Change default runlevel in CentOS 7 / RHEL 7 | GUI | NON-GUI

Hello All,

As systemd is already implemented in CentOS 7 and RHEL 7, Method has been changed to change runlevel in Red Hat Enterprise Linux and CentOS 7. So sharing method to change runlevel in CentOS and RHEL 7

 

CentOS / RHEL 7
CentOS / RHEL 7

Please perform following simple steps to change runlevel from GUI to NON-GUI and NON-GUI to GUI.

1. Execute following command to check current runlevel settings.

[root@tejasbarot ~]# systemctl get-default

1.1 If current setting is graphical.target then Linux will boot in GUI Mode.
1.2 If current setting is multi-user.target then Linux will boot in NON-GUI Mode.

2. Execute following command to Change from GUI to NON-GUI Mode.

[root@tejasbarot ~]# systemctl set-default multi-user.target
[root@tejasbarot ~]# reboot

3. Execute following command to Change from NON-GUI to GUI Mode.

[root@tejasbarot ~]# systemctl set-default graphical.target
[root@tejasbarot ~]# reboot

Hope it will helps you.

Enjoy Linux 🙂 Enjoy Open Source 🙂

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Linux: The GHOST Vulnerability | RHEL | CentOS

The GHOST vulnerability is a serious weakness in the Linux glibc library. It allows attackers to remotely take complete control of the victim system without having any prior knowledge of system credentials. CVE-2015-0235 has been assigned to this issue.

 

Qualys security researchers discovered this bug and worked closely with Linux distribution vendors. And as a result of that we are releasing this advisory today as a co-ordinated effort, and patches for all distribution are available January 27, 2015.

 

What is glibc?

The GNU C Library or glibc is an implementation of the standard C library and a core part of the Linux operating system. Without this library a Linux system will not function.

 

What is the vulnerability?

During a code audit Qualys researchers discovered a buffer overflow in the __nss_hostname_digits_dots() function of glibc. This bug can be triggered both locally and remotely via all the gethostbyname*() functions. Applications have access to the DNS resolver primarily through the gethostbyname*() set of functions. These functions convert a hostname into an IP address.

 

Ghost Vulnerability
Ghost Vulnerability

 

 

What is the risk?

There is a remote code execution risk due to this vulnerability. An attacker who exploits this issue can gain complete control of the compromised system.

 

Is the risk real?

During our testing, we developed a proof-of-concept in which we send a specially created e-mail to a mail server and can get a remote shell to the Linux machine. This bypasses all existing protections (like ASLR, PIE and NX) on both 32-bit and 64-bit systems.

 

What can be done to mitigate the risk?

The best way to mitigate the risk is to apply a patch from your Linux vendor. Qualys has worked closely with Linux distribution vendors and patches are available as of today January 27, 2015.

 

Why is it called the GHOST vulnerability?

It is called as the GHOST vulnerability as it can be triggered by the GetHOST functions.

 

Is this a design flaw?

No. This is an implementation problem in the affected versions of the software.

 

What versions and operating systems are affected?

The first vulnerable version of the GNU C Library affected by this is glibc-2.2, released on November 10, 2000. We identified a number of factors that mitigate the impact of this bug. In particular, we discovered that it was fixed on May 21, 2013 (between the releases of glibc-2.17 and glibc-2.18). Unfortunately, it was not recognized as a security threat; as a result, most stable and long-term-support distributions were left exposed including Debian 7 (wheezy), Red Hat Enterprise Linux 6 & 7, CentOS 6 & 7, Ubuntu 12.04, for example.

 

Where can I download the exploit?

We want to give everyone enough time to patch. According to our data once the vulnerability has reached its half-life we will release the exploit. Half-life is the time interval measuring a reduction of a vulnerability’s occurrence by half. Over time, this metric shows how successful efforts have been to eradicate vulnerability. A shorter half-life indicates faster remediation. Half-life was originally coined by Qualys in the Laws of Vulnerability.

