a binary image of a CD (usually a .cue file is also included); b) represents that the file is binary and is meant to be executed ;
.bz2 :    A file compressed using bzip2 ;
.c :    A C source file ;
.conf :  A configuration file. System-wide config files reside in /etc while any user-specific configuration will be somewhere in the user’s home directory ;
.cpp :  A C++ source file ;
.deb :  a Debian Package;
.diff :   A file containing instructions to apply a patch from a base version to another version of a single file or a project (such as the linux kernel);
.dsc:   a Debian Source information file ;
.ebuild : Bash script used to install programs through the portage system. Especially prevalent on Gentoo systems;
.el :  Emacs Lisp code file;
.elc :  Compiled Emacs Lisp code file;
.gif :    a graphical or image file;
.h :a C or C++ program language header file;
.html/.htm  :   an HTML file;
.iso :    A image (copy) of a CD-ROM or DVD in the ISO-9660 filesystem format;
.jpg :    a graphical or image file, such as a photo or artwork;
.ko :    The kernel module extension for the 2.6.x series kernel;
.la :    A file created by libtool to aide in using the library;
.lo :    The intermediate file of a library that is being compiled;
.lock :    A lock file that prevents the use of another file;
.log :    a system or program’s log file;
.m4 :    M4 macro code file;
.o :    1) The intermediate file of a program that is being compiled ; 2) The kernel module extension for a 2.4 series kernel ; 3)a program object file;
.pdf :    an electronic image of a document;
.php :     a PHP script;
.pid :    Some programs write their process ID into a file with this extention;
.pl :    a Perl script;
.png :    a graphical or image file;
.ps :    a PostScript file; formatted for printing;
.py :    a Python script;
.rpm :    an rpm package. See Distributions of Linux for a list of distributions that use rpms as a part of their package management system;
.s :    An assembly source code file;
.sh :    a shell script;
.so :     a Shared Object, which is a shared library. This is the equivalent form of a Windows DLL file;
.src  :    A source code file. Written in plain text, a source file must be compiled to be used;
.sfs :    Squashfs filesystem used in the SFS Technology;
.tar.bz2 , tbz2, tar.gz :     a compressed file per File Compression;
.tcl :    a TCL script;
.tgz :     a compressed file per File Compression. his may also denote a Slackware binary or source package;
.txt :    a plain ASCII text file;
.xbm :    an XWindows Bitmap image;
.xpm :     an image file;
.xcf.gz, xcf :  A GIMP image (native image format of the GIMP);
.xwd :    a screenshot or image of a window taken with xwd;
.zip :extension for files in ZIP format, a popular file compression format;
.wav :    an audio file.

Sqlite database backup: the .dump command

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Posted inLinux , Programming , SQL

Let’s go on mastering our sqlite3 knowledge.
SQLite database is really just a file: a backup it’s as simple as copying one file.

The .dump command shows information about all the changes performed onto the database. Less pieces of information to the hidden file can be found in your home/user typing: $ ~/.sqlite_history.

$ sqlite3 test.db “.dump”

The result is:
PRAGMA foreign_keys=OFF;
BEGIN TRANSACTION;
CREATE TABLE n(id INTEGER PRIMARY KEY, f TEXT, l TEXT);
INSERT INTO “n” VALUES(1,’linus’,’torvalds’);
INSERT INTO “n” VALUES(2,’richard’,’stallman’);
COMMIT;

If you want to backup the database in a new file, you can specify a name (ex. “dbbackup”):
$ $ sqlite3 test.db ‘.dump’ > dbbackup

The contents of the backup can be modified.
For example you can filter and pipe it to another database. Below, table “n” is changed to “people” with the sed command, and it is piped into the “computer_pioneers” database.

$ sqlite3 test.db “.dump”|sed -e s/n/people/|sqlite3 computer_pioneers.db
The contect is the same:
$sqlite3 computer_pioneers.db “select * from people”;

First steps in Sqlite and Perl

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Posted inLinux , Programming , SQL

Sqlite is useful to create a database (one file, .db extension) used to store configuration data, used Miicrosoft, Skype, Banshee… Smart Phone applications….

