CentOS 7 – No Reboot Required

In below example, I have RHEL 8 server with 100 GB OS disk, the partitions are distributed between:

root = 50 GB
home = 46.3 GB
swap = 2.1 GB

Filesystem: xfs, however it should work with ext partitions.

The requirement to fulfill here is to extend the root partition from 50 GB to 100 GB.

Ok, Let’s find the device where root “/” partition is:

# lsblk

NAME            MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda               8:0    0  100G  0 disk
├─sda1            8:1    0  600M  0 part /boot/efi
├─sda2            8:2    0    1G  0 part /boot
└─sda3            8:3    0 98.4G  0 part
├─rhel-root   253:0    0   50G  0 lvm  /
├─rhel-swap   253:1    0  2.1G  0 lvm  [SWAP]
└─rhel-home   253:2    0 46.3G  0 lvm  /home

#==> /dev/sda is my OS disk, root partition is on /dev/sda3

Find device with LVM PV Scan

#pvs

PV         VG    Fmt  Attr PSize    PFree
/dev/sda3  rhel  lvm2 a--    98.41g    0
/dev/sdb1  vgapp lvm2 a--  <200.00g    0

My server is running on VMware vSphere environment, I have increased the disk size on VM from 100 GB to 150 GB and we will be increasing the space without rebooting/restarting the server.

VM Edit Settings > Disk Size Increase from 100 to 150 GB

Note: My server was already deployed with LVM configuration in place initially, we are just leveraging the LVM to extend the partition in this case.

Let us Rescan Extended Disk in OS to make Linux Kernel Aware, non-reboot method

# echo 1 > /sys/class/block/sda/device/rescan

Validate New Disk Size on sda

#lsblk

NAME            MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda               8:0    0  150G  0 disk
├─sda1            8:1    0  600M  0 part /boot/efi
├─sda2            8:2    0    1G  0 part /boot
└─sda3            8:3    0 98.4G  0 part
├─rhel-root   253:0    0   50G  0 lvm  /
├─rhel-swap   253:1    0  2.1G  0 lvm  [SWAP]
└─rhel-home   253:2    0 46.3G  0 lvm  /home

#==> sda size changed from 100 GB to 150 GB

Note: The partition is not automatically adjusted and needs to be resized in two steps

resizing the partition
make the kernel aware of the bigger partition

Now typically we use fdisk for the first step and a utility like partprobe (or a reboot) for the second step. But we now have a great software called growpart which we will use here. growpart is part of the cloud-utils-package, and should be available in your distro’s repositories. In my case it was not installed so let’s install it.

#yum install -y cloud-utils-growpart

Let’s increase the partition now with growpart.

As identified by #lsblk, our:

Device = /dev/sda ==> Disk of Root Partition

Partition = /dev/sda3 ==> Where our Root partition is.

#growpart /dev/sda 3
CHANGED: partition=3 start=3328000 old: size=206385152 end=209713152 new: size=311244767,end=314572767

#Note: there is a space in /dev/sda & 3 (3 was our partition number)

Let’s validate new partition size

#lsblk

NAME            MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda               8:0    0   150G  0 disk
├─sda1            8:1    0   600M  0 part /boot/efi
├─sda2            8:2    0     1G  0 part /boot
└─sda3            8:3    0 148.4G  0 part
├─rhel-root   253:0    0    50G  0 lvm  /
├─rhel-swap   253:1    0   2.1G  0 lvm  [SWAP]
└─rhel-home   253:2    0  46.3G  0 lvm  /home

#==> sda3 size changed from 98.4 GB to 148.5 GB

Let’s resize Physical Volume to occupy all new space

#pvresize /dev/sda3
1 physical volume(s) resized or updated / 0 physical volume(s) not resized

Validate with LVM PV Scan

#pvs

PV         VG    Fmt  Attr PSize    PFree
/dev/sda3  rhel  lvm2 a--   148.41g 50.00g
/dev/sdb1  vgapp lvm2 a--  <200.00g     0

#==> PSize changed for /dev/sda3

Let’s check the LVM volume group status

#vgs

VG    #PV #LV #SN Attr   VSize    VFree
rhel    1   3   0 wz--n-  148.41g 50.00g
vgapp   1   1   0 wz--n- <200.00g     0

#==> We have free space of 50 GB for rhel VG i.e our root partition VG

Let’s resize Logical Volume to occupy all new space

#lvextend -r -l +100%FREE /dev/rhel/root

Size of logical volume rhel/root changed from 50.00 GiB (12800 extents) to 100.00 GiB (25600 extents).
Logical volume rhel/root successfully resized.
meta-data=/dev/mapper/rhel-root  isize=512    agcount=4, agsize=3276800 blks
=                       sectsz=512   attr=2, projid32bit=1
=                       crc=1        finobt=1, sparse=1, rmapbt=0
=                       reflink=1
data     =                       bsize=4096   blocks=13107200, imaxpct=25
=                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0, ftype=1
log      =internal log           bsize=4096   blocks=6400, version=2
=                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
data blocks changed from 13107200 to 26214400