 

Qualys customers can detect GHOST by scanning with the Qualys Vulnerability Management (VM) cloud solution as QID 123191. This means that Qualys customers can get reports detailing their enterprise-wide exposure during their next scanning cycle, which allows them to get visibility into the impact within their organization and efficiently track the remediation progress of this serious vulnerability.

 

References:

Qualys Advisory: https://www.qualys.com/research/security-advisories/GHOST-CVE-2015-0235.txt

RedHat: https://rhn.redhat.com/errata/RHSA-2015-0090.html

Ubuntu: https://launchpad.net/ubuntu/+source/eglibc

Debian: https://security-tracker.debian.org/tracker/CVE-2015-0235

Oracle Enterprise Linux: https://oss.oracle.com/pipermail/el-errata/2015-January/004810.html

CentOS: http://lists.centos.org/pipermail/centos-announce/2015-January/020906.html

OpenSUSE: http://lists.opensuse.org/opensuse-updates/2015-01/msg00085.html

GNU C Library: http://www.gnu.org/software/libc/

Mitre: http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2015-0235

Link to Original Article : https://community.qualys.com/blogs/laws-of-vulnerabilities/2015/01/27/the-ghost-vulnerability

Hope this will be helpful to you all.

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SAR GUI: Export sar / sysstat reports as PDF using kSar

Hello,

If you are Linux Administrator you must know what SAR is, sar is a very useful utility for Linux Administrators to get the report of CPU Usage and You can monitor I/O, CPU Usage, Idle system state using sar utility. This article will help you to read / export sar reports in Graphical mode.

In this HowTo, I will show you how you can export sar reports as PDF / JPG / PNG using kSar tool.

ksar - PDF
ksar – PDF

In RHEL / CentOS you will find sar reports under /var/log/sa

In Ubuntu / Debian based Linux you will find sar reports under /var/log/sysstat

Perform following steps to export sar report:

1. Make Sure Java is installed on your system to open kSar Utility.

2. Download kSar Utility from below URL

http://sourceforge.net/projects/ksar/

3. Extract / Unzip Downloaded ksar-x-x-x.zip file

root@tejas-barot-linux-ahmedabad:~/Downloads# unzip kSar-5.0.6.zip

4. Give Executable permission to kSar.jar

root@tejas-barot-linux-ahmedabad:~/Downloads/kSar-5.0.6# chmod +x kSar.jar

5. Execute below command to open java file (kSar.jar):

root@tejas-barot-linux-ahmedabad:~/Downloads/kSar-5.0.6# java -jar kSar.jar

6. Now Click on Data -> Load from Text file…

7. Provide Path of sar reports path:

For RHEL: /var/log/sa/sarXX
For Debian/Ubuntu: /var/log/sysstat/sarXX

8. Select “Export to PDF / JPG / PNG” from Data  To Export sar report as PDF / JPG / PNG

Enjoy Sysstat Monitoring 🙂 Enjoy GUI Reports 🙂 Enjoy Linux 🙂 Enjoy Open Source 🙂

This is how you can export sar reports in Graphical format.

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RHEL 7 / CentOS 7 / Grub2 : Protect Single User Mode / Rescue / Emergency with Password

Hello All,

As we all know Red Hat Enterprise Linux 7 and CentOS 7 Linux is out now, Recently I have posted How to enter into Single User Mode / Rescue / Emergency Mode on RHEL 7 / CentOS 7.

This post is to Secure Single User Mode / Rescue Mode / Emergency mode on RHEL 7 / CentOS 7 in Grub2, By performing this Article you will able to secure your Grub2 Edits with Username and Password, It is always a good idea to protect your Grub2.

In This Howto, We will protect Grub2 with Encrypted Password and Plain Password.

To Follow this how to make sure you have root password to make changes in Grub2, Please make sure you are doing exact as per instructions and going through notes.

Do this on your own risk, You will be the only responsible if anything goes wrong in any case 🙂

 

CentOS7_Grub2
CentOS7_Grub2

 

Protect Grub2 with Plain Password Method

1. Login as a root user or user with rights to edit grub2 configuration file (sudo).

[tejas-barot@rhel-centos7-tejas-barot-linux ~]$ su -

2. Make a backup of existing grub.cfg and default /etc/grub.d/10_linux so if anything goes wrong we can always restore it.

