About Asher256

GitHub: http://github.com/Asher256

Puppet module to configure LizardFS (Distributed File System) on Linux

Posted on February 24, 2017 by Asher256

I published recently the Puppet module puppet-lizardfs (give me a star on Github to encourage the project!) you can use to configure LizardFS, a highly-available distributed file system (DFS). LizardFS makes files secure by keeping all data in many replicas spread over several Linux servers.

The Puppet module puppet-lizardfs is an open source project, and community contributions are essential for keeping it great. I encourage you to contribute. Send me your pull requests on Github! Currently, Debian and CentOS/RedHat are supported.

A Puppet example: Continue reading →

3 advices to write robust Bash scripts

Posted on May 25, 2016 by Asher256

To write robust Bash scripts, I recommend you to:

1. Activate the Bash options: errexit, nounset

Add these two options at the top of your BASH scripts:

#!/usr/bin/env bash
set -o errexit      
set -o nounset

#!/usr/bin/env bash

set -o errexit

set -o nounset

errexit will stop your Bash script each time a command in your script returns an exit code different than “0”. It does not show any message when it quits, this is why it is important to show a traceback (check the second advice below “show a Bash traceback”).
nounset will stop your script and output an error if you attempt to use undefined variables. nounset is very important because it can avoid you to run dangerous commands like: rm –fr “/$undefinedvariable”

2. Show a Bash Traceback

Because the option “errexit” does not show any message when it stops your Bash script in some cases (for example var=$(yourcommand) will exit without any message, even when yourcommand returns an exit code different than zero), I recommend you to add the code below to show a traceback each time “errexit” forces your Bash script to stop:

#!/usr/bin/env bash

set -o errexit    # stop the script each time a command fails
set -o nounset    # stop if you attempt to use an undef variable

function bash_traceback() {
  local lasterr="$?"
  set +o xtrace
  local code="-1"
  local bash_command=${BASH_COMMAND}
  echo "Error in ${BASH_SOURCE[1]}:${BASH_LINENO[0]} ('$bash_command' exited with status $lasterr)"
  if [ ${#FUNCNAME[@]} -gt 2 ]; then
    # Print out the stack trace described by $function_stack
    echo "Traceback of ${BASH_SOURCE[1]} (most recent call last):"
    for ((i=0; i < ${#FUNCNAME[@]} - 1; i++)); do
    local funcname="${FUNCNAME[$i]}"
    [ "$i" -eq "0" ] && funcname=$bash_command
    echo -e "  $i: ${BASH_SOURCE[$i+1]}:${BASH_LINENO[$i]}\t$funcname"
    done
  fi
  echo "Exiting with status ${code}"
  exit "${code}"
}

# provide an error handler whenever a command exits nonzero
trap 'bash_traceback' ERR

# propagate ERR trap handler functions, expansions and subshells
set -o errtrace

#!/usr/bin/env bash

set -o errexit # stop the script each time a command fails

set -o nounset # stop if you attempt to use an undef variable

function bash_traceback() {

local lasterr="$?"

set +o xtrace

local code="-1"

local bash_command=${BASH_COMMAND}

echo "Error in ${BASH_SOURCE[1]}:${BASH_LINENO[0]} ('$bash_command' exited with status $lasterr)"

if [ ${#FUNCNAME[@]} -gt 2 ]; then

# Print out the stack trace described by $function_stack

echo "Traceback of ${BASH_SOURCE[1]} (most recent call last):"

for ((i=0; i < ${#FUNCNAME[@]} - 1; i++)); do

local funcname="${FUNCNAME[$i]}"

[ "$i" -eq "0" ] && funcname=$bash_command

echo -e " $i: ${BASH_SOURCE[$i+1]}:${BASH_LINENO[$i]}\t$funcname"

done

echo "Exiting with status ${code}"

exit "${code}"

}

# provide an error handler whenever a command exits nonzero

trap 'bash_traceback' ERR

# propagate ERR trap handler functions, expansions and subshells

set -o errtrace

The traceback will help you to know exactly which command in your Bash script exited with an error code different than “0”:

Error in ./test.sh:43 ('false' exited with status 1)
Traceback of ./test.sh (most recent call last):
  0: ./test.sh:43	false
  1: ./test.sh:49	main
Exiting with status -1

Error in ./test.sh:43 ('false' exited with status 1)

Traceback of ./test.sh (most recent call last):

0: ./test.sh:43 false

1: ./test.sh:49 main

Exiting with status -1

3. Check your Bash scripts with shellcheck and follow the recommendations of Advanced Bash-Scripting Guide.

Temporarily prevent Linux from shutting down

Posted on May 5, 2016 by Asher256

Accidental shutdown or reboot is a serious blunder, especially if the kernel is being updated in the background.

In order to prevent Linux from shutting down while your update script is running, I recommend you to use systemd-inhibit:

systemd-inhibit --why="Doing update" ./my-update-script.sh

1	systemd-inhibit --why="Doing update" ./my-update-script.sh

systemd-inhibit will block the shutdown or reboot until the update script is finished.

Additional options:

–who=”your name”
A human-readable name
—list
List all active inhibition locks

How to stop and remove all docker images and containers

Posted on May 3, 2016 by Asher256

Docker is a great tool, but sometimes it can consume a lot of disk space. docker-clean is a simple bash script you can use to remove all docker images and containers with one command:

$ git clone https://github.com/zzrotdesign/docker-clean
$ cd docker-clean
$ ./docker-clean --help
Options:
-h or --help        Opens this help menu
-v or --version     Prints the current docker-clean version

-a or --all         Stops and removes all Containers, Images, and Restarts docker
-c or --containers  Stops and removes Stopped and Running Containers
-i or --images      Stops and removes all Containers and Images
-net or --networks  Removes all empty Networks
-s or --stop        Stops all running Containers

--dry-run           Adding this additional flag at the end will list items to be
                    removed without running the remove or stop commands

-l or --log         Adding this as an additional flag will list all
                    image, volume, and container deleting output

$ git clone https://github.com/zzrotdesign/docker-clean

$ cd docker-clean

$ ./docker-clean --help

Options:

-h or --help Opens this help menu

-v or --version Prints the current docker-clean version

-a or --all Stops and removes all Containers, Images, and Restarts docker

-c or --containers Stops and removes Stopped and Running Containers

-i or --images Stops and removes all Containers and Images

-net or --networks Removes all empty Networks

-s or --stop Stops all running Containers

--dry-run Adding this additional flag at the end will list items to be

removed without running the remove or stop commands

-l or --log Adding this as an additional flag will list all

image, volume, and container deleting output

To stop and remove all Docker containers:

$ ./docker-clean --containers

1	$ ./docker-clean --containers

To remove all Docker images:

$ ./docker-clean --images

1	$ ./docker-clean --images

Welcome!

Posted on April 26, 2016 by Asher256

#!/usr/bin/env bash
echo "Welcome to Asher256's Blog!"
echo "A blog dedicated to Linux and Free Software."

#!/usr/bin/env bash

echo "Welcome to Asher256's Blog!"

echo "A blog dedicated to Linux and Free Software."

Asher256's Blog

DevOps/LINUX Engineer in Montreal, Canada

Author Archives: Asher256

About Asher256

Puppet module to configure LizardFS (Distributed File System) on Linux

3 advices to write robust Bash scripts

1. Activate the Bash options: errexit, nounset

2. Show a Bash Traceback

Temporarily prevent Linux from shutting down

How to stop and remove all docker images and containers

Welcome!