NFS Server and Client Configuration in RHEL / CENTOS / Fedora (Basic)

Server Side

NFS Package Installation

[root@system1 ~]# yum install nfs*

Create a shared directory with appropriate permission to access

[root@system1 ~]# cd /

[root@system1 /]# mkdir redhat

[root@system1 /]# ls

bin   dev  home  lost+found  misc  net  proc    root  selinux  sys  usr

boot  etc  lib   media       mnt   opt  redhat  sbin  srv      tmp  var

[root@system1 /]# cd redhat

Create sample files in to that

[root@system1 redhat]#  touch  ma ba ca

Check the service status

[root@system1 /]# service nfs status

rpc.mountd is stopped

nfsd is stopped

rpc.rquotad is stopped

Put a share entry in vim /etc/exports

[root@system1 /]# vim etc/exports

/redhat         192.168.0.100(rw)

~                                                                               

~                                                                               

~                                                                               

~                                                                               

~                                                                               

~                                                                               

"etc/exports" 1L, 27C

Start the service

[root@system1 /]# service nfs start

Starting NFS services:                                     [  OK  ]

Starting NFS quotas:                                       [  OK  ]

Starting NFS daemon:                                       [  OK  ]

Starting NFS mountd:                                       [  OK  ]

[root@system1 /]# chkconfig nfs on

Output verification

[root@system1 /]# exportfs

/redhat         192.168.0.100

Client Side

In client side create a directory to mount the NFS sharing what you made in server side.

[root@system2 /]# mkdir /data

Commands used at the client end to verify the sharing availability:-

[root@system2 /]# showmount -e <nfs server ip_address> ( or )

[root@system2 /]# showmount -e <nfs server hostname>   ( or )

[root@system2 /]# showmount -e <nfs server FQDN>

Mounting of NFS sharing

There are two types of mounting is possible, that is temporary mount and other is permanent mount by put an entry in /etc/fstab

[root@system2 /]# mount -t nfs 192.168.0.100:/redhat /data

Check this by type ls command and see the file content is present or not

Entry in vim /etc/fstab

[root@system2 /]# vim /etc/fstab

#

# /etc/fstab

# Created by anaconda on Mon Aug 13 21:49:03 2012

#

# Accessible filesystems, by reference, are maintained under '/dev/disk'

# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info

#

sysfs                     /sys     sysfs  defaults  0 0

proc                      /proc    proc   defaults  0 0

192.168.0.100:/redhat     /data    nfs    defaults  0 0

[root@system2 /]# mount -a

Now we have a permanent mount path for NFS file sharing in client machine.

That’s it….

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Rescue Linux Installation in RHEL / CENTOS / Fedora

Rescuing a Linux system is an easier task. There are several aspects of rescuing a Linux system.

Here we are going to see how to rescue an installed Linux system when the GRUB is deleted.

Suppose you are having a Linux system. Recently you installed a Windows OS into a new partition unchanging the Linux partitions. Once after you have installed Windows, the Linux no longer boots. This is because the windows install will overwrite the MBR thereby deleting / removing the GRUB boot loader.

In this case you are having the Linux partitions. Only thing is that it is not booting. Fixing this problem is very simple. Just install GRUB. That’s all to do.

Step 1: Boot from the install CD / DVD (net-install also)
Step 2: Select the “Rescue Installed System” in GUI

Or type in “linux rescue” command in the “boot: “

Now the system is booting the rescue image. Choose your language.

Select Keyboard type

The networking setup. We dont want the networking interfaces during the rescue process. So prefer opt the “No” option to not start the networking interfaces.

This step will now attempt to find your Linux installation and mount it under the directory /mnt/sysimage. So to continue select “Continue“.

Searching…
10-> 20-> 30-> 40-> 50-> 60-> 70-> 80-> 90-> 100

If the rescue environment was unable to find your Linux installation you will be getting a message like this.

And if the rescue environment was able to find the Linux installation, it will get mounted under the /mnt/sysimage directory.

Now Supply the following commands

sh-3.2# chroot /mnt/sysimage

sh-3.2# grub-install /dev/sda

Installation finished. No error reported.

