The screen command

useful for:

collaboration:

1. share screens with colleages
2. long running jobs. e.g. cp 100GB to an NFS. You can monitor progress by going back the screen.

https://www.lynda.com/Linux-tutorials/Manage-terminal-sessions-screen/618702/729627-4.html


What are the advantages of using Hashicorp Consul?

Consul is actually a 4 services combined seamless into a single service. that have been combined into one. These individual services are:

Service Discovery: All boxes (mysql servers, apache servers, ntp server, api servers…etc) will have the consul agent deamon running on them which will notify the consul server of it’s existence and the type of service it offers. The consul server will register that box under the given service name, of which multiple other boxes can be members of. Then when dns lookup request comes in for a given service then the Consul service will provide the ip address of one of the boxes in the service cluster, in a round robin fashion.

Health Checking: The consul agent will also give information about what health checking should be done


RHCE Quiz

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This article is part of our RHCE Study guide (click on the yellow tab on the far left). By the end of this article you should be able to answer the following questions:


Samba – Set up private group folders RHEL/CentOS 7

A common scenario is to provide a samba share to a particular group of people, where each group member has full read+write access to all the content stored in the Samba share. You can follow along this article using our Samba group collaboration vagrant project on github.

There’s a few ways to set up group collaboration in Samba. To start with we first need to create a standard Samba Server and Samba Client. After that on the Samba Server side we need to do the following:

  1. Create new OS Linux group that will have access to the samba share – (server and clients)
  2. Create Linux users and add them to this group – (server and clients)
  3. Also register the newly create Linux users with the Samba – (server only)
  4. Create the new folder

Samba – How to set up a Samba client on CentOS/RHEL 7

If you have directories on your machine that you want to share out to other machines then you can do this by setting up your machine as an NFS server. However with NFS you can only share out folders to machine that are in the same private network. If you want share folders to other machines over the public internet, then that’s where you need to use the Samba/CIFS protocol. You can follow along this article using this vagrant project on Github.

We will walk through the following example:

+--------------------------+              +--------------------------+
|                        															

NFS – How to set up an NFS client on CentOS/RHEL 7

Network Files System (NFS) is a protocol that let’s one Linux box (NFS server) to share a folder with another Linux box (NFS Client). On the NFS client this shared folder looks like just an ordinary folder. NFS only works in an internal network so you can share folders over the public internet.

This article doesn’t cover how to setup an NFS server, instead we will assume that we already have an NFS server already setup and we want to configure an NFS client to connect to it. We created a NFS vagrant project on github to help you following along with this example. In our example we have:

+--------------------------+              +--------------------------+
|      															

RHCE – Setting up an Apache Web Server (httpd) on CentOS/RHEL 7

In this series of articles we’re going to set up an Apache Web Server and walkthrough the various Apache configurations and features. To start with this article will cover setting up a basic Apache server with the default out-of-the-box apache configurations.

You can follow along with this Apache Vagrant project. This vagrant project is made up of 2 CentOS7 boxes, one box will act as our webserver (webserver.local – 10.0.5.10) and the other will act as our client (box1.local – 10.0.5.11).

We will also ensure:

  1. firewalld is running and not blocking web server traffic
  2. SELinux is in targeted mode

But for this walkthrough we will initially keep them turned off:

[root@webserver ~]# systemctl stop firewalld
[root@webserver ~]# setenforce Permissive

Installing Apache Software

This is done using yum to install httpd:

[root@webserver ~]# yum install httpd

This

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What is the command to install Apache web server?

$ yum group install ‘Basic Web Server’

What is the commadn to install a few text based web browsers?

$ yum install elinks lynx

What is the command to start+enable the apache service?

$ systemctl start httpd
$ systemctl enable httpd

What is the command to open up the firewalls?

$ firewall-cmd –add-service=http
$ firewall-cmd –add-service=https
$ systemctl restart firewalld


RHCE – An Walkthrough of the main Apache Configuration file on CentOS/RHEL 7

Nearly all of Apache’s config files are stored under three high-level directories:

[root@webserver httpd]# tree /etc/httpd/conf /etc/httpd/conf.d /etc/httpd/conf.modules.d
<strong>/etc/httpd/conf</strong>
├── httpd.conf
└── magic
<strong>/etc/httpd/conf.d</strong>
├── autoindex.conf
├── fcgid.conf
├── manual.conf           # This came from installing the httpd-manual rpm
├── README
├── ssl.conf              # This came from installing the mod_ssl rpm
├── userdir.conf
└── welcome.conf
<strong>/etc/httpd/conf.modules.d</strong>
├── 00-base.conf
├── 00-dav.conf
├── 00-lua.conf
├── 00-mpm.conf
├── 00-proxy.conf
├── 00-ssl.conf
├── 00-systemd.conf
├── 01-cgi.conf
└── 10-fcgid.conf

Other rpms can drop files into the *.d directories.

