Difference between RHEL 6.x and RHEL 7.x

Features	RHEL 6	RHEL 7
Default File System	EXT4	XFS
Kernel Version	2.6.x-x Kernel	3.10.x-x kernel
Kernel Code Name	Santiago	Maipo
General Availability Date of First Major Release	2010-11-09 (Kernel Version 2.6.32-71)	2014-06-09 (Kernel Version 3.10.0-123)
First Process	init (process ID 1)	systemd (process ID 1)
Runlevel	Traditional runlevels defined :	runlevels are called as "targets" as shown below:
	runlevel 0	runlevel0.target -> poweroff.target
	runlevel 1	runlevel1.target -> rescue.target
	runlevel 2	runlevel2.target -> multi-user.target
	runlevel 3	runlevel3.target -> multi-user.target
	runlevel 4	runlevel4.target -> multi-user.target
	runlevel 5	runlevel5.target -> graphical.target
	runlevel 6	runlevel6.target -> reboot.target
	and the default runlevel would be defined in /etc/inittab file.	/etc/systemd/system/default.target (this by default is linked to the multi-user target)
	/etc/inittab
Host Name Change	In Red Hat Enterprise Linux 6, the hostname variable was defined in the /etc/sysconfig/network configuration file.	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.
Change In UID Allocation	Default UID assigned to users would start from 500.	By default any new users created would get UIDs assigned starting from 1000.
		This could be changed in /etc/login.defs if required.
	This could be changed in /etc/login.defs if required.
Max Supported File Size	Maximum (individual) file size = 16TB	Maximum (individual) file size = 500TB
	Maximum filesystem size = 16TB	Maximum filesystem size = 500TB
	(This maximum file size is based on a 64-bit machine. On a 32-bit machine, the maximum files size is 8TB.)	(This maximum file size is only on 64-bit machines. Red Hat Enterprise Linux does not support XFS on 32-bit machines.)
File System Check	"e2fsck"	"xfs_repair"
	File system check would gets executed at boot time.	XFS does not run a file system check at boot time.
Differences Between xfs_repair & e2fsck
	"e2fsck"	"xfs_repair"
	- Inode, block, and size checks.	- Inode and inode blockmap (addressing) checks.
		- Inode allocation map checks.
	- Directory structure checks.	- Inode size checks.
		- Directory checks.
	- Directory connectivity checks.	- Pathname checks.
		- Link count checks.
	- Reference count checks.	- Freemap checks.
		- Super block checks.
	- Group summary info checks.
Difference Between xfs_growfs & resize2fs	"resize2fs"	"xfs_growfs"
	resize2fs takes logical volume name as arguments.	xfs_growfs takes mount point as arguments.
Change In File System Structure	/bin, /sbin, /lib, and /lib64 are usually under /	/bin, /sbin, /lib, and /lib64 are now nested under /usr.
Boot Loader	GRUB 0.97	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)
KDUMP	Kdump doesn’t work properly with large RAM based systems.	RHEL7 supports kdump on large memory based systems up to 3 TB
System & Service Manager	Upstart	"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.
Enable/Start Service	Using "service" command and "chkconfig" commands.	For RHEL 7, the systemctl command replaces service and chkconfig.
	- Start Service : "service start nfs" OR "/etc/init.d/nfs start"	- Start Service : "systemctl start nfs-server.service".
	- Enable Service : To start with specific runlevel : "chkconfig --level 3 5 nfs on"	- 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).
Default Firewall	Iptables	"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.
Network Bonding	"Bonding"	"Team Driver"
	-/etc/sysconfig/network-scripts/ifcfg-bond0	-/etc/sysconfig/network-scripts/ifcfg-team0
	- DEVICE=”bond0”	- DEVICE=”team0”
		- DEVICETYPE=”Team”
Network Time Synchronization	Using ntpd	Using Chrony suite (faster time sync compared with ntpd)
NFS	NFS4	NFS4.1
		NFSv2 is no longer supported. Red Hat Enterprise Linux 7 supports NFSv3, NFSv4.0, and NVSv4.1 clients.
Cluster Resource Manager	Rgmanager	Pacemaker
Load Balancer Technology	Piranha	Keepalived and HAProxy
Desktop/GUI Interface	GNOME2	GNOME3 and KDE 4.10
Default Database	MySQL	MariaDB is the default implementation of MySQL in Red Hat Enterprise Linux 7
Managing Temporary Files	Using "tmpwatch"	RHEL 7 uses systemd-tmpfiles (more structured, and configurable, method to manage tmp files and directories).

References: All the information is taken from internet and RHEL site 

Please comments and suggestions are always welcome.

Keywords: difference between 6.x and 7.x, RHEL 6.x, RHEL 7.x, RHEL Features, RHEL.6.x Features, RHEL 7.x Features