#==> example: #lvextend -r -l +100%FREE /dev/<name-of-volume-group>/root

Validate root partition should be increased to 100 GB now:

# lsblk

NAME            MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda               8:0    0   150G  0 disk
├─sda1            8:1    0   600M  0 part /boot/efi
├─sda2            8:2    0     1G  0 part /boot
└─sda3            8:3    0 148.4G  0 part
├─rhel-root   253:0    0   100G  0 lvm  /
├─rhel-swap   253:1    0   2.1G  0 lvm  [SWAP]
└─rhel-home   253:2    0  46.3G  0 lvm  /home

#==> rhel-root increased size.

Hope you find this article useful, share the love with others if you feel worth it.

Have a nice day.

Reset root password – RHEL7/8 CentOS 7/8

https://images.unsplash.com/photo-1584433144859-1fc3ab64a957?ixlib=rb-1.2.1&q=85&fm=jpg&crop=entropy&cs=srgb

Reboot your Server, at the bootloader screen select the kernel you would like to boot it with (usually the latest one) and hit ‘e’

In the next screen, find the line that refers to the kernel

For RHEL/CentOS 7, the line starts with ‘linux16’.
For RHEL/Centos 8x, and Fedora the line starts with ‘linux’.

Add ‘rd.break‘ at the end of kernel line and press Ctrl-x

Now the server will boot into OS rescue mode

switch_root:/#.

Now, remount root partition in read/write mode

#mount -o remount rw /sysroot

Next, switch to root directory

#chroot /sysroot

At this point you can change the root password

#passwd <enter>
*<new password>*
*<repeat new password>*

Next step is for SELinux to allow new file changes – such as password reset in our case.

#touch /.autorelabel

This step will take some time to relabel, as it depends on filesystem size

Once complete, Exit Server

#exit

then, Restart server

#reboot

Validate new password has been set on Server after reboot by logging in with root account.

Scan for new SCSI drives without the need to reboot the VM – LINUX

New disk presented to the running LINUX virtual machine will not display the device into operating system unless you reboot the server.

Found another way to achieve this and thought to note it down here for my future reference.

Run the following commands:

The first command returns the SCSI host in use which in this case is host2.:

grep mpt /sys/class/scsi_host/host?/proc_name

The next command, performs a bus scan.

echo “- – -“ > /sys/class/scsi_host/host2/scan

Fdisk is used to list all the available drives on the machine.

Validate if you can view new disk:

fdisk -l

If the newly added drive is still not discovered, then unfortunately just reboot the VM.

Content Referenced article: https://www.altaro.com/vmware/managing-disk-space-linux-vm/

Install MHA on RHEL6 / CentOS6 for mySQL

Configure Proxy for Internet

#export http_proxy=http://proxy.xxxx.intra:00
#export https_proxy=https://proxy.xxxx.intra:00

Note: My environment is using a proxy server for Internet access, if you have direct access to internet ignore this step.

Configure RedHat subscription for yum

#subscription-manager register –username admin-example –password secret –auto-attach

Download epel-release package on machine

#wget https://dl.fedoraproject.org/pub/epel/epel-release-latest-6.noarch.rpm

Note: the package will be downloaded on the path you are standing – verify from “pwd” command

Install epel-package

#yum install -y epel-release-latest-6.noarch.rpm

Install perl packages

#yum -y install perl-DBD-MySQL perl-Config-Tiny perl-Log-Dispatch perl-Parallel-ForkManager perl-Config-IniFiles ncftp perl-Params-Validate perl-CPAN perl-Test-Mock-LWP.noarch perl-LWP-Authen-Negotiate.noarch perl-devel

Install more perl packages

#yum install perl-ExtUtils-CBuilder perl-ExtUtils-MakeMaker

Download MHA Packages (Node & Manager)

https://code.google.com/p/mysql-master-ha/wiki/Downloads?tm=2

– MHA Manager 0.56 rpm RHEL6 – mha4mysql-manager-0.56-0.el6.noarch.rpm
– MHA Node 0.56 rpm RHEL6 – mha4mysql-node-0.56-0.el6.noarch.rpm

Once downloaded copy to server via WinSCP or SSH (somehow it is not working properly in wget for me)

Install MHA Packages

#yum -y install mha4mysql-node-0.56-0.el6.noarch.rpm

#yum -y install mha4mysql-manager-0.56-0.el6.noarch.rpm

Note: Move to directory where packages are downloaded

Docker – Basic Cheat Sheet

docker.com

As a learning curve, I had marked Docker in my list

So just tipping some quick commands for your and my own reference as it is not a primary tool I am using day-to-day

Display Docker Images:

$ docker images

Run Docker Image:

$ docker run hello-world

Note: If you do not have an image in your local machine, docker will look into docker hub (over the internet)

Write a docker file:

$ mkdir dockerfolder

$ cd dockerfolder

$ vim newdockerfile

RUN apt-get -y update && apt-get install -y telnet

save and close your newdockerfile “wq!”