There are quite a few config files that comes with apache, but the main ones are /etc/httpd/conf/httpd.conf and /etc/httpd/conf.d/ssl.conf. Here’s what httpd.conf looks like:

[root@webserver conf]# cat /etc/httpd/conf/httpd.conf
#
# This is the main Apache HTTP server configuration file.  It contains the
# configuration directives that give the server its instructions.
# See <URL:http://httpd.apache.org/docs/2.4/> for detailed information.
# In particular, see
# <URL:http://httpd.apache.org/docs/2.4/mod/directives.html>
# for a discussion of each configuration directive.
#
# Do NOT simply read the instructions in here without understanding
# what they do.  They're here only as hints or reminders.  If you are unsure
# consult the online docs. You have been warned.
#
# Configuration and logfile names: If the filenames you specify for many
# of the server's control files begin with "/" (or "drive:/" for Win32), the
# server will use that explicit path.  If the filenames do *not* begin
# with "/", the value of ServerRoot is prepended -- so 'log/access_log'
# with ServerRoot set to '/www' will be interpreted by the
# server as '/www/log/access_log', where as '/log/access_log' will be
# interpreted as '/log/access_log'.
 
#
# ServerRoot: The top of the directory tree under which the server's
# configuration, error, and log files are kept.
#
# Do not add a slash at the end of the directory path.  If you point
# ServerRoot at a non-local disk, be sure to specify a local disk on the
# Mutex directive, if file-based mutexes are used.  If you wish to share the
# same ServerRoot for multiple httpd daemons, you will need to change at
# least PidFile.
#
ServerRoot "/etc/httpd"
 
#
# Listen: Allows you to bind Apache to specific IP addresses and/or
# ports, instead of the default. See also the <VirtualHost>
# directive.
#
# Change this to Listen on specific IP addresses as shown below to
# prevent Apache from glomming onto all bound IP addresses.
#
#Listen 12.34.56.78:80
Listen 80
 
#
# Dynamic Shared Object (DSO) Support
#
# To be able to use the functionality of a module which was built as a DSO you
# have to place corresponding `LoadModule' lines at this location so the
# directives contained in it are actually available _before_ they are used.
# Statically compiled modules (those listed by `httpd -l') do not need
# to be loaded here.
#
# Example:
# LoadModule foo_module modules/mod_foo.so
#
Include conf.modules.d/*.conf
 
#
# If you wish httpd to run as a different user or group, you must run
# httpd as root initially and it will switch.
#
# User/Group: The name (or #number) of the user/group to run httpd as.
# It is usually good practice to create a dedicated user and group for
# running httpd, as with most system services.
#
User apache
Group apache
 
# 'Main' server configuration
#
# The directives in this section set up the values used by the 'main'
# server, which responds to any requests that aren't handled by a
# <VirtualHost> definition.  These values also provide defaults for
# any <VirtualHost> containers you may define later in the file.
#
# All of these directives may appear inside <VirtualHost> containers,
# in which case these default settings will be overridden for the
# virtual host being defined.
#
 
#
# ServerAdmin: Your address, where problems with the server should be
# e-mailed.  This address appears on some server-generated pages, such
# as error documents.  e.g. admin@your-domain.com
#
ServerAdmin root@localhost
 
#
# ServerName gives the name and port that the server uses to identify itself.
# This can often be determined automatically, but we recommend you specify
# it explicitly to prevent problems during startup.
#
# If your host doesn't have a registered DNS name, enter its IP address here.
#
#ServerName www.example.com:80
 
#
# Deny access to the entirety of your server's filesystem. You must
# explicitly permit access to web content directories in other
# <Directory> blocks below.
#
<Directory />
    AllowOverride none
    Require all denied
</Directory>
 
#
# Note that from this point forward you must specifically allow
# particular features to be enabled - so if something's not working as
# you might expect, make sure that you have specifically enabled it
# below.
#
 
