Category Archives: Linux

GlusterFS

Example of GlusterFS configuration on 2 servers with Block Storage attached.

This setup is suggested for TESTING purposes only. In a production environment please verify performances.

Create a separate network and map IP/servers' names in /etc/hosts
Append to /etc/hosts
# GlusterFS
192.168.3.5     gfs01
192.168.3.6     gfs02

>> On BOTH nodes:

yum update
wget -P /etc/yum.repos.d http://download.gluster.org/pub/gluster/glusterfs/LATEST/CentOS/glusterfs-epel.repo
yum -y install parted lvm2 xfsprogs glusterfs glusterfs-fuse glusterfs-server
grep ^exclude /etc/yum.conf

[root@gfs01 sysconfig]# grep ^exclude /etc/yum.conf
exclude=gluster*
(in [main] section)

parted -s -- /dev/xvdb mktable gpt
parted -s -- /dev/xvdb mkpart primary 2048s 100%
parted -s -- /dev/xvdb set 1 lvm on
partx -a /dev/xvdb
pvcreate /dev/xvdb1 
vgcreate vggfs01 /dev/xvdb1 

lvcreate -l 100%VG -n gbrick1 vggfs01
mkfs.xfs -i size=512 /dev/vggfs01/gbrick1
echo '/dev/vggfs01/gbrick1 /data/gluster/gvol0 xfs inode64,nobarrier 0 0' >> /etc/fstab
mkdir -p /data/gluster/gvol0
mount /data/gluster/gvol0
mkdir -p /data/gluster/gvol0/brick1

/bin/systemctl start glusterd.service
/bin/systemctl status glusterd.service
systemctl enable glusterd.service

>> On NODE2
gluster peer probe gfs01
gluster peer status
gluster pool list

>> On NODE1
gluster peer probe gfs02
gluster peer status
gluster pool list

gluster volume create gvol0 replica 2 transport tcp gfs01:/data/gluster/gvol0/brick1 gfs02:/data/gluster/gvol0/brick1
gluster volume start gvol0
gluster volume info gvol0

gluster volume set gvol0 performance.cache-refresh-timeout 30
gluster volume set gvol0 performance.io-thread-count 32
gluster volume set gvol0 performance.cache-size 1073741824
gluster volume info gvol0



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

TO MOUNT - Fuse (HA)
=> nodes need to be connected to the same Cloud Network

Append to /etc/hosts
# GlusterFS
192.168.3.5     gfs01
192.168.3.6     gfs02

yum -y install glusterfs glusterfs-fuse

modprobe fuse

echo 'gfs01:/gvol0 /mnt/gluster/gvol0 glusterfs defaults,backupvolfile-server=gfs02,_netdev 0 0' >> /etc/fstab

mkdir -p /mnt/gluster/gvol0

mount /mnt/gluster/gvol0


==========================================================
It seems that Debian 7 cannot have GlusterFS 3.7 but only from Debian 8.
http://download.gluster.org/pub/gluster/glusterfs/3.7/3.7.0/Debian/jessie/


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

Extra source: http://matty.digital/gluster

Extra commands
# gluster volume remove-brick gvol0 gfs02:/data/gluster/gvol0/brick1 force
# gluster peer detach gfs02
# gluster peer detach gfs01
# gluster peer probe gfs01

GIT basic commands

Check branch

git branch <name new branch>

Show changes after your last commit

git diff

rollback to previous change (specific file) to the latest commit

git checkout -- testfile

Delete branch

git branch -D <branch name>

Push new branch to the origin (my ‘git space’)

git push -u origin <branch name>

Restore file from upstream

git checkout upstream/master -- <filename>

Commit changes in one single line

git commit -a -m "comment"

If you want to merge the recent changes committed on the master branch into your dev branch

git checkout dev      # gets you "on branch dev"
git fetch origin        # gets you up to date with origin
git merge origin/master

If you want to reset ALL from the version ‘on the web’

git fetch origin
git reset --hard origin/<branch>

Source: http://rogerdudler.github.io/git-guide/

Docker basic commands

Check containers

# docker ps -a

Connect to a container

# docker start <ID>
# docker attach <ID>

Exit from a container

-> type 'exit'

Remove all of Docker containers:

docker stop $(docker ps -a -q)
docker rm $(docker ps -a -q)

NSCD – Cache DNS requests

DNS queries can be an issue on Cloud infrastructure, where SaaS are generally configured using FQDN instead of IP. This means that every time your application needs MySQL or Redis or any of the Platform/Software as a service, a DNS query will be issued.

Sometimes this could hammer the local DNS and service providers might block your DNS traffic.

To minimise this, you could use nscd to cache the DNS queries and reduce the traffic to the local DNS servers.

>> Test if port 53 has been blocked
tcpdump -vvv -s 0 -l -n port 53

>> Check what is currently cached
nscd -g (and check hosts cache)

>> Configuration file
grep -v "^#" /etc/nscd.conf (leaving only 'hosts' details)

	server-user		nscd
	debug-level		0
	paranoia		no

	enable-cache		hosts		yes
	positive-time-to-live	hosts		3600
	negative-time-to-live	hosts		20
	suggested-size		hosts		211
	check-files		hosts		yes
	persistent		hosts		yes
	shared			hosts		yes
	max-db-size		hosts		33554432

Improve/Ubuntu-like Font Rendering in Debian using Infinality Font

/etc/apt/sources.list

#Infinality Fonts
deb http://ppa.launchpad.net/no1wantdthisname/ppa/ubuntu saucy main

apt-get install fontconfig-infinality

cd /etc/fonts/infinality/
bash infctl.sh setstyle

chose 3 (i.e. linux).