Build and image from our Docker File

$ docker build -t telnet-install .

Note: we are using a period in the end of docker build command to represent the newdockerfile within the directory

If you want to run new build file: “docker run telnet-install”

Tag your image-id: (required if you want to push to docker hub)

$ docker tag 693bce725149 terminaltolinux/telnet-install:latest

Note: image id can be found from “docker images” command

$ docker login –username=terminaltolinux –email=terminal@linux.com

Note: after docker login command it will prompt for password, prior have a docker hub account

Push docker image to docker hub account:

$ docker push terminaltolinux/telnet-install

Note: Verify from docker hub account, the docker image will be pushed. Prior create a repo on docker hub

Delete a docker image:

$ docker rmi -f terminaltolinux/telnet-install

Pull docker image from docker hub account:

$ docker run terminaltolinux/telnet-install

Note: it will not find in the local machine as we deleted earlier and will fetch it online and run it, however “docker pull terminaltolinux/telnet-install” can also be used to just pull the image.

Search docker image:

$ docker search mysql

Search docker image with number of stars:

$ docker search -s 1 mysql

Run docker image in background:

$ docker run -d mysql

Run docker image with interactive session:

$ docker run -it ubuntu

List running containers

$ dockers ps

Inspect a container

$ docker inspect <container-id>

Note: container-id will be available from “docker ps”

Logs of standard error or standard out

$ docker log <container-id>

Commit changes to container and save as a separate image. (tag it):

$ docker commit <container-id> nginx-ubuntu

Port binding to container

$ docker run -d -p 6379 reds

Note: -p binds port but if we wanted to map this port directly on the host, we will use the option -p 6379:6379 and if with particular ip then -p 127.0.0.1:6379:6379

Binding directories

$ docker run -d -v “/home/docker/data”:/data reds

Start a container

$ docker start <container-id>

Stop a container

$ docker stop <container-id>

Remove an exited container

$ docker rm <container-id>

Restart a container

$ docker restart <container-id>

Use docker with proxy:

If you want to run docker with environment proxy, edit /etc/default/docker amend your entry for http_proxy

TIP:

If we don’t tell docker explicitly we want to map port, it will block access through that port (because containers are isolated until you tell them you want access)

ANSIBLE 2.0.2.0 – Basic Cheat Sheet – CentOS 6

Ansible.com

To install Ansible:

# wget http://download.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpminstall epel-release

# yum install epel-release-6-8.noarch.rpm

# yum update

# yum install ansible -y

Add remote hosts:

$ vim /etc/ansible/hosts

192.168.0.1 (your remote server IP) or
hostname.hostname.local (your remote server hostname)

Ping remote hosts: (if using ssh keys for authentication –ask-pass is not required)

$ ansible all -m ping –ask-pass

Ping remote hosts with specific account: (if using ssh keys for authentication –ask-pass is not required)

$ ansible all -m ping –ask-pass -u root

Execute command on remote server shell:

$ ansible all -m shell -a “mkdir /home/ansible/testdirectory” –ask-pass -u root

Remove file from remote server:

$ ansible all -m file -a “dest=/tmp/test.sh state=absent” –ask-pass -u root

Install apache on remote server:

$ ansible all -m yum -a “name=httpd state=latest” -u root

Change file permissions:

$ ansible all -m file -a “dest=/home/ansible/testfile.txt mode=600 owner=ansible group=anisble”

Confirm if package installed but do not update

$ ansible all -m yum -a “name=telnet state=present”

Confirm package is latest version

$ ansible all -m yum -a “name=telnet state=latest”

Confirm package is not installed

$ ansible all -m yum -a “name=telnet state=absent”

Start service

$ ansible all -m service -a “name=httpd state=started”

Restart service

$ ansible all -m service -a “name=httpd state=restarted”

Stop serivce

$ ansible all -m service -a “name=httpd state=stopped”

Gathering Facts

$ ansible all -m setup

Distribute Linux flavors in Ansible host file:

$ vim /etc/ansible/hosts

[RHEL]
192.168.1.1
rhel.redhat.test
[SUSE]
192.168.1.2
suse.opensuse.test

Only send instructions on RHEL hosts:

$ ansible RHEL -m shell -a “mkdir /home/ansible/testfolder”

Ansible use YaML for Automation and known as Playbook in Ansible

create a playbook i.e an .yaml file eg: telnetPlaybook.yaml

—
– hosts: SUSE
remote_user: root
tasks:
– zypper: name=telnet state=latest
– hosts: RHEL
remote_user: root
tasks:
– yum: name=telnet state=latest

Run playbook with Ansible: (-f switch allow the execution to be performed on multiple hosts parallel)

$ ansible-playbook telnetPlaybook.yaml -f 10

Ansible Modules (-m): These are few but there is huge list.

command – execute commands and this is default module of Ansible.
copy – copy files
shell – use remote shell to execute
file – file operations
ping – ping remote hosts
yum – Redhat package manager
git – use GIT
user – user creation, manipulation
service – manage services

If you find it interesting, spread the word 🙂

Add static proxy as Env Variable in CentOS / RedHat

PROXY

My office environment like many others are providing us Internet via proxy, on Windows Machine/Servers as they are part of domain the policy is pushed and as you login with your domain account you will find it available.

However on Linux servers I always go ahead with doing the following:

export http_proxy=http://proxy.blah.blah:80

And whenever the servers were required to reboot the proxy used to wipe out.

This time I made sure to make it static and plan to push it via Ansible to all the Linux babies I love.

Logged in from root account:

vim /etc/environment
http_proxy=http://proxy.blah.blah:80

Save the file – Re-initialize the shell or logout and login back. You will not have to re-add it back again.

To verify the variable

echo $http_proxy

How to Change Font Colors in CentOS / RedHat

Red & Turquoise Terminal

One of my monitor display was bothering my eyes, therefore I decided to change the colors being displayed on the monitor I am using, especially for the directory as it was dark blue and I had to dig myself inside the screen to actually read in that color. (my eyes are not week but I love small fonts)

I was not sure how to do it but knew it can be changed as I studied them long time ago, did some research and found out there are multiple ways to perform it.

As my environment is an Ansible lab therefore it did not click me to just change it for a specific user therefore I changed in environment base:

This is what I did: (from root user)

vim /etc/DIR_COLORS
DIR 01;96

Just above DIR value, I found out FILE parameter but it was commented, so i edited it to

vim /etc/DIR_COLORS
FILE 01;91

Now my terminal is displaying 96 = turquoise as DIR and 91 = light red as FILE and I like it !!

For you reference color codes:

0 = default colour
1 = bold
4 = underlined
5 = flashing text
7 = reverse field
31 = red
32 = green
33 = orange
34 = blue
35 = purple
36 = cyan
37 = grey
40 = black background
41 = red background
42 = green background
43 = orange background
44 = blue background
45 = purple background
46 = cyan background
47 = grey background
90 = dark grey
91 = light red
92 = light green
93 = yellow
94 = light blue
95 = light purple
96 = turquoise
100 = dark grey background
101 = light red background
102 = light green background
103 = yellow background
104 = light blue background
105 = light purple background
106 = turquoise background

I did not try it but if you are interested in changing it for specific user you can try this:

cp /etc/DIR_COLORS to $HOME/.dir_colors

once copied, edit you local copy i.e .dir_colors and play with it.

Don’t forget you need to re-initialize the shell or logout and login back for changes to take affect.

Install iftop, htop and NetHogs on RHEL / CentOS 6.x x86_64 [Internet Required]

Recently I was given a task to create two CentOS 6.5 Jump Servers in the environment I am working currently.

There was a specific requirement for the following packages.

iftop – Network Bandwidth Monitoring
htop – Linux Process Monitoring
NetHogs – Monitor per process Network Bandwidth

We have an internal secure proxy server via which Internet was easily available for my servers. This is how I did:

Step 1 – Enable EPEL (Extra Packages for Enterprise Linux) and install rpm

cd /tmp

wget http://download.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm

rpm -ivh epel-release-6-8.noarch.rpm

Step 2 – Verify EPEL Repo

yum repolist

(it should display EPEL repo in the output)

Step 3 – Install packages

yum -y install iftop

yum -y install htop

yum – y install NetHogs

Note: Just in case you face the following error:

yum error “Cannot retrieve metalink for repository: epel. Please verify its path and try again”

You will have to edit the following repo’s by commenting entries ‘mirrorlist=..’ and un-comment entries ‘baseurl=…’

/etc/yum.repos.d/epel.repo
/etc/yum.repos.d/epel-testing.repo