Posts Tagged ‘linux distros’

Ansible Quick Start Cheatsheet for Linux admins and DevOps engineers

Wednesday, October 24th, 2018

ansible-quick-start-cheetsheet-ansible-logo

Ansible is widely used (Configuration management, deployment, and task execution system) nowadays for mass service depoyments on multiple servers and Clustered environments like, Kubernetes clusters (with multiple pods replicas) virtual swarms running XEN / IPKVM virtualization hosting multiple nodes etc. .

Ansible can be used to configure or deploy GNU / Linux tools and services such as Apache / Squid / Nginx / MySQL / PostgreSQL. etc. It is pretty much like Puppet (server / services lifecycle management) tool , except its less-complecated to start with makes it often a choose as a tool for mass deployment (devops) automation.

Ansible is used for multi-node deployments and remote-task execution on group of servers, the big pro of it it does all its stuff over simple SSH on the remote nodes (servers) and does not require extra services or listening daemons like with Puppet. It combined with Docker containerization is used very much for later deploying later on inside Cloud environments such as Amazon AWS / Google Cloud Platform / SAP HANA / OpenStack etc.

Ansible-Architechture-What-Is-Ansible-Edureka

0. Instaling ansible on Debian / Ubuntu Linux


Ansible is a python script and because of that depends heavily on python so to make it running, you will need to have a working python installed on local and remote servers.

Ansible is as easy to install as running the apt cmd:

# apt-get install –yes ansible
 

The following additional packages will be installed:
  ieee-data python-jinja2 python-kerberos python-markupsafe python-netaddr python-paramiko python-selinux python-xmltodict python-yaml
Suggested packages:
  sshpass python-jinja2-doc ipython python-netaddr-docs python-gssapi
Recommended packages:
  python-winrm
The following NEW packages will be installed:
  ansible ieee-data python-jinja2 python-kerberos python-markupsafe python-netaddr python-paramiko python-selinux python-xmltodict python-yaml
0 upgraded, 10 newly installed, 0 to remove and 1 not upgraded.
Need to get 3,413 kB of archives.
After this operation, 22.8 MB of additional disk space will be used.

apt-get install –yes sshpass

Installing Ansible on Fedora Linux is done with:

# dnf install ansible –yes sshpass

On CentOS to install:
 

# yum install ansible –yes sshpass

sshpass needs to be installed only if you plan to use ssh password prompt authentication with ansible.

Ansible is also installable via python-pip tool, if you need to install a specific version of ansible you have to use it instead, the package is available as an installable package on most linux distros.

Ansible has a lot of pros and cons and there are multiple articles already written on people for and against it in favour of Chef or Puppet As I recently started learning Ansible. The most important thing to know about Ansible is though many of the things can be done directly using a simple command line, the tool is planned for remote installing of server services using a specially prepared .yaml format configuration files. The power of Ansible comes of the use of Ansible Playbooks which are yaml scripts that tells ansible how to do its activities step by step on remote server. In this article, I'm giving a quick cheat sheet to start quickly with it.
 

1. Remote commands execution with Ansible
 

First thing to do to start with it is to add the desired hostnames ansible will operate with it can be done either globally (if you have a number of remote nodes) to deploy stuff periodically by using /etc/ansible/hosts or use a custom host script for each and every ansible custom scripts developed.

a. Ansible main config files

A common ansible /etc/ansible/hosts definition looks something like that:

# cat /etc/ansible/hosts
[mysqldb]
10.69.2.185
10.69.2.186
[master]
10.69.2.181
[slave]
10.69.2.187
[db-servers]
10.69.2.181
10.69.2.187
[squid]
10.69.2.184

Host to execute on can be also provided via a shell variable $ANSIBLE_HOSTS
b) is remote hosts reachable / execute commands on all remote host

To test whether hour hosts are properly configure from /etc/ansible/hosts you can ping all defined hosts with:

ansible all -m ping


ansible-check-hosts-ping-command-screenshot

This makes ansible try to remote to remote hosts (if you have properly configured SSH public key authorization) the command should return success statuses on every host.

