How To Install Docker on Centos 7 and Red Hat 7

Hello friends, I’m starting some posts referring to a Docker.
During the next months, we will make an update more frequent, all of us who have a suggestion please send an email to: geraldo@techpoli.info.

Introduction:

Docker is a software technology providing containers, promoted by the company Docker, Inc. Docker provides an additional layer of abstraction and automation of operating-system-level virtualization on Windows and Linux. Docker uses the resource isolation features of the Linux kernel such as cgroups and kernel namespaces, and a union-capable file system such as OverlayFS and others to allow independent “containers” to run within a single Linux instance, avoiding the overhead of starting and maintaining virtual machines.

The Linux kernel’s support for namespaces mostly isolates an application’s view of the operating environment, including process trees, network, user IDs and mounted file systems, while the kernel’s cgroups provide resource limiting, including the CPU, memory, block I/O, and network. Since version 0.9, Docker includes the libcontainer library as its own way to directly use virtualization facilities provided by the Linux kernel, in addition to using abstracted virtualization interfaces via libvirt, LXC (Linux Containers) and systemd-nspawn.

Step 1: Installation of Docker

As a matter of best practice we’ll update our packages:

yum -y update

Now run this command. It will add the official Docker repository, download the latest version of Docker and install it:

curl -fsSL https://get.docker.com/ | sh

Step 2: Start the docker and configure to start with the operating system.

Set the Docker service to start at boot:

systemctl enable docker

Then start the Docker service:

systemctl start docker

And verify your work by checking the status of Docker:

systemctl status docker

Step 3: Download Container

Download the centos Docker image:

Note you can choose any system like Ubuntu or Debian.

docker pull centos

Step 4: Run Container

As an example, let’s run a container using the latest image of CentOS. The combination of the -i and -t switches gives you interactive shell access into the container:

docker run -i -t centos /bin/bash

You are now using a docking dock inside a docker centos.

To disconnect or detach from the shell without exiting, use a string of Ctrl + Ctrl-p + Ctrl-q.

There are many community containers already available that can be found through a survey. On the command below, I look for a Ubuntu keyword:

docker search ubuntu:17.04

Friends, that’s all.
We will continue with more advanced articles on docker.

Continue Reading

Installing VMware Tools in a Linux virtual machine on Centos 7 and Red Hat 7

To install VMware Tools in a Linux guest operating system using Compiler:

1-Ensure that your Linux virtual machine is powered on.

2- If you are running a GUI interface, open a command shell.

Note: Log in as a root user, or use the sudo command to complete each of these steps.

3-Click VM in the virtual machine menu, then click Guest > Install/Upgrade VMware Tool

4-Click OK.

Note: In some cases, verify that the CDROM device is Connected from within the Edit Settings option of the virtual machine.

5-  To create a mount point, run:

mkdir /mnt/cdrom

6- To mount the CDROM, run:

mount /dev/cdrom /mnt/cdrom

7- To copy the Compiler gzip tar file to a temporary local directory, run:

cp /mnt/cdrom/VMwareTools-version.tar.gz /tmp/

Where version is the VMware Tools package version.

8-  To determine the version of VMware tools, run:

ls /mnt/cdrom

You see output similar to:

# VMwareTools-5.0.0-12124.tar.gz

9- To change to the tmp directory and extract the contents of the tar file into a new directory called vmware-tools-distrib, run:

cd /tmp
tar -zxvf VMwareTools-version.tar.gz

10- To change directory to vmware-tools-distrib and run the vmware-install.pl PERL script to install VMware Tools, run:

cd vmware-tools-distrib
./vmware-install.pl

Notes:
Complete the screen prompts to install the VMware Tools. Options in square brackets are default choices and can be selected by pressing Enter.
To compile VMware Tools successfully, you need gcc Compiler and Linux Kernel sources provided by your Linux distribution. Consult your Linux distribution documentation for details on methods to install these packages.
It is normal for the console screen to go blank for a short time during the installation when the display size changes.
Some warnings or errors are normal, like when a files does not exist.
Depending on the Linux distribution, your network service might restart after installation. VMware recommends that you invoke this command from the console and not remotely.

11- If you are running a GUI interface, restart your X Window session for any mouse or graphics changes to take effect.

12-  To start VMware Tools running in the background during an X Window session, run:

/usr/bin/vmware-toolbox &

13- Depending on your environment, you may need to unmount the CD-ROM. To unmount the CD-ROM, run:

umount /mnt/cdrom

14- Depending on your environment, you may need to manually end the VMware Tools installation. To end the VMware Tools install, click VM in the virtual machine menu, then click Guest > End VMware Tools Install.

15-To remove VMware Tools installation packages, run:

cd
rm /tmp/VMwareTools-version.tar.gz
rm -rf /tmp/vmware-tools-distrib

That is all

Continue Reading

How to Block Ping ICMP Responses in Linux System

Blocking ping responses from system can prevent system from hackers to ICMP flood dos attacks. So it can be a best practice for system security but most of online monitoring systems uses ping requests for monitoring system.