This is the contents of the device map /boot/grub/device.map.

Check if this is correct or not. If any of the lines is incorrect,

fix it and re-run the script 'grub-install'.

# this device map was generated by anaconda

(hd0)     /dev/sda

/dev/sda is the name of you hdd. check it carefully.

Now reboot.

sh-3.2# reboot

Or

init 6 to reboot.

Now see your Linux OS in the OS chooser menu.

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Authentication / Password Protection in Apache

There are many ways you can password protect directories under Apache web server. This is important to keep your file privates from both unauthorized users and search engines (when you do not want to get your data indexed). Here you will see the basics of password protecting a directory on your server. You can use any one of the following method:

1. Putting authentication directives in a <Directory> section, in your main server configuration httpd.conf file, is the preferred way to implement this kind of authentication.

2. If you do not have access to Apache httpd.conf file (for example shared hosting) then with the help of file called .htaccess you can create password protect directories. .htaccess file provide a way to make configuration changes on a per-directory basis.

In order to create apache password protected directories you need:

Ø         a password file

Ø         and Directory name which you would like to password protect (/var/www/html/private)

Step 1: Make sure Apache is configured to use .htaccess file

You need to have AllowOverride AuthConfig directive in httpd.conf file in order for these directives to have any effect. Look for DocumentRoot Directory entry. In this example, our DocumentRoot directory is set to /var/www/html/private. Therefore, my entry in httpd.conf looks like as follows:

Options Indexes Includes FollowSymLinks MultiViews

AllowOverride AuthConfig

Order allow,deny

Allow from all

Save the file and restart Apache

# service httpd restart

Step 2: Create a password file with htpasswd

htpasswd command is used to create and update the flat-files (text file) used to store usernames and password for basic authentication of Apache users. General syntax:

# htpasswd -c password-file username

Where,

• -c: Create the password-file. If password-file already exists, it is rewritten and truncated.
• Username: The username to create or update in password-file. If username does not exist in this file, an entry is added. If it does exist, the password is changed.

Create directory outside apache document root, so that only Apache can access password file. The password-file should be placed somewhere not accessible from the web. This is so that people cannot download the password file:

# mkdir -p /home/password/

Add new user called marshal

# htpasswd -c /home/password/.htpasswd marshal

Make sure “/home/password/.htpasswd” file is readable by Apache web server. If Apache cannot read your password file, it will not authenticate you. You need to setup a correct permission using chown command.

Now allow apache user apache to read our password file:

# chown apache:apache /home/password/.htpasswd # chmod 0660 

/home/password/.htpasswd

Create a directory /var/www/html/private if it does not exist:

# mkdir -p /var/www/html/private

Create .htaccess file using text editor:

# cd /var/www/html/private # vi .htaccess

Add following text:

AuthType Basic

AuthName "Restricted Access"

AuthUserFile /home/password/.htpasswd

Require user marshal

Save file and exit to shell prompt.

Step 3: Test your configuration

Fire your browser type url http://yourdomain.com/private or http://localhost/private or http://ip-address/private

When prompted for username and password please supply username marshal and password. You can add following lines to any file <Directory> entry in httpd.conf file:

AuthType Basic

AuthName "Restricted Access"

AuthUserFile /home/password/.htpasswd

Require user marshal

To change or setup new user use htpasswd command again.

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Securing Apache Web Server with Encryption

In this blog we are going to discuss about encrypting communications to web server using TLS/SSL.

Step 1:  Install mod_ssl and httpd

# yum -y install mod_ssl httpd

Step 2: Perform the things required for web server by editing the “/etc/httpd/conf/httpd.conf” and also the creation of web pages in the directories described in the configuration file.

Steps 3: Edit the ssl configuration file

# vim /etc/httpd/conf.d/ssl.conf

Check line number 88

SSLEngine on    ------>>> remove comments if exists

We are using the default certificate and it’s key

Line number 105 pointing to certificate file

SSLCertificateFile /etc/pki/tls/certs/localhost.crt

line nu 112 pointing to certificate key file

SSLCertificateKeyFile /etc/pki/tls/private/localhost.key

Thats all editing the ssl configuration file.

