Difference between RHEL6 & RHEL7 and Features of RHEL7

Features	RHEL 7	RHEL 6
Default File System	XFS	EXT4
Kernel Version	3.10.x-x kernel	2.6.x-x Kernel
Kernel Code Name	Maipo	Santiago
General Availability Date of First Major Release	2014-06-09 (Kernel Version 3.10.0-123)	2010-11-09 (Kernel Version 2.6.32-71)
First Process	systemd (process ID 1)	init (process ID 1)
Runlevel	runlevels are called as "targets" as shown below: runlevel0.target -> poweroff.target runlevel1.target -> rescue.target runlevel2.target -> multi-user.target runlevel3.target -> multi-user.target runlevel4.target -> multi-user.target runlevel5.target -> graphical.target runlevel6.target -> reboot.target /etc/systemd/system/default.target (this by default is linked to the multi-user target)	Traditional runlevels defined : runlevel 0 runlevel 1 runlevel 2 runlevel 3 runlevel 4 runlevel 5 runlevel 6 and the default runlevel would be defined in /etc/inittab file. /etc/inittab
Host Name Change	In Red Hat Enterprise Linux 7, as part of the move to the new init system (systemd), the hostname variable is defined in /etc/hostname.	In Red Hat Enterprise Linux 6, the hostname variable was defined in the /etc/sysconfig/network configuration file.
Max Supported File Size	Maximum (individual) file size = 500TB  Maximum filesystem size = 500TB (This maximum file size is only on 64-bit machines. Red Hat Enterprise Linux does not support XFS on 32-bit machines.)	Maximum (individual) file size = 16TB  Maximum filesystem size = 16TB (This maximum file size is based on a 64-bit machine. On a 32-bit machine, the maximum files size is 8TB.)
File System Check	"xfs_repair" XFS does not run a file system check at boot time.	"e2fsck" File system check would gets executed at boot time.
Differences Between xfs_repair & e2fsck	"xfs_repair" - Inode and inode blockmap (addressing) checks. - Inode allocation map checks. - Inode size checks. - Directory checks. - Pathname checks. - Link count checks. - Freemap checks. - Super block checks.	"e2fsck" - Inode, block, and size checks. - Directory structure checks. - Directory connectivity checks. - Reference count checks. - Group summary info checks.
Change In File System Structure	/bin, /sbin, /lib, and /lib64 are now nested under /usr.	/bin, /sbin, /lib, and /lib64 are usually under /
Boot Loader	GRUB 2 Supports GPT, additional firmware types, including BIOS, EFI and OpenFirmwar. Ability to boot on various file systems (xfs, ext4, ntfs, hfs+, raid, etc)	GRUB 0.97
KDUMP	RHEL7 supports kdump on large memory based systems up to 3 TB	Kdump doesn’t work properly with large RAM based systems.
System & Service Manager	"Systemd" systemd is a system and service manager for Linux, and replaces SysV and Upstart used in previous releases of Red Hat Enterprise Linux. systemd is compatible with SysV and Linux Standard Base init scripts.	Upstart
Enable/Start Service	For RHEL 7, the systemctl command replaces service and chkconfig. - Start Service : "systemctl start nfs-server.service". - Enable Service : To enable the service (example: nfs service ) to start automatically on boot : "systemctl enable nfs-server.service". Although one can still use the service and chkconfig commands to start/stop and enable/disable services, respectively, they are not 100% compatible with the RHEL 7 systemctl command (according to redhat).	Using "service" command and "chkconfig" commands. - Start Service : "service start nfs" OR "/etc/init.d/nfs start" - Enable Service : To start with specific runlevel : "chkconfig --level 3 5 nfs on"
Default Firewall	"Firewalld (Dynamic Firewall)" The built-in configuration is located under the /usr/lib/firewalld directory. The configuration that you can customize is under the /etc/firewalld directory. It is not possible to use Firewalld and Iptables at the same time. But it is still possible to disable Firewalld and use Iptables as before.	Iptables
Network Bonding	"Team Driver" -/etc/sysconfig/network-scripts/ifcfg-team0 - DEVICE=”team0” - DEVICETYPE=”Team”	"Bonding" -/etc/sysconfig/network-scripts/ifcfg-bond0 - DEVICE=”bond0”
Network Time Synchronization	Using Chrony suite (faster time sync compared with ntpd)	Using ntpd
NFS	NFS4.1 NFSv2 is no longer supported. Red Hat Enterprise Linux 7 supports NFSv3, NFSv4.0, and NVSv4.1 clients.	NFS4
Cluster Resource Manager	Pacemaker	Rgmanager
Load Balancer Technology	Keepalived and HAProxy	Piranha
Desktop/GUI Interface	GNOME3 and KDE 4.10	GNOME2
Default Database	MariaDB is the default implementation of MySQL in Red Hat Enterprise Linux 7	MySQL