Disable Ping using iptables

You can simply block icmp responses directly from firewall in any Linux systems.

# iptables -A INPUT -p icmp --icmp-type echo-request -j DROP

Block Ping with Kernel Parameter

We can also block ping responses from system by directly updating kernel parameters. In this we can block ping responses temporarily or permanently as below.

Block Ping Temporarily

You can block temporarily block ping responses temporarily using following command

# echo "1" > /proc/sys/net/ipv4/icmp_echo_ignore_all

Block Ping Permanently
In place of blocking ping temporarily, You can block it permanently by adding following parameter in /etc/sysctl.conf configuration file.

net.ipv4.icmp_echo_ignore_all = 1

Now execute following command to apply settings immediately without rebooting system.

# sysctl -p
Continue Reading

Linux and Unix nohup command

About nohup

When using the command shell, prefixing a command with nohup prevents the command from being aborted if you log out or exit the shell.
The name nohup stands for “no hangup.” The hangup (HUP) signal, which is normally sent to a process to inform it that the user has logged off (or “hung up”), is intercepted by nohup, allowing the process to continue running.

 

Nohup syntax

nohup COMMAND [ARG]...
nohup OPTION...

Options

--help display a help message and exit.
--version output version information and exit.

If standard input is a terminal, nohup redirects it from /dev/null. If standard output is a terminal, append output to “nohup.out” if possible, “$HOME/nohup.out” otherwise. If standard error is a terminal, redirect it to standard output. To save output to file FILE, use “nohup COMMAND > FILE”.

Nohup examples

nohup find -size +100k > log.txt &
Run the find command, instructing it to search for any file bigger then 100 kilobytes. find will continue to search even if the user logs out, and write its results to the file log.txt.
The “&” symbol at the end of the command runs find in the background, returning you to the command prompt while it is running. It is normal to use nohup in conjunction with & if you want to continue running other commands.

Related commands

nice — Invoke a command with an altered scheduling priority.

Continue Reading

Oracle Database 12c Release Installation On Oracle Linux 7

Download Software

Download the Oracle software from OTN or MOS depending on your support status.

OTN: Oracle Database 12c Release 1 (12.1.0.2) Software (64-bit).
edelivery: Oracle Database 12c Release 1 (12.1.0.2) Software (64-bit)

This article has been updated for the 12.1.0.2 release, but the installation is essentially unchanged since 12.1.0.1. Any variations specific for 12.1.0.1 will be noted.

Depending on your version of VirtualBox and Oracle Linux, there may be some slight variation in how the screen shots look.
Unpack Files

Unzip the files.

unzip linuxamd64_12102_database_1of2.zip
unzip linuxamd64_12102_database_2of2.zip

You should now have a single directory called “database” containing installation files.

Hosts File

The “/etc/hosts” file must contain a fully qualified name for the server.

<IP-address> <fully-qualified-machine-name> <machine-name>

For example.

127.0.0.1       localhost.localdomain  localhost
192.168.0.210   ol7-121.localdomain    ol7-121

Oracle Installation Prerequisites

Perform either the Automatic Setup or the Manual Setup to complete the basic prerequisites. The Additional Setup is required for all installations.

Automatic Setup

If you plan to use the “oracle-rdbms-server-12cR1-preinstall” package to perform all your prerequisite setup, issue the following command.

# yum install oracle-rdbms-server-12cR1-preinstall -y

It is probably worth doing a full update as well, but this is not strictly speaking necessary.

# yum update

Manual Setup

If you have not used the “oracle-rdbms-server-12cR1-preinstall” package to perform all prerequisites, you will need to manually perform the following setup tasks.

Add or amend the following lines in the “/etc/sysctl.conf” file.

fs.file-max = 6815744
kernel.sem = 250 32000 100 128
kernel.shmmni = 4096
kernel.shmall = 1073741824
kernel.shmmax = 4398046511104
net.core.rmem_default = 262144
net.core.rmem_max = 4194304
net.core.wmem_default = 262144
net.core.wmem_max = 1048576
fs.aio-max-nr = 1048576
net.ipv4.ip_local_port_range = 9000 65500

Run the following command to change the current kernel parameters.

/sbin/sysctl -p

Add the following lines to the “/etc/security/limits.conf” file.

oracle soft nofile 1024
oracle hard nofile 65536
oracle soft nproc 16384
oracle hard nproc 16384
oracle soft stack 10240
oracle hard stack 32768

Install the following packages if they are not already present.