In /etc/profile.d/infinality-settings.sh --> search for “USE_STYLE” or scroll (around line 710) till you see the option to set the style => USE_STYLE=”UBUNTU”


Settings -> Appearance.

    Tick the checkbox to Enable anti-aliasing
    Set Sub-pixel order to RGB
    Set Hinting to Slight


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

Personally installed before also: cabextract fonts-liberation ttf-mscorefonts-installer


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

Other fonts:

1) Install pretty fonts (you'll need non-free for mscorefonts): apt-get install ttf-dejavu ttf-liberation ttf-mscorefonts-installer xfonts-terminus
2) dpkg-reconfigure fontconfig-config, select Autohinter, Automatic and No
3) dpkg-reconfigure fontconfig
4) Restart Xorg
5) Gnome-specific (these are largely personal preferences): System -> Preferences -> Appearances -> Fonts: Enable 'Best Shapes', Details -> Dots per Inch: 110, Smoothing -> Grayscale

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

Source: http://linuxpanda.wordpress.com/2014/03/14/improve-ubuntu-like-font-rendering-in-debian-using-infinality-font/

Rackspace – Reinstall Nova-Agent

apt-get purge nova-client
apt-get update && apt-get upgrade

Used this script to re-install nova-agent: https://github.com/rackerlabs/openstack-guest-agents-unix/blob/master/tools/nova-agent-builder.sh

>> extract the tar and ./install.sh

sed '1i### BEGIN INIT INFO\n# Provides: Nova-Agent\n# Required-Start: $remote_fs $syslog\n# Required-Stop: $remote_fs $syslog\n# Default-Start: 2 3 4 5\n# Default-Stop: 0 1 6\n# Short-Description: Start daemon at boot time\n# Description: Enable service provided by daemon.\n### END INIT INFO\n' /usr/share/nova-agent/1.39.1/etc/generic/nova-agent > /usr/share/nova-agent/1.39.1/etc/generic/nova-agent.lsb

cp /usr/share/nova-agent/1.39.1/etc/generic/nova-agent.lsb /etc/init.d/nova-agent

chmod +x /etc/init.d/nova-agent

service xe-linux-distribution stop
service xe-linux-distribution start
service nova-agent start

# ps aux | grep nova
root      7874  0.0  0.7 143984  7464 ?        Ssl  09:02   0:00 /usr/sbin/nova-agent -q -p /var/run/nova-agent.pid -o /var/log/nova-agent.log -l debug /usr/share/nova-agent/nova-agent.py
root      7890  0.0  0.0  11980   928 pts/0    S+   09:03   0:00 grep --color=auto nova


Sources:
http://www.syntheticworks.com/rackspace-cloud/linux-rackspace-cloud/all-about-nova-agent-linux/
https://github.com/rackerlabs/openstack-guest-agents-unix/blob/master/tools/nova-agent-builder.sh
http://bootrackspacecom.readthedocs.org/en/latest/nova_agent/

Rackspace Cloud – .localdomain added in /etc/hosts after reboot

There is an agent called “nova-agent” which runs on all Rackspace cloud virtualised servers. This agent handles all communication between the hypervisor and guest OS, and is used for decloning.

Because it is used during decloning, it owns the /etc/hosts file and many files related to DNS and networking (/etc/resolv.conf , /etc/sysconfig/network-scripts/ifcfg-eth0 ,etc)

It is unlikely, but possible, that the host reboot triggered nova-agent to reset your hosts file.

To prevent nova-agent from overwriting your files, you can change the attributes of the file using the following command:

# chattr +i /etc/hosts

This will make the file unwriteable even to root! To remove this restriction, use the following:

# chattr -i /etc/hosts

PHP Sessions in Redis

If your php application requires sessions and it’s hosted on a scaled high available infrastructure, it’s required to have these sessions stored on a decentralised and HA platform as well, in order to avoid to rely on session persistent options on the load balancer or another Cloud Server.
Redis as a Service is a nice fit for this purpose.

Here an example using Rackspace Object Rocket http://www.rackspace.co.uk/objectrocket/redis

To achieve this it’s required to install the right package.

In Centos/RHEL, there is the IUS package available:

yum install php56u-pecl-redis

After that, the php.ini should be changed like this:

 session.save_handler = redis 
 session.save_path = "tcp://REDISOBJECTROCKETFQDN:PORT?auth=REDISPASSWORD"

To increase performance and reduce the “noise” for repetitive DNS queries (especially in case of SaaS which uses FQDN instead of an IP) it is also recommended to install nscd to cache the DNS queries.

Rackspace Cloud – Get AUTH Token

USERNAME=<username>
APIKEY=<api_key>

curl -s -d \
'{
"auth":
{
"RAX-KSKEY:apiKeyCredentials":
{
"username": "$USERNAME",
"apiKey": "$APIKEY"}
}
}' \
-H 'Content-Type: application/json' \
'https://identity.api.rackspacecloud.com/v2.0/tokens' | python -m json.tool   | grep -i token -A5

My notepad

Chris' IT notes…