linux

DISCLAIMER: this is not my post is only a copy, in case the original get deleted or whatever, posting on my personal blog get easier for me to find it. You can find the original one in this link https://vpsie.com/knowledge-base/boot-single-user-mode-centos-rhel-vpsie/

The first thing to do is to open Terminal and log in to you CentOS 7 server.

After, restart your server wait for GRUB boot menu to show.

Next step is to select your Kernel version and press

You're working on an XFS filesystem, in this case you need to use xfs_growfs instead of resize2fs. Two commands are needed to perform this task :

# growpart /dev/sda 1

growpart is used to expand the sda1 partition to the whole sda disk.

# xfs_growfs -d /dev/sda1

xfs_growfs is used to resize and apply the changes.

# df -h

Sometimes you need to change the password to an user in a qcow2 image, to test locally or if you are using an infrastructure without cloud-init, regardless the user the procedure is the same.

Depends on the system the packages name could change a little, I'm using Fedora 27 I have installed

In any kind of distributed system you will have to choose between consistency, availability and partitioning, the CAP theorem states that in the presence of a network partition, one has to choose between consistency and availability, by default (default configurations) CEPH provides consistency and partitioning, just take in count that CEPH has many config options: ~860 in hammer, ~1100 in jewel, check this out, is jewel github co

Monitors can be severely affected by significant clock skews across the monitor nodes. This usually translates into weird behavior with no obvious cause. To avoid such issues, you should run a clock synchronization tool on your monitor nodes by default the monitors will allow clocks to drift up to 0.05 seconds.

This error can be seen using:

# ceph -s
# ceph health detail

I don't recall any reason to do this other than using the same user and auth key to authenticate in different Ceph clusters, like in a multi-backend solution, or just because things get messy when you are not using a default configuration.

Sometimes, things gets easy when we use the same user and auth key on both clusters for services to connect to, so lets see some background commands for managing users, keys and permissions:

Create new user and auth token (cinder client example):

Suppose that you want to migrate an instance from differents infrastructures or you want to handover and instance information to a client, so you need to recover (export) the instance volumes information.

Step 1: Get the instance UUID.

I thing we pass the part of what juju is and how it works, so I'll post direct commands and configurations of how getting the environment working inside a LXC container, created just for juju, not the local configuration that creates and LXC container, in other words, out host server does not have any juju package.

Some links to read in case you need more info, or you can post a question.

Let's assume you want to change ownership of volume from Tenant_A to Tenant_B.

Step 1: Tenant A will initiate an Ownership Transfer which will enable another tenant to take ownership of it.

$ source openrc Tenant_A Tenant_A
$ cinder transfer-create [volume_id]

An Authentication Key and a Transfer ID are returned here.

Step 2: Tenant B needs to accept the Transfer using the Transfer ID and The Authentication Keygenerated above.

An architecture trying to respond a least 10000 concurrent connections per second, is trying to solve the C10K problem, even if this is so last decade is still breaking servers, architectures and configurations, giving to sysadmins real headaches and not always because of real connections, also for basic DDoS attacks (pretty much is the same concept: lots and lots of new connections to the same service).