[root@rhel-centos7-tejas-barot-linux ~]# cp /boot/grub2/grub.cfg /boot/grub2/grub.cfg.orig
[root@rhel-centos7-tejas-barot-linux ~]# cp /etc/grub.d/10_linux /etc/grub.d/10_linux.orig

3. Now, Adding Entries to protect Grub2 with username and password:

Note1: Replace Username and Password from below lines and Add below lines at last in file /etc/grub.d/10_linux

Note2: Make sure you don’t insert following entries multiple time.

[root@rhel-centos7-tejas-barot-linux ~]# vi /etc/grub.d/10_linux
cat << EOF
set superusers="tejasbarot" password tejasbarot alub@123
EOF

4. Now let us Generate New grub.cfg, Execute following command.

[root@rhel-centos7-tejas-barot-linux ~]# grub2-mkconfig --output=/tmp/grub2.cfg

5. Now Replace this New configured grub2.cfg with existing grub2.cfg

[root@rhel-centos7-tejas-barot-linux ~]# mv /boot/grub2/grub.cfg /boot/grub2/grub.cfg.move
[root@rhel-centos7-tejas-barot-linux ~]# mv /tmp/grub2.cfg /boot/grub2/grub.cfg

6. That’s It, Now You can reboot and Press “e” on Grub Menu, It will ask you for the password.

Protect Grub2 with Password Encrypted Method

1. Login as a root user or user with rights to edit grub2 configuration file (sudo).

[tejas-barot@rhel-centos7-tejas-barot-linux ~]$ su -

2. Make a backup of existing grub.cfg and default /etc/grub.d/10_linux so if anything goes wrong we can always restore it.

[root@rhel-centos7-tejas-barot-linux ~]# cp /boot/grub2/grub.cfg /boot/grub2/grub.cfg.orig
[root@rhel-centos7-tejas-barot-linux ~]# cp /etc/grub.d/10_linux /etc/grub.d/10_linux.orig

3. Let’s Generate Encrypted password with “grub2-mkpasswd-pbkdf2”, Once you will execute below command it will ask you for the password, Please enter password twice, It will generate password string which you need to add to 10_linux file. ( Shortened version of string, You will have to paste complete string )

[root@rhel-centos7-tejas-barot-linux ~]# grub2-mkpasswd-pbkdf2
Enter Password:
Reenter Password:
PBKDF2 hash of your password is grub.pbkdf2.sha512.10000.F1C4CFAA5A51EED123BE8238C23B25B2A6909AFC9812F0D45

4. Now, Adding Entries to protect Grub2 with username and password:

Note1: Replace Username and Password from below lines and Add below lines at last in file /etc/grub.d/10_linux

Note2: Make sure you don’t insert following entries multiple time.

Note3: Here I have added Short String for example, you will have to add full string to make it work.

[root@rhel-centos7-tejas-barot-linux ~]# vi /etc/grub.d/10_linux
cat << EOF
set superusers="tejasbarot" password_pbkdf2 tejasbarot grub.pbkdf2.sha512.10000.F1C4CFAA5A51EED123BE8238C23B25B2A6909AFC9812F0D45
EOF

5. Now let us Generate New grub.cfg, Execute following command.

[root@rhel-centos7-tejas-barot-linux ~]# grub2-mkconfig --output=/tmp/grub2.cfg

6. Now Replace this New configured grub2.cfg with existing grub2.cfg

[root@rhel-centos7-tejas-barot-linux ~]# mv /boot/grub2/grub.cfg /boot/grub2/grub.cfg.move
[root@rhel-centos7-tejas-barot-linux ~]# mv /tmp/grub2.cfg /boot/grub2/grub.cfg

7. That’s It, Now You can reboot and Press “e” on Grub Menu, It will ask you for the password.

Enjoy Protected Grub2 🙂 Enjoy CentOS 7 🙂 Enjoy RHEL 7 🙂 Enjoy Linux 🙂 Enjoy Open Source 🙂