#
# DocumentRoot: The directory out of which you will serve your
# documents. By default, all requests are taken from this directory, but
# symbolic links and aliases may be used to point to other locations.
#
DocumentRoot "/var/www/html"
 
#
# Relax access to content within /var/www.
#
<Directory "/var/www">
    AllowOverride None
    # Allow open access:
    Require all granted
</Directory>
 
# Further relax access to the default document root:
<Directory "/var/www/html">
    #
    # Possible values for the Options directive are "None", "All",
    # or any combination of:
    #   Indexes Includes FollowSymLinks SymLinksifOwnerMatch ExecCGI MultiViews
    #
    # Note that "MultiViews" must be named *explicitly* --- "Options All"
    # doesn't give it to you.
    #
    # The Options directive is both complicated and important.  Please see
    # http://httpd.apache.org/docs/2.4/mod/core.html#options
    # for more information.
    #
    Options Indexes FollowSymLinks
 
    #
    # AllowOverride controls what directives may be placed in .htaccess files.
    # It can be "All", "None", or any combination of the keywords:
    #   Options FileInfo AuthConfig Limit
    #
    AllowOverride None
 
    #
    # Controls who can get stuff from this server.
    #
    Require all granted
</Directory>
 
#
# DirectoryIndex: sets the file that Apache will serve if a directory
# is requested.
#
<IfModule dir_module>
    DirectoryIndex index.html
</IfModule>
 
#
# The following lines prevent .htaccess and .htpasswd files from being
# viewed by Web clients.
#
<Files ".ht*">
    Require all denied
</Files>
 
#
# ErrorLog: The location of the error log file.
# If you do not specify an ErrorLog directive within a <VirtualHost>
# container, error messages relating to that virtual host will be
# logged here.  If you *do* define an error logfile for a <VirtualHost>
# container, that host's errors will be logged there and not here.
#
ErrorLog "logs/error_log"
 
#
# LogLevel: Control the number of messages logged to the error_log.
# Possible values include: debug, info, notice, warn, error, crit,
# alert, emerg.
#
LogLevel warn
 
<IfModule log_config_module>
    #
    # The following directives define some format nicknames for use with
    # a CustomLog directive (see below).
    #
    LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\"" combined
    LogFormat "%h %l %u %t \"%r\" %>s %b" common
 
    <IfModule logio_module>
      # You need to enable mod_logio.c to use %I and %O
      LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\" %I %O" combinedio
    </IfModule>
 
    #
    # The location and format of the access logfile (Common Logfile Format).
    # If you do not define any access logfiles within a <VirtualHost>
    # container, they will be logged here.  Contrariwise, if you *do*
    # define per-<VirtualHost> access logfiles, transactions will be
    # logged therein and *not* in this file.
    #
    #CustomLog "logs/access_log" common
 
    #
    # If you prefer a logfile with access, agent, and referer information
    # (Combined Logfile Format) you can use the following directive.
    #
    CustomLog "logs/access_log" combined
</IfModule>
 
<IfModule alias_module>
    #
    # Redirect: Allows you to tell clients about documents that used to
    # exist in your server's namespace, but do not anymore. The client
    # will make a new request for the document at its new location.
    # Example:
    # Redirect permanent /foo http://www.example.com/bar
 
    #
    # Alias: Maps web paths into filesystem paths and is used to
    # access content that does not live under the DocumentRoot.
    # Example:
    # Alias /webpath /full/filesystem/path
    #
    # If you include a trailing / on /webpath then the server will
    # require it to be present in the URL.  You will also likely
    # need to provide a <Directory> section to allow access to
    # the filesystem path.
 
    #
    # ScriptAlias: This controls which directories contain server scripts.
    # ScriptAliases are essentially the same as Aliases, except that
    # documents in the target directory are treated as applications and
    # run by the server when requested rather than as documents sent to the
    # client.  The same rules about trailing "/" apply to ScriptAlias
    # directives as to Alias.
    #
    ScriptAlias /cgi-bin/ "/var/www/cgi-bin/"
 
</IfModule>
 
#
# "/var/www/cgi-bin" should be changed to whatever your ScriptAliased
# CGI directory exists, if you have that configured.
#
<Directory "/var/www/cgi-bin">
    AllowOverride None
    Options None
    Require all granted
</Directory>
 
<IfModule mime_module>
    #
    # TypesConfig points to the file containing the list of mappings from
    # filename extension to MIME-type.
    #
    TypesConfig /etc/mime.types
 