Step 4: Restart httpd service

# service httpd restart

Step 5: Check it out

Open Browser and type the URL in the address bar

http://server.example.com

Now an error message is displayed saying that “this page can only be viewed using the URL “https://server.example.com”. Type the URL

https://server.example.com

When Browser presents a warning,> click the “I understand the Risks” link > click the “Add Exceptions… ” button, > click “View…” when it becomes active. > click “Close”… > click “Confirm security exception”…

Above we used the default certificate / key pair. We too can use a custom self signed certificate using crypto-utils.

Install crypto-utils

# yum -y install crypto-utils

Generate self signed certificate/key pair using “genkey” tool

You should be root to generate a key.

First, use the “cd” command to change to the ”/etc/httpd/conf/” directory. Remove the fake key and certificate that were generated during the installation with the following commands:

# rm ssl.key/server.key rm ssl.crt/server.crt

# genkey www.example.com

 Click next >>

Click next >>

On generating your key, you will be prompted to send a Certificate Request (CSR) to a Certificate Authority (CA).

Click no >>

Click next >>

If you choose to encrypt, you should set a pass phrase to decrypt the key. And also selecting “encrypt the private key”, always you will be asked for the pass phrase whenever restarting the httpd service.

enter the pass phrase and click next >>

Click close.

Now configure the server to use the new certificate and key.

Check whether you have the new certificate and key.

# ls /etc/pki/tls/certs/

ca-bundle.crt  ca-bundle.trust.crt  localhost.crt  make-dummy-cert  

Makefile  server.csr    server.crt    www.example.com.crt

# ls /etc/pki/tls/private/

server.key     www.example.com.key

Edit “/etc/httpd/conf.d/ssl.conf”. Change the SSLCertificateFile and SSLCertificateKey lines to be.

SSLCertificateFile /etc/pki/tls/certs/www.example.com.crt

SSLCertificateKeyFile /etc/pki/tls/private/www.example.com.key

Now restart the httpd service

# service httpd restart

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Configure Apache in RHEL / CENTOS

Packages required	httpd, httpd-devel, httpd-manual
Daemon	/usr/sbin/httpd
Script	/etc/init.d/httpd
Ports	80/tcp (http) , 443/tcp (https)
Configuration	/etc/httpd/* /var/www/*

These are the things to be thought of while setting web server.

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Password protect GRUB / Lock Single User Mode in Linux / RHEL / CENTOS

The primary reasons for password protecting a Linux boot loader are as follows:

1.       Preventing Access to Single User Mode — If attackers can boot the system into single user mode, they are logged in automatically as root without being prompted for the root password.

2.       Preventing Access to the GRUB Console — If the machine uses GRUB as its boot loader, an attacker can use the GRUB editor interface to change its configuration or to gather information using the cat command.

3.       Preventing Access to Insecure Operating Systems — If it is a dual-boot system, an attacker can select an operating system at boot time (for example, DOS), which ignores access controls and file permissions.

How to password protect GRUB

Step 1: Open a shell, login as root, type the following command.

[root@server ~]# /sbin/grub-md5-crypt

Password:

Retype password:

$1$ZqLKR0$cimxs9UxGPM11IG/U.FW41

Once you have confirmed the password, an MD5 hash of the password entered is returned.

Step 2: Edit the GRUB configuration file /boot/grub/grub.conf. Open the file and add the below things just after the timeout line.