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RHEL 7 / CentOS 7 : Single User Mode / Recovering / Reset Root Password

Hello,
Setting up the root password is a mandatory part of the Red Hat Enterprise Linux 7 / CentOS 7installation.
If you forget or lose your password, it is possible to reset it. Now it is known as Rescue Mode / Emergency mode in CentOS / RHEL 7, Previously in RHEL / CentOS 5/6 It was “Single User Mode”.
Note: In GRUB 2, resetting the password is no longer performed in single-user mode as it was in GRUB included in Red Hat Enterprise Linux 6. The root password is now required to operate in single-user mode as well as in emergency mode.
systemd_recover_root_password
systemd_recover_root_password
Process: Resetting the Root Password
  1. Please follow this procedure carefully, any mistake can make your system / Linux unstable, Perform this own your on risk.
    q
  2. Start the system and, on the GRUB 2 boot screen, press the e key for edit.
  3. Add the following parameter at the end of the linux line, or linuxefi on UEFI systems (In case of  VMWare like KVM or VirtualBox use rb.break instead of init=/bin/sh):
    init=/bin/sh
    The Linux kernel will run the /bin/sh shell rather than the system init daemon. Therefore, some functions may be limited or missing.

    Important

    The rhgb and quiet parameters must be disables in order to enable system messages.
  4. Press Ctrl+x to boot the system with the parameter.
    The shell prompt appears.
  5. The file system is mounted read-only. You will not be allowed to change the password if the file system is not writable.
    To remount the file system as writable, run the mount -o remount, rw / command.
  6. Run the passwd command and follow the instructions displayed on the command line to change the root password.
    Note that if the system is not writable, the passwd tool fails with the following error:
    Authentication token manipulation error
  7. To make sure that SELinux context of the files that were modified is restored properly after boot, run
    touch /.autorelabel
  8. Run the exec /sbin/init command to resume the initialization and finish the system boot.
    Running the exec command with another command specified replaces the shell and creates a new process; init in this case.
    Alternatively, if you wish to reboot the system, run the exec /sbin/reboot command instead.

Enjoy RHEL 7 🙂 Enjoy CentOS 7 🙂 Enjoy Linux 🙂 Enjoy Open Source 🙂

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RHEL 7 / CentOS 7: How to get started with Firewalld

Hello All,

Today I was trying to learn and know about Systemd. I have found one of the great Article about firewalld, Sharing with you guys, It will help you to understand this biggest and major change in RHEL and CentOS 7.

This article is not mine, I found on internet and felt that this is wonderful Article so Sharing with you all, Thanks to Original author, Given credit to him at the end of article.

firewalld
firewalld

Presentation

Firewalld is the new userland interface in RHEL 7. It replaces the iptables interface and connects to the netfilter kernel code. It mainly improves the security rules management by allowing configuration changes without stopping the current connections.

To know if Firewalld is running, type:

# systemctl status firewalld
firewalld.service - firewalld - dynamic firewall daemon
   Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled)
   Active: active (running) since Tue 2014-06-17 11:14:49 CEST; 5 days ago
   ...

or alternatively:

# firewall-cmd --state
running

Note: If Firewalld is not running, the command displays not running.

If you’ve got several network interfaces in IPv4, you will have to activate ip_forwarding.
To do that, paste the following line in the /etc/sysctl.conf file:

net.ipv4.ip_forward=1

Then, activate the configuration:

# sysctl -p

Although Firewalld is the RHEL 7 way to deal with firewalls and provides many improvements, iptables can still be used.

Zone management

Also, a new concept of zone appears : all network interfaces can be located in the same default zone or divided into different ones according to the levels of trust defined.

To get the default zone, type:

# firewall-cmd --get-default-zone
public

To get the list of zones where you’ve got network interfaces assigned to, type:

# firewall-cmd --get-active-zones
public
interfaces: eth0

To get the list of all the available zones, type:

# firewall-cmd --get-zones
block dmz drop external home internal public trusted work

To get all the details about the public zone, type:

# firewall-cmd --zone=public --list-all
public (default, active)
  interfaces: eth0
  sources: 
  services: dhcpv6-client ssh
  ports: 
  masquerade: no
  forward-ports: 
  icmp-blocks: 
  rich rules: 

To change the default zone to home permanently, type:

# firewall-cmd --set-default-zone=home
success

Network interfaces can be assigned to a zone in a temporary (until the next reboot or reload) or permanent way.