ansible all -a "ifconfig -a"


If you don't have SSH keys configured you can also authenticate with an argument (assuming) all hosts are configured with same password with:

ansible all –ask-pass -a "ip all show" -u hipo –ask-pass


ansible-show-ips-ip-a-command-screenshot-linux

If you have configured group of hosts via hosts file you can also run certain commands on just a certain host group, like so:

ansible <host-group> -a <command>

It is a good idea to always check /etc/ansible/ansible.cfg which is the system global (main red ansible config file).

c) List defined host groups
 

ansible localhost -m debug -a 'var=groups.keys()'
ansible localhost -m debug -a 'var=groups'

d) Searching remote server variables

# Search remote server variables
ansible localhost -m setup -a 'filter=*ipv4*'

ansible localhost -m setup -a 'filter=ansible_domain'

ansible all -m setup -a 'filter=ansible_domain'

# uninstall package on RPM based distros
ansible centos -s -m yum -a "name=telnet state=absent"
# uninstall package on APT distro
ansible localhost -s -m apt -a "name=telnet state=absent"

2. Debugging – Listing information about remote hosts (facts) and state of a host

# All facts for one host
ansible -m setup
  # Only ansible fact for one host
ansible
-m setup -a 'filter=ansible_eth*'
# Only facter facts but for all hosts
ansible all -m setup -a 'filter=facter_*'


To Save outputted information per-host in separate files in lets say ~/ansible/host_facts

ansible all -m setup –tree ~/ansible/host_facts

3. Playing with Playbooks deployment scripts

a) Syntax Check of a playbook yaml

ansible-playbook –syntax-check


b) Run General Infos about a playbook such as get what a playbook would do on remote hosts (tasks to run) and list-hosts defined for a playbook (like above pinging).

ansible-playbook –list-hosts
ansible-playbook
–list-tasks


To get the idea about what an yaml playbook looks like, here is example from official ansible docs, that deploys on remote defined hosts a simple Apache webserver.
 


– hosts: webservers
  vars:
    http_port: 80
    max_clients: 200
  remote_user: root
  tasks:
  – name: ensure apache is at the latest version
    yum:
      name: httpd
      state: latest
  – name: write the apache config file
    template:
      src: /srv/httpd.j2
      dest: /etc/httpd.conf
    notify:
    – restart apache
  – name: ensure apache is running
    service:
      name: httpd
      state: started
  handlers:
    – name: restart apache
      service:
        name: httpd
        state: restarted

To give it a quick try save the file as webserver.yml and give it a run via ansible-playbook command
 

ansible-playbook -s playbooks/webserver.yml

The -s option instructs ansible to run play on remote server with super user (root) privileges.

The power of ansible is its modules, which are constantly growing over time a complete set of Ansible supported modules is in its official documenation.

Ansible-running-playbook-Commands-Task-script-Successful-output-1024x536

There is a lot of things to say about playbooks, just to give the brief they have there own language like a  templates, tasks, handlers, a playbook could have one or multiple plays inside (for instance instructions for deployment of one or more services).

The downsides of playbooks are they're so hard to write from scratch and edit, because yaml syntaxing is much more stricter than a normal oldschool sysadmin configuration file.
I've stucked with problems with modifying and writting .yaml files and I should say the community in #ansible in irc.freenode.net was very helpful to help me debug the obscure errors.

yamllint (The YAML Linter tool) comes handy at times, when facing yaml syntax errors, to use it install via apt:
 

# apt-get install –yes yamllint


a) Running ansible in "dry mode" just show what ansible might do but not change anything
 

ansible-playbook playbooks/PLAYBOOK_NAME.yml –check


b) Running playbook with different users and separate SSH keys

ansible-playbook playbooks/your_playbook.yml –user ansible-user
 
ansible -m ping hosts –private-key=~/.ssh/keys/custom_id_rsa -u centos

c) Running ansible playbook only for certain hostnames part of a bigger host group

ansible-playbook playbooks/PLAYBOOK_NAME.yml –limit "host1,host2,host3"


d) Run Ansible on remote hosts in parallel

To run in raw of 10 hosts in parallel
 

# Run 10 hosts parallel
ansible-playbook <File.yaml> -f 10            


e) Passing variables to .yaml scripts using commandline

Ansible has ability to pre-define variables from .yml playbooks. This variables later can be passed from shell cli, here is an example:

# Example of variable substitution pass from command line the var in varsubsts.yaml if present is defined / replaced ansible-playbook playbooks/varsubst.yaml –extra-vars "myhosts=localhost gather=yes pkg=telnet"

 

4. Ansible Galaxy (A Docker Hub) like large repository with playbook (script) files

Ansible Galaxy has about 10000 active users which are contributing ansible automation playbooks in fields such as Development / Networking / Cloud / Monitoring / Database / Web / Security etc.

To install from ansible galaxy use ansible-galaxy

# install from galaxy the geerlingguy mysql playbook
ansible-galaxy install geerlingguy.mysql


The available packages you can use as a template for your purpose are not so much as with Puppet as Ansible is younger and not corporate supported like Puppet, anyhow they are a lot and does cover most basic sysadmin needs for mass deployments, besides there are plenty of other unofficial yaml ansible scripts in various github repos.

Preventing packages on Debian and Ubuntu Linux to not update on system updates

Wednesday, March 6th, 2013

On Debian based GNU / Linux distros, there are some critical packages which need to be disabled to update during the common routine apt-get update && apt-get upgrade which is a almost daily part of Debian sysadmin living. Example for packages which are good to mark not to upgrade are for example; linux kernel, java virtual machine, adobe flash plugin,  etc.

Setting a package to omit upgrade on system package update for adobe flash plugin for example is with:

# echo adobe-flashplugin hold | dpkg –set-selections
debian:~# echo adobe-flash-properties-gtk hold | dpkg --set-selections
debian:~# echo flashplugin-nonfree-extrasound hold | dpkg --set-selections

To do deb package update on hold for kernel;

debian:~# echo linux-image-generic hold | dpkg --set-selections
debian:~# echo linux-image-3.2.0-38-generic | dpkg --set-selections

Do the same for as many packages which seem to break up on updates and when, you explicitly want remove the hold/s run:

debian:~# echo adobe-flashplugin install | dpkg --set-selections
....
debian:~# echo linux-image-generic install | dpkg --set-selections

Viewing JPEG,GIF and PNG in ASCII with cacaview on GNU / Linux – Review on caca-utils text mode graphics utilities

Thursday, May 17th, 2012

Stitch 80x45 libcaca mascot cacaview viewing JPG, PNG, GIF images as ASCII on Linux libcaca

Probably, many don't know that it is possible to view normal graphical pictures (JPG, PNG, GIF, BMP) etc. in plain console tty.

Being able to view pictures in ASCII is something really nice especially for console geeks like me.
The images produced sometimes are a bit unreadable, if compared to the original graphics, but anyways most of the pictures looks pretty decent 🙂

Viewing in console / terminal images on GNU / Linux is possible thanks to a library called libcaca, caca labs libcaca project official website here.
Below is a shot description of libcaca:
hipo@noah:~$ apt-cache show libcaca0|grep 'Description' -A 4
Description: colour ASCII art library
libcaca is the Colour AsCii Art library. It provides high level functions
for colour text drawing, simple primitives for line, polygon and ellipse
drawing, as well as powerful image to text conversion routines.