 password --md5 <password-hash>

Replace <password-hash> with the value returned by /sbin/grub-md5-crypt

Now the GRUB configuration file will look like this

# grub.conf generated by anaconda

 #

 # Note that you do not have to rerun grub after making changes to this file

 # NOTICE:  You do not have a /boot partition.  This means that

 #          all kernel and initrd paths are relative to /, eg.

 #          root (hd0,0)

 #          kernel /boot/vmlinuz-version ro root=/dev/sda1

 #          initrd /boot/initrd-[generic-]version.img

 #boot=/dev/sda

 default=0

 timeout=5

 password --md5 $1$ZqLKR0$cimxs9UxGPM11IG/U.FW41

 splashimage=(hd0,0)/boot/grub/bootimage1.xpm.gz

 hiddenmenu

 title CentOS (2.6.32-131.21.1.el6.x86_64)

 root (hd0,0)

 kernel /boot/vmlinuz-2.6.32-131.21.1.el6.x86_64 ro root=UUID=7aa8bb3f-2566-4d14-ae10-4d2c24ecbb0a rd_NO_LUKS rd_NO_LVM rd_NO_MD rd_NO_DM LANG=en_US.UTF-8 SYSFONT=latarcyrheb-sun16 KEYBOARDTYPE=pc KEYTABLE=us crashkernel=auto rhgb quiet

 initrd /boot/initramfs-2.6.32-131.21.1.el6.x86_64.img

 title Other

        rootnoverify (hd0,0)

        chainloader +1

Now reboot the system and see the access to the GRUB menu editor or command interface is being locked down. To do so he should press the p followed by the GRUB password. 

Unfortunately, this solution does not prevent an attacker from booting into an insecure operating system in a dual-boot environment. For this, a different part of the /boot/grub/grub.conf file must be edited.

Look for the title line of the operating system that you want to secure. Add the lock directive immediately after it.

For a non Linux system, the stanza will begin like this

title Other lock

Note: A password line must be present in the main section of the /boot/grub/grub.conf file for this method to work properly. Otherwise, an attacker can access the GRUB editor interface and remove the lock line.

Also you can set different passwords of each kernel or operating system you have.For this you have to add lockline to that particular stanza followed by a password line.

title Other lock password --md5 <password-hash>

Replace <password-hash> with the value returned by /sbin/grub-md5-crypt

Now the kernel or the operating system part with password protected in the GRUB configuration file will look like this.

title Other lock password --md5 $1$rjTKR0$GzSI4M.q8EREUsAw674Z5/

        rootnoverify (hd0,0)

        chainloader +1

That’s it….

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Change / Hack the Root password in Linux / RHEL / CENTOS

Forgot root password

Suppose you want to get into a Linux system. You know nothing about the existing user’s or their passwords. You have no idea about these things. Then what will you do??
The only thing you know that the user root exists. So we must find a way to get the root’s password.

I think you know about the different run-levels on a UNIX machine. The single user mode or the run-level 1 is used for these kind of rescue purposes. So what you should do is to enter the rescue mode. Click here to learn How to enter Rescue mode in Linux / UNIX.

Once the Rescue environment is loaded, you will get a shell which is your default bash shell.

Now use the passwd command to set / change the root’s password.

[root@server ~]# Passwd

Changing password for user root

New password:

BAD PASSWORD: it is too simplistic/systematic

Retype new password:

Passwd: all authentication tokens updated successfully.

Now the password has been changed the newly set one.

Note:
If you are using Red Hat Enterprise Linux 6, a security bug was there which blocked the passwd command from working in single user mode. Later this was fixed by a bug fix update (http://rhn.redhat.com/errata/RHBA-2010-0845.html).

If you have installed the original selinux-policy package, the passwd command might not run. So make the SELinux policy to permissive for the passwd command to run.

Get the SELinux status by,

# getenforce Enforcing

Now change to permissive by,

# setenforce 0

Again check the status and see the change

# getenforce Permissive

Now run the passwd command and after that change the SELinux back to the Enforcing state by the

# setenforce 1

# getenforce Enforcing

Now reboot the machine and boot normally.

That’s all you are done.

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Swap Space in Linux / RHEL / CENTOS / Fedora

What is a Swap space?

• Swap space is hard disk space that extends system RAM.

Swap space or virtual memory is hard disk space that acts as an extension of system RAM. Of course, due to the relative differential in data access on RAM versus hard disk, we prefer not to use swap space if it can be avoided. Nonetheless, it is vital to the proper functioning of a typical Linux system that some swap space be made available.

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