To assign the eth0 network interface temporary to the internal zone, type:

# firewall-cmd --zone=internal --change-interface=eth0
success

To assign the eth0 network interface permanently to the internal zone (a file called internal.xml is created in the /etc/firewalld/zones directory), type:

# firewall-cmd --permanent --zone=internal --change-interface=eth0
success

To know which zone is associated with the eth0 interface, type:

# firewall-cmd --get-zone-of-interface=eth0
internal

Service management

After assigning each network interface to a zone, it is now possible to add services to each zone.
To allow the http service permanently in the internal zone, type:

# firewall-cmd --permanent --zone=internal --add-service=http
success
# firewall-cmd --reload

Note1: Type –remove-service=http to deny the http service.
Note2: The firewall-cmd –reload command is necessary to activate the change. Contrary to the –complete-reload option, current connections are not stopped.

To get the list of services in the default zone, type:

# firewall-cmd --list-services
dhcpv6-client ssh

Note: To get the list of the services in a particular zone, add the –zone= option.

Service firewall configuration

With the Firewalld package, the firewall configuration of the main services (ftp, httpd, etc) comes in the /usr/lib/firewalld/services directory. But it is still possible to add new ones in the /etc/firewalld/services directory. Also, if files exist at both locations for the same service, the file in the /etc/firewalld/services directory takes precedence.

For example, it is the case of the HAProxy service. There is no firewall configuration associated.
Create the /etc/firewalld/services/haproxy.xml and paste the following lines:

<?xml version="1.0" encoding="utf-8"?>
<service>
 <short>HAProxy</short>
 <description>HAProxy load-balancer</description>
 <port protocol="tcp" port="80"/>
</service>

Assign the correct SELinux context and file permissions to the haproxy.xml file:

# cd /etc/firewalld/services
# restorecon haproxy.xml
# chmod 640 haproxy.xml

Add the HAProxy service to the default zone permanently and reload the firewall configuration:

# firewall-cmd --permanent --add-service=haproxy
# firewall-cmd --reload

Port management

Port management follows the same model as service management.

To allow the 443/tcp port temporary in the internal zone, type:

# firewall-cmd --zone=internal --add-port=443/tcp
success
# firewall-cmd --reload

Note: type –remove-port=443/tcp to deny the port.

To get the list of ports open in the internal zone, type:

# firewall-cmd --zone=internal --list-ports
443/tcp

Masquerading

If your firewall is your network gateway and you don’t want everybody to know your internal addresses, you can set up two zones, one called internal, the other external, and configure masquerading on the external zone. This way, all packets will get your firewall ip address as source address.

To set up masquerading on the external zone, type:

# firewall-cmd --zone=external --add-masquerade

Note1: To remove masquerading, use the –remove-masquerade option.
Note2: To know if masquerading is active in a zone, use the –query-masquerade option.

Port forwarding

In addition to the masquerading, you can want to use port forwarding.
If you want all packets intended for port 22 to be now forwarded to port 3753, type:

# firewall-cmd --zone=external --add-forward-port=port=22:proto=tcp:toport=3753

Note1: To remove port forwarding, use the –remove-forward-port option.
Note2: To know if port forwarding is active in a zone, use the –query-forward-port option.
Also, if you want to define the destination ip address, type:

# firewall-cmd --zone=external --add-forward-port=port=22:proto=tcp:toport=3753:toaddr=10.0.0.1

Direct rules

It is still possible to set specific rules by using the direct mode (here to open the tcp port 9000) that by-passes the Firewalld interface:

# firewall-cmd --direct --add-rule ipv4 filter INPUT 0 -p tcp --dport 9000 -j ACCEPT
success
# firewall-cmd --reload

Note: This last example has been borrowed from Khosro Taraghi’s blog.