In Debian, Ubuntu and other deb Linux distros viewing GUI images with no need for Xserver or any kind of window manager in plain ASCII is possible with cacaview.

cacaview is part of a package called caca-utils. caca-utils is providing few other great utilities for ASCII freaks 🙂 along with cacaview console ascii viewer prog.
The package> is available for Debian distributins since many years, so even on a very old Debians like Debian – (Potato, Woody, Sarge) the package is available in default free package repositories ready to install via apt

To install apt-get it as usual:

noah:~# apt-get --yes install caca-utils

Here is a list of the binaries the package provides:

hipo@noah:~$ dpkg -L caca-utils|grep -i /usr/bin/
/usr/bin/cacaserver
/usr/bin/cacaplay
/usr/bin/cacafire
/usr/bin/cacademo
/usr/bin/cacaview
/usr/bin/img2txt

1. cacaserver a tiny program allowing network streaming of applications written in caca

Belkow is a chop, from man cacaserver
 

cacaserver reads libcaca animation files in its standard input and
serves them as ANSI art on network port 51914. These animations can be
created by any libcaca program by setting the CACA_DRIVER environment
variable to raw and piping the program's standard output to cacaserver.

Clients can then connect to port 51914 using telnet or netcat to see
the output.

The example section of the manual points 1 example use of cacaserver to stream the console output from cacademo.
cacademo binary is a short presentation ASCII DEMO in the spirit of the old school assembly demos (demoscene) .
To run it to bind on port 51914 one has to type in bash shell:
hipo@noah:~$ CACA_DRIVER=raw cacademo | cacaserver
initialised network, listening on port 51914

Then to check out how the demo looks, open telnet connection to the cacaserver host; In my case the cacaserver is binded and streamed over IP 192.168.0.2:

hipo@debian:~$ telnet 192.168.0.2 51914

Immediately you got the demo shining; Below are two screenshots of the demo played after succesful telnet connection:

Cacaserver - caca for the network screenshot Matrix cacademo

cacademo running over telnet network connection – Matrix

cacaserver running on Debian GNU / Linux drug addict like spots streamed via telnet

Blur spots cacademo shot of cacademo streamed via network

You see the demo looks quite awesome 🙂

2. Running cacafire to stream over network

Another possible example use of cacaserver is in conjunction with cacafire libcaca test application:

noah:~# CACA_DRIVER=raw cacafire | cacaserver
initialised network, listening on port 51914
cacafire is a short application written to render ASCII via libcaca and is just displaying a screen with ASCII (moving) burning fire.
It is quite spectacular if you, ask an unexpecting friend to connect to your host to 51914 🙂

Cacafire Screenshot Debian GNU / Linux cacaserver streaming ASCII demo via network port 51914

Besides that bored sys admins, could run cacafire in console to hypnotize themselves watching dumb the burning fire screen for few hoursor just use it as a screensaver 😉

3. cacaview a program to display a graphic images in console using ASCII art

cacaview takes just one argument – the picture to be displayed.

Below is a screenshot of cacaview ran from my gnome-terminal displaying a ASCII text version of the MySQL server logo

hipo@noah:~$ cd /disk/pictures
hipo@noah:/disk/pictures$ cacaview mysql_logo.png

 

cacaview displaying MySQL database logo in ASCII using caca for X

Whether cacaview is invoked in GUI, the libcaca X support is used, so the text image is visualized in new window with graphics, if however it is invoked in plain let's say tty1 libcaca displays the graphics pictures drawing it with only text characters.

Here is also a screenshot, I've made while viewing a GIF website logo in ASCII in plain tty console:

hipo@noah:~$ cacaview /disk/pictures/logo.gif

cacaview plain tty console screenshot of a website logo graphics pictures 17-05-2012

The logo is in cyrillic, so for latin speaking people some of the characters in the two words seen will be unreadable 🙂

cacaview even supports viewing, the next and previous picture in line, like in any modern graphics image viewer program.
To view a bunch of graphic pictures in ASCII with cacaview pass it *.*:

hipo@noah:~$ cacaview /disk/pictures/*.*

For simplicity the common unix * is also supported, so I find it quicker to do:

hipo@noah:~$ cacaview /disk/pictures/*

Showing pictures forward and backward (Previous / Next) picture is done with n and p kbd keys, whether;
n - next;
p - previous

cacaview doesn't crash or stop but skip unknown file formats – if for instance encounters filenames which are not images; lets say you have *.rar archive files along with other pictures.