# From Public Yum or ULN
yum install binutils -y
yum install compat-libcap1 -y
yum install compat-libstdc++-33 -y
yum install compat-libstdc++-33.i686 -y
yum install gcc -y
yum install gcc-c++ -y
yum install glibc -y
yum install glibc.i686 -y
yum install glibc-devel -y
yum install glibc-devel.i686 -y
yum install ksh -y
yum install libgcc -y
yum install libgcc.i686 -y
yum install libstdc++ -y
yum install libstdc++.i686 -y
yum install libstdc++-devel -y
yum install libstdc++-devel.i686 -y
yum install libaio -y
yum install libaio.i686 -y
yum install libaio-devel -y
yum install libaio-devel.i686 -y
yum install libXext -y
yum install libXext.i686 -y
yum install libXtst -y
yum install libXtst.i686 -y
yum install libX11 -y
yum install libX11.i686 -y
yum install libXau -y
yum install libXau.i686 -y
yum install libxcb -y
yum install libxcb.i686 -y
yum install libXi -y
yum install libXi.i686 -y
yum install make -y
yum install sysstat -y
yum install unixODBC -y
yum install unixODBC-devel -y

Create the new groups and users.

groupadd -g 54321 oinstall
groupadd -g 54322 dba
groupadd -g 54323 oper
#groupadd -g 54324 backupdba
#groupadd -g 54325 dgdba
#groupadd -g 54326 kmdba
#groupadd -g 54327 asmdba
#groupadd -g 54328 asmoper
#groupadd -g 54329 asmadmin
#useradd -u 54321 -g oinstall -G dba,oper oracle

Uncomment the extra groups you require.

Additional Setup

The following steps must be performed, whether you did the manual or automatic setup.

Set the password for the “oracle” user.

passwd oracle

Amend the “/etc/security/limits.d/90-nproc.conf” file as described below. See MOS Note [ID 1487773.1]

# Change this
* soft nproc 1024

# To this
* - nproc 16384

Set secure Linux to permissive by editing the “/etc/selinux/config” file, making sure the SELINUX flag is set as follows.

SELINUX=permissive

Once the change is complete, restart the server or run the following command.

# setenforce Permissive

If you have the Linux firewall enabled, you will need to disable or configure it, as shown here or here. To disable it, do the following.

# service iptables stop
# chkconfig iptables off

Create the directories in which the Oracle software will be installed.

mkdir -p /u01/app/oracle/product/12.1.0.2/db_1
chown -R oracle:oinstall /u01
chmod -R 775 /u01

Putting mount points directly under root is typically a bad idea. It’s done here for simplicity, but for a real installation “/” should be reserved for the OS.
Unless you are working from the console, or using SSH tunnelling, login as root and issue the following command.

xhost +<machine-name>

Add the following lines at the end of the “/home/oracle/.bash_profile” file.

# Oracle Settings
export TMP=/tmp
export TMPDIR=$TMP

export ORACLE_HOSTNAME=ol6-121.localdomain
export ORACLE_UNQNAME=cdb1
export ORACLE_BASE=/u01/app/oracle
export ORACLE_HOME=$ORACLE_BASE/product/12.1.0.2/db_1
export ORACLE_SID=cdb1

export PATH=/usr/sbin:$PATH
export PATH=$ORACLE_HOME/bin:$PATH

export LD_LIBRARY_PATH=$ORACLE_HOME/lib:/lib:/usr/lib
export CLASSPATH=$ORACLE_HOME/jlib:$ORACLE_HOME/rdbms/jlib

Installation

Log into the oracle user. If you are using X emulation then set the DISPLAY environmental variable.

DISPLAY=<machine-name>:0.0; export DISPLAY

Start the Oracle Universal Installer (OUI) by issuing the following command in the database directory.

./runInstaller

Proceed with the installation of your choice.

Step 1

oracle_2

Step 2

oracle_1

Step 3

oracle_3

Step 4

oracle_4

Step 5

oracle_5

Step 6

oracle_6

Step 7

oracle_7

Step 8

oracle_8

Step 9

oracle_9

Step 10

oracle_10

Step 11

oracle_11

Step 12

oracle_12

Step 13

oracle_13

Step 14

oracle_14

Step 15

oracle_15

Step 16

oracle_16

Step 17

oracle_17

Step 18

oracle_18

Step 19

oracle_19

Step 20

oracle_20

Step 21

oracle_21

The installation was completed successfully.

Post Installation

Edit the “/etc/oratab” file setting the restart flag for each instance to ‘Y’.

cdb1:/u01/app/oracle/product/12.1.0.2/db_1:Y

If Database Express 12c is not working, check the XMLDB HTTP port. If it is 0, set it to the port you want to use.

SQL> SELECT dbms_xdb_config.gethttpsport FROM dual;
GETHTTPSPORT
------------
5500

SQL> EXEC dbms_xdb_config.sethttpsport(5500);

PL/SQL procedure successfully completed.

SQL>

Common Errors

  • “error code 35” : The machine name in the “/etc/hosts” file is not correct. It needs an entry for the loopback adapter (localhost) and the machine name. If you are using DNS for name resolution, you still need the loopback adapter reference in this file.
  • “error code 37” : The DNS not working properly. You may also get this error is the “/etc/hosts” file is not configured correctly.
  • “sqlplus: error while loading shared libraries: libclntsh.so.12.1” : The prerequisites have not been met. Work through them again. Specifically, make sure the “gcc” package has been installed.
  • Listener fails to start – Typically this is due to incorrect name resolution. Make sure the “/etc/hosts” and/or DNS is configured correctly.
  • Linking errors – Almost always due to missing prerequisites. Review the setup sections.

That is all. Any doubts I am available.

Continue Reading