To display all the direct rules added, type:

# firewall-cmd --direct --get-all-rules

In addition, you can read this very good article about Firewalld by Sander van Vugt.

Thanks to Original Author for explaining it very nicely.

Source : http://www.certdepot.net/rhel7-get-started-firewalld/

Enjoy Firewalld 🙂 Enjoy Systemd 🙂 Enjoy RHEL 7 🙂 Enjoy CentOS 7 🙂 Enjoy Open Source 🙂

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RHEL 7 / CentOS 7 : Disable Firewalld and use iptables

Hello,

Just installed CentOS 7 on my Virtual machine and realized that, Firewalld is bit complicated as I am using iptables firewall from many years. So decided not to use firewalld at least as of now and wanted to continue with iptables commands as I was using in RHEL / CentOS 5 and 6.

I thought iptables will not be there and I will have to deal with firewalld but a little small trick in RHEL7 takes me to the solution which I wanted and I found that I can still use the iptables by disabling firewalld service.

So, If you are in same condition as mine and you want to use iptables on CentOS / RHEL 7 instead of firewalld, Please follow this howto.

Firewall
Firewall

As we all know that, CentOS / RHEL 7 both are completely systemd based, So We will have to use few systemd related commands to disable firewalld and enable iptables service.

1. Disable Firewalld Service.

[root@rhel-centos7-tejas-barot-linux ~]# systemctl mask firewalld

2. Stop Firewalld Service.

[root@rhel-centos7-tejas-barot-linux ~]# systemctl stop firewalld

3. Install iptables service related packages.

[root@rhel-centos7-tejas-barot-linux ~]# yum -y install iptables-services

4. Make sure service starts at boot:

[root@rhel-centos7-tejas-barot-linux ~]# systemctl enable iptables

# If you do not want ip6tables, You can skip following command.

[root@rhel-centos7-tejas-barot-linux ~]# systemctl enable ip6tables

5. Now, Finally Let’s start the iptables services.

[root@rhel-centos7-tejas-barot-linux ~]# systemctl start iptables

# If you do not want ip6tables, You can skip following command.

[root@rhel-centos7-tejas-barot-linux ~]# systemctl start ip6tables

Firewalld Service is now disabled and stop, You can use iptables.

Now, You will be able to use iptables as your firewall, You can add / remove rules as you were doing in previous releases of Red Hat / CentOS 5 and 6, You can configure firewall with iptables in same manner as previous.

Enjoy Linux 🙂 Enjoy Firewall 🙂 Enjoy iptables 🙂 Enjoy ip6tables 🙂 Enjoy FirewallD 🙂 Enjoy CentOS 7 🙂 Enjoy RHEL 7 🙂 Enjoy Open Source

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Information on Red Hat Certification / RHCE / RHEV / Red Hat OpenStack / RHEL 7

Hello Friends,

Certification
Certification

RHEL 7 is released, I am getting constant calls / emails / messages from many friends from different different places regarding their doubts on RHEL 5 to 6 or 6 to 7 up-gradation.

Sharing this to clear confusion / doubts.

Clear your doubts Regarding Up-gradation :-

1. Yes, RHEL 7 is out, but There is no compulsion or Mandatory from Red Hat to Upgrade your certificate from RHEL 5 to 6 or RHEL 6 to 7. Its not mandatory at all, It is all up to you.

2. Whether its RHEL 6 release or RHEL 7 release, If you are RHCE then Do not worry, Your Certificate is not going to expire. There is nothing like “expiry” in RHCE certificate, You will be still known as “Red Hat Certified Engineer” but the only difference is you will be known as “RHCE from non-current Version”.

3. RHCE Certificate / exam is not mandatory for Red Hat Enterprise Virtualization. You can give direct exam of RHEV.

4. Same in this case, RHCE Certificate / exam is not mandatory for RedHat OpenStack exam. You can give direct exam of Red Hat OpenStack.

I was getting lots of calls / emails / messages regarding these queries to help them out, I have shared this here so even if some friends from here are having same queries/doubts/confusion, So it will get cleared.

Correct me if I am wrong.

Hope this will helps you.

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