The complete list of keys cacaview supports are:
br />

KEYS
? show the help screen

n, p switch to next image, previous image

Left, Right, Up, Down or h, l, k, j
scroll the image around

+, – zoom in and out

z reset the zoom level to normal

f switch fullscreen mode (hide/show menu and status bars)

d toggle the dithering mode (no dithering, 4×4 ordered dithering, 8×8 ordered dithering and random dithering)

q exit the program

4. Converting graphics images to ASCII art like (plain text pictures)

The tool that does "the trick" is img2txt. img2txt has a bit more options while compared to the rest of the aforementioned tools.The following list of arguments are recognized:

  • the size (font, height)
  • brightness
  • contrast
  • gamma and dither
  • format type of out the output pic

Anyways I found that the basic just in / out arguments passed are enough to produce pretty good results:

hipo@noah:~$ img2txt hipo_avatar.gif >hipo_avatar_pic.txt

The original hipo_avatar.gif file looks like so:

hipo avatar gif picture before img2txt convertion to text

After above img2txt command is run and hipo_avatar_pic.txt to see the colorful output ASCII art img2txt produces, cat it:

hipo@noah:~$ cat hipo_avatar_pic.txt

The image result if screenshot looks quite beautiful and even, can be considered or used as an ART effect image (filter) 🙂

Console Screenshot hipo avatar pic ASCII img2txt output picture

The picture colors are plain ANSI color, so in order to display properly the picture with colors on another computers or Operating System you will need at least basic support for ANSI colors.

Plenty of output file formats are supported by img2txt

Here is the complete list of supported output formats:
 

ansi : coloured ANSI
caca : internal libcaca format
utf8 : UTF8 with CR
utf8 : UTF8 with CRLF (MS Windows)
html : HTML with CSS and DIV support
html3 : Pure HTML3 with tables
irc : IRC with ctrl-k codes
bbfr : BBCode (French)
ps : Postscript
svg : Scalable Vector Graphics
tga : Targa Image

libcaca is available for FreeBSD too, but the caca-utils is not available as a port yet, though probably the deb or rpm packages can easily be ported to BSD.

Well that's all, Enjoy.

Installing Linux on old hardware PC. Few thoughs on Puppy and Xubuntu Linux

Tuesday, January 24th, 2012

I needed a G/Linux distribution that will work fine on an old PC with hardware configuration:

guest@xubuntu-desktop:~$ grep -i cpu /proc/cpuinfo; free -m; df -h
cpu family : 6
cpu MHz : 797.613cpuid level : 2
total used free shared buffers cachedMem: 497 470 26 0 35 259-/+ buffers/cache: 176 321Swap: 1454 10 1444File System Size Used Free % Mounted on
/dev/sda1 37G 4,3G 31G 13% /

I've read a lot on the internet and come to the conclusion I have basicly two popular Linux distros as option to install on archaic x86 hardware:

1. Puppy Linux
2. Xubuntu Linux

I first give Puppy Linux a try. It worked quite nice, but the interface was too old school and the desktop felt like a bit out-dated.
Besides that many of the Puppy Linux shipped programs were not a mainstream programs available across most of the other Linux distributions.

Many of the programs shipped with Puppy are great, but more suitable for a computer geek than for a Windows accustomed GUI user.
Puppy Linux Screenshot

My opinion on Puppy (from what I've seen) is that its great distro for old school hardcore Linux users.
Anyways its not suitable for absolutely "uniniated" users who encounter Linux for a first time.

Secondly I installed Xubuntu. Most of the archaic hardware on the PC was detected during install time (a pleasently surprise).
Xubunto works fast and Xfce menus opens "light fast" as on the old 800Mhz pc with 512 mem of ram. Generally the GUI worked quick and responsive.
To conclude I liked Xubuntu a lot and I strongly recommend it to anyone who want to quickly roll on Linux on an old PC.
Xubuntu GNU / Linux theme

What impressed me most is the minimalistic look & feel and simplicity.

I'm sure Debian will be working great on old hardware as well, however configuring it will be hell a lot of work. Thus I think Xubuntu is a good choice for people who want save some time in obscure configurations and easily have a neat Linux ready for desktop use.