    #
    # AddType allows you to add to or override the MIME configuration
    # file specified in TypesConfig for specific file types.
    #
    #AddType application/x-gzip .tgz
    #
    # AddEncoding allows you to have certain browsers uncompress
    # information on the fly. Note: Not all browsers support this.
    #
    #AddEncoding x-compress .Z
    #AddEncoding x-gzip .gz .tgz
    #
    # If the AddEncoding directives above are commented-out, then you
    # probably should define those extensions to indicate media types:
    #
    AddType application/x-compress .Z
    AddType application/x-gzip .gz .tgz
 
    #
    # AddHandler allows you to map certain file extensions to "handlers":
    # actions unrelated to filetype. These can be either built into the server
    # or added with the Action directive (see below)
    #
    # To use CGI scripts outside of ScriptAliased directories:
    # (You will also need to add "ExecCGI" to the "Options" directive.)
    #
    #AddHandler cgi-script .cgi
 
    # For type maps (negotiated resources):
    #AddHandler type-map var
 
    #
    # Filters allow you to process content before it is sent to the client.
    #
    # To parse .shtml files for server-side includes (SSI):
    # (You will also need to add "Includes" to the "Options" directive.)
    #
    AddType text/html .shtml
    AddOutputFilter INCLUDES .shtml
</IfModule>
 
#
# Specify a default charset for all content served; this enables
# interpretation of all content as UTF-8 by default.  To use the
# default browser choice (ISO-8859-1), or to allow the META tags
# in HTML content to override this choice, comment out this
# directive:
#
AddDefaultCharset UTF-8
 
<IfModule mime_magic_module>
    #
    # The mod_mime_magic module allows the server to use various hints from the
    # contents of the file itself to determine its type.  The MIMEMagicFile
    # directive tells the module where the hint definitions are located.
    #
    MIMEMagicFile conf/magic
</IfModule>
 
#
# Customizable error responses come in three flavors:
# 1) plain text 2) local redirects 3) external redirects
#
# Some examples:
#ErrorDocument 500 "The server made a boo boo."
#ErrorDocument 404 /missing.html
#ErrorDocument 404 "/cgi-bin/missing_handler.pl"
#ErrorDocument 402 http://www.example.com/subscription_info.html
#
 
#
# EnableMMAP and EnableSendfile: On systems that support it,
# memory-mapping or the sendfile syscall may be used to deliver
# files.  This usually improves server performance, but must
# be turned off when serving from networked-mounted
# filesystems or if support for these functions is otherwise
# broken on your system.
# Defaults if commented: EnableMMAP On, EnableSendfile Off
#
#EnableMMAP off
EnableSendfile on
 
# Supplemental configuration
#
# Load config files in the "/etc/httpd/conf.d" directory, if any.
IncludeOptional conf.d/*.conf

All these settings are defined in the Apache Directives Documentation.

Notice that in Apache, settings are referred to as Directives.

You should read this document in conjunction with the Directive Quick Reference Guide, and Dictionary dictionary.

You can also access them locally like this (if you have installed httpd-manual rpm):

$ elinks http://localhost/manual/mod/directives.html
$ elinks http://localhost/manual/mod/directive-dict.html
$ elinks http://localhost/manual/mod/quickreference.html

Let’s take a look at some of these setting in turn:

The ‘ServerRoot’ setting

The ServerRoot sets the location where all of Apache’s configurations and logs are stored. Some


RHCE – Controlling access using Apache’s Order, Deny, and Allow directives on CentOS/RHEL 7

Apache let’s you Allow/Deny access based on who is requesting access using the Order directive which is used in conjunction with the Allow and Deny directives.

You can sepcify multiple Allow and Deny rules like this:

Deny from {ip address}
Allow from {192.168.10.0/24}
Deny from dodgydomain.com


Order deny,allow

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question?

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RHCE – Setting up login based authentication using Apache on CentOS/RHEL 7

In the previous tutorial, we saw how we can host multiple websites on the same box using vhosts. Now we’ll look at how we can configure Apache to password protect some web content. In Apache you can set up authentication so that when a user attempts to access a given folder’s content, then they will get a prompt to enter a valid username and password. There’s 2 ways to do this:

  • Setup user-based security – This is where you only give one user account access to restricted part of your website
  • Setup group-managed content – this is where you give a group of people access to a restricted part of your website

Need to rewrite to article like this: first create 2 users tom and jerry. Then setup to only give tom access.