RHEL 7 Extra Features

Introduction of Docker 

Docker is an open source project that automates the deployment of applications inside Linux Containers, and provides the capability to package an application with its runtime dependencies into a container.

Device Hotplug Removed

While RHEL 5/6 has device hotplug support (udev rule that runs the ifup script for newly created devices), it has been disabled for RHEL 7 since it can result in race conditions when initializing newly found.

No 32 Bit ISO Image

No 32 bit ISO for download. Red Hat Enterprise Linux 7 will only provide 64-bit ISO's, thus allowing only a 64-bit operating environment. RHEL 7 will not natively support 32-bit hardware.

MemAvailable Added to meminfo

A new entry to the /proc/meminfo file has been introduced to provide the MemAvailable field. MemAvailable provides an estimate of how much memory is available for starting new applications, without swapping. However, unlike the data provided by the Cache or Free fields, MemAvailable takes into account page cache and also that not all reclaimable memory slabs will be reclaimable due to items being in use.

New Ruby and Python Versions

Red Hat Enterprise Linux 7 provides the latest Ruby version, 2.0.0 and Python 2.7.5.

OpenJDK7 Made Default

Red Hat Enterprise Linux 7 features OpenJDK7 as the default Java Development Kit (JDK) and Java 7 as the default Java version.

More Powerful NetworkManager          

NetworkManager has been significantly enhanced to configure and monitor all the networking features for enterprise class servers and for desktop applications.

For the enterprise data centers, NetworkManager can be used for tasks such as basic networking configuration, network teaming, configuring virtual LANs, bridges, bonds, IPv6, VPNs, assigning interfaces to firewall zones, and others. For desktop servers it can manage wired and wireless networks and VPNs.

Support for 40 Gigabit NICs

Red Hat Enterprise Linux 7 supports 40 Gigabit network interface controllers (NICs) from multiple hardware partners. This provides support for 40 Gigabit Ethernet link speeds enabling faster network communication for applications and systems. Note that the ethtool utility will report interface link speeds up to 40Gb data rates.

OpenSSH - Multiple Required Authentications

Red Hat Enterprise Linux 7 supports multiple required authentications in SSH protocol version 2 using the AuthenticationMethods option. This option lists one or more comma-separated lists of authentication method names. Successful completion of all the methods in any list is required for authentication to complete.

Minimum Disk Space for Installation of RHEL7

Red Hat Enterprise Linux 7 now requires at least 1 GB of disk space to install. However, Red Hat recommends a minimum of 5 GB of disk space for all supported architectures.

Implementation of tmpfs file system

Red Hat Enterprise Linux 7 offers the ability to use /tmp as a mount point for a temporary file storage system (tmpfs).

When enabled, this temporary storage appears as a mounted file system, but stores its content in volatile memory instead of on a persistent storage device. No files in /tmp are stored on the hard drive except when memory is low, in which case swap space is used. This means that the contents of /tmp are not persisted across a reboot.

New Logging Framework

Red Hat Enterprise Linux 7 introduces a new logging daemon, journald, as part of the move to systemd.

journald captures the following types of message for all services:

- syslog messages

- kernel messages

- initial RAM disk and early boot messages

- messages sent to standard output and standard error output.

Changes to mount options

Unlike ext3 and ext4, the XFS file system enables the user_xattr and acl mount options by default. Ext3 and ext4 file systems do not enable these attributes by default.

Reference: http://simplylinuxfaq.blogspot.in/p/major-difference-between-rhel-7-and-6.html