The file extension .db stands for a whole database: it’s made by the software C library called Sqlite…

This is a great opportunity to learn about SQLITE and the Perl scripting languages… great, don’t you think?
Let’s kill two birds with a stone!
Install Sqlite3 and follow me:
On UBUNTU, DEBIAN, etc:
$ sudo apt-get install sqlite3
On OPEN-SUSE:
$ sudo zypper install sqlite3
On REDHAT, CentOS, or FEDORA:
$ yum install SQLite3

BASH EXAMPLE
Let’s create an example: a database called “test.db” by the (unix) shell by the following command:

:~$ sqlite3 test.db “create table if not exists user(id INTEGER PRIMARY KEY, name TEXT,  surname TEXT);”

Let’s fill it:
:~$ sqlite3 test.db “insert into user (name, surname) values (‘linus’,’torvalds’);”

:~$ sqlite3 test.db “insert into user(name,surname) values(‘richard’, ‘stallman’)”;

To check it out:
:~$sqlite3 test.db “select * from n”;

The result is:
1|linus|torvalds
2|richard|stallman

Alternatively you can create a database entering the sqlite3 enviroment
$ sqlite3 test.db
SQLite version 3.0.8
Enter “.help” for instructions
Enter SQL statements terminated with a “;”
sqlite>

In the sqlite3 enviroment you can use pure SQL statements to work with your database (in this case the test.db).
You can even change a few default settings to make the ouput of the commands look better. For example the column .mode and the .headers commands.They will last you exit the SQLite shell or change them to something else.
sqlite> .mode col
sqlite> .headers on

To see all the tables and views type:
sqlite> .tables

To see the databases that are currently open use the .databases command. It will show the main and temp databases and where they are on the system:
sqlite> .databases

To exit type .quit or .exit:
sqlite> .quit

Anyway it’s better to work in the shell prompt directly, that allows you to run bash scripts.
In this example the prompt is in your home/user directory. Check it out by the pwd command if you’re not sure…

PERL EXAMPLE

Make a file called test.pl :
$ touch test1.pl

Use an editor(ex. gedit under ubuntu and opensuse) or the cat test1.pl command to fill it with the following script:


#!/usr/bin/perl -w

use DBI;
use strict;

my $db = DBI->connect(“dbi:SQLite:test.db”, “”, “”) or die “couldn’t connect to db”.DBI->errstr;

$db->do(“CREATE TABLE IF NOT EXISTS user (id INTEGER PRIMARY KEY, name TEXT, surname TEXT)”);
$db->do(“INSERT INTO user\(name, surname) VALUES ( ‘linus’, ‘torvalds’)”);
$db->do(“INSERT INTO user\(name, surname) VALUES ( ‘richard’, ‘stallman’)”);

my $all = $db->selectall_arrayref(“SELECT * FROM USER”);

foreach my $row (@$all) {
my ($id, $name, $surname) = @$row;
print “$id|$name|$surname \n”;

}

$db->disconnect;

Alternatively you can make the file directly by the shell:
$ cat > test.pl
.. perl script content…

Type Ctlr+C to close the file and exit.
Now check the file content:
$> cat test.pl

Make the perl script executable:
$ sudo chmod +x test.pl
Then run the perl script simply:
$ ./test.pl
The result is:
1|linus|torvalds
2|richard|stallman

In the same folder where the script lies, you can find a file called “test.db”. That’s the Sqlite database. Just one file.

Yeah! So we’ve learned some Perl and SQLite, right?

Discovering Sqlite by Banshee media player

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Posted inLinux , News

Banshee is the standard media player software in Ubuntu 11.04 and OpenSuse 11.4.

It’s a cross-platform application, but it’s basically currently running on “unixoide” operative systems only.

It’s written in C# and and it’s build upon Mono and GTK+ (GIMP Toolkit) and the GStreamer frawework, that is used to create media handling components like audio and video playback, recording, streaming and editing.

With Banshee you can  play music, videos and webradios,  import and put media on your Android, Apple, or other player — or import from it. You can even purchase music from the integrated Amazon MP3 Store.

As I have a subscriptio to LinuxMagazin (german version), I’ve found a very interesting article about it. Even a mini-tutorial online: http://www.linux-magazin.de/plus/2011/06/Perl-Snapshot-Linux-Magazin-2011-06

So I’ve just discovered that in the hidden folder  .config/banshee-1/ you can find the file called “banshee.db”.

The extension .db stands for a whole database: it’s made by the software C library called Sqlite…

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