Creating a loop device (for testing)

==============================================
// create the backing file
# dd if=/dev/zero of=loopbackfile.img bs=100M count=10
10+0 records in
10+0 records out
1048576000 bytes (1.0 GB) copied, 1.26748 s, 827 MB/s

# du -sh loopbackfile.img
1000M loopbackfile.img

// get free loop device and associate with backing file
// -f free   ||  -P partscan to force kernel scan partition table
# losetup --show -fP loopbackfile.img

// show the devices
# losetup -a

// here loopX is the device associated - check with above step
# mkfs.xfs /dev/loopX


# mkdir -p /testdata

// do mount
# mount -o loop /dev/loop0 /testdata


// verify
# df -hP /loopfs/

# mount | grep testdata

==============================================

Gluster Storage in Kubernetes

I have made a presentation about Gluster Storage in Kubernetes. 

This is held in the joint meetup by  Kubernetes and Docker meetup groups.

https://events.docker.com/events/details/docker-bangalore-presents-joint-meetup-with-kubernetes-bangalore-managing-storage-with-containers

https://www.meetup.com/kubernetes-openshift-India-Meetup/events/253635989

https://www.meetup.com/Docker-Bangalore/events/253542738/

Thanks to the Organizers and J.P. Morgan Chase & Co. for hosting the event.

Presentation:

Ansible limiting to hosts/groups

Ansible limiting the playbook execution to few hosts / groups.


Limit to one host

ansible-playbook playbooks/PLAYBOOK_NAME.yml --limit "host1"








Limit to multiple hosts

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







All but one host




ansible-playbook playbooks/PLAYBOOK_NAME.yml --limit 'all:!host1'




Limit to a group




ansible-playbook playbooks/PLAYBOOK_NAME.yml --limit 'group1'




All but one group




ansible-playbook playbooks/PLAYBOOK_NAME.yml --limit 'all:!group1'

source:
https://ansible-tips-and-tricks.readthedocs.io/en/latest/ansible/commands/#limit-to-one-or-more-hosts

Better Battery management in Laptop

For better battery management in Laptops, use TLP.

yum install tlp -y


To start:
systemctl start tlp

To check status:
systemctl status tlp


Configuration here:
/etc/default/tlp


Ref: https://linrunner.de/en/tlp/docs/tlp-linux-advanced-power-management.html

git diff - some additional options

git diff with word level precision :)


// note there is a dot at the end
# git diff  --word-diff-regex=.


// git diff , avoiding lines around actual diff and showing only the diff.
# git diff -U0


more will be updated..

untar xz extension tar file

.tar.gz or .tgz extension -> z flag

-> tar zxvf <tar file. tgz>

-> gzip used here




.xz extension -> J flag

-> tar Jxvf <tar file . xz>

-> xz utils used here

Update a running docker container and create a new image

Sometimes during development, you may want to update few files inside docker container - and wish to create a new image out of it.

You can make use of docker commit.

first get the docker id of the images you wish to save. using docker ps

# docker ps

02738dcd4cc2


Then, make changes inside the docker container (02738dcd4cc2) .

For example,

docker exec -it 02738dcd4cc2 bash
# touch /root/testfile 
# edit some configuration


Now, exit the docker container (02738dcd4cc2) and save a new image.
# docker commit 02738dcd4cc2 <updated_docker_container_name_you_have_given>


Now, you can run this  <updated_docker_container_name_you_have_given>, to see the changes.


Use this option judiciously.

Ideally, you should always make use of Dockerfile to make changes and test :)

How to get package dependencies of a specific package

How to get package dependencies of a specific package ?


// so check the package exists
$ rpm -qa | grep vim-X11
vim-X11-8.0.600-1.fc24.x86_64


// Now, get all dependencies
$ rpm -q --requires  vim-X11
/bin/sh
/bin/sh
/bin/sh
gtk3
hicolor-icon-theme
libICE.so.6()(64bit)
libSM.so.6()(64bit)
libX11.so.6()(64bit)
libXt.so.6()(64bit)
libacl.so.1()(64bit)
libacl.so.1(ACL_1.0)(64bit)
libattr >= 2.4
libc.so.6()(64bit)
libc.so.6(GLIBC_2.11)(64bit)
libc.so.6(GLIBC_2.14)(64bit)
libc.so.6(GLIBC_2.15)(64bit)
libc.so.6(GLIBC_2.2.5)(64bit)
libc.so.6(GLIBC_2.3)(64bit)
libc.so.6(GLIBC_2.3.4)(64bit)
libc.so.6(GLIBC_2.4)(64bit)
libcairo.so.2()(64bit)
libdl.so.2()(64bit)
libdl.so.2(GLIBC_2.2.5)(64bit)
libgdk-3.so.0()(64bit)
libgdk_pixbuf-2.0.so.0()(64bit)
libgio-2.0.so.0()(64bit)
libglib-2.0.so.0()(64bit)
libgobject-2.0.so.0()(64bit)
libgpm.so.2()(64bit)
libgtk-3.so.0()(64bit)
libm.so.6()(64bit)
libm.so.6(GLIBC_2.2.5)(64bit)
libpango-1.0.so.0()(64bit)
libpangocairo-1.0.so.0()(64bit)
libpthread.so.0()(64bit)
libpthread.so.0(GLIBC_2.2.5)(64bit)
libselinux.so.1()(64bit)
libtinfo.so.6()(64bit)
perl(:MODULE_COMPAT_5.22.3)
rpmlib(CompressedFileNames) <= 3.0.4-1
rpmlib(FileDigests) <= 4.6.0-1
rpmlib(PayloadFilesHavePrefix) <= 4.0-1
rpmlib(PayloadIsXz) <= 5.2-1
rtld(GNU_HASH)
vim-common = 2:8.0.600-1.fc24