How to Boot into Single User Mode in CentOS/RHEL 7

Submitted by alvaro.soto on Tue, 05/21/2019 - 12:39

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

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XFS online resize

Submitted by alvaro.soto on Wed, 04/17/2019 - 00:05

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

How to disable Cloud-Init in a EL Cloud Image

Submitted by alvaro.soto on Wed, 12/12/2018 - 13:20

So this one is pretty simple. However, I found a lot of misinformation along the way, so I figured that I would jot the proper (and most simple) process here.

Symptoms: a RHEL (or variant) VM that takes a very long time to boot. On the VM console, you can see the following output while the VM boot process is stalled and waiting for a timeout. Note that the message below has nothing to do with cloud init, but its the output that I have most often seen on the console while waiting for a VM to boot.

[106.325574} random: crng init done

Ceph recovery backfilling affecting production instances

Submitted by alvaro.soto on Wed, 06/14/2017 - 21:06

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

Solve Ceph Clock Skew error

Submitted by alvaro.soto on Wed, 11/16/2016 - 01:21

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

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Cloning a Ceph client auth key

Submitted by alvaro.soto on Wed, 11/16/2016 - 00:54

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):

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