RHEL6 Vs RHEL7

Release Name

RHEL 6 – Santiago
RHEL 7 – Maipo

Gnome Version

RHEL 6 – GNOME 2
RHEL 7 – GNOME 3.8

KDE Version

RHEL 6 – KDE 4.1
RHEL 7 – KDE 4.6

NFS Version

RHEL 6 – NFS 4
RHEL 7 – NFS 4.1. NFS V2 is deprecated in RHEL 7

Samba Version

RHEL 6 – SMB 3.6
RHEL 7 – SMB 4.4

OS BOOT TIME

RHEL6: 40 sec

RHEL7: 20 sec

MAXIMUM SIZE OF SINGLE PARTITION

RHEL6: 50TB(EXT4)

RHEL7: 500TB(XFS)

BOOT LOADER

RHEL6:  /boot/grub/grub.conf

RHEL7: /boot/grupb2/grub.cfg

PROCESSOR ARCHITECTURE

RHEL6: It support 32bit & 64bit both

RHEL7: It only support 64bit

HOW TO FORMAT OR ASSIGN A FILE SYSTEM IN

RHEL6:      #mkfs.ext4   /dev/hda4

RHEL7:       #mkfs.xfs   /dev/hda3

HOW TO REPAIR A FILE SYSTEM IN

RHEL6:  #fsck -y /dev/hda3

RHEL7:  #xfs_repair /dev/hda3

COMMAND TO MANAGE NETWORK IN RHEL6 AND RHEL7

RHEL6:  #setup

RHEL7:  #nmtui

HOSTNAME CONFIGURATION FILE

RHEL6:    /etc/sysconfig/network

RHEL7:    /etc/hostname

DEFAULT ISO IMAGE MOUNT PATH

RHEL6: /media

RHEL7: /run/media/root

FILE SYSTEM CHECK

RHEL6:   e2fsck

RHEL7:   xfs_repair

RESIZE A FILE SYSTEM

RHEL6:   #resize2fs -p /dev/vg00/lv1

RHEL7:    #xfs_growfs  /dev/vg00/lv1

Run Levels

RHEL 6 – runlevel 0 – Power Off
runlevel 1 – Single User Mode
runlevel 2 – Multi User without Networking
runlevel 3 – Multi User CLI
runlevel 4 – Not USed
runlevel 5 – GUI Mode
runlevel 6 – Restart

RHEL 7 – There is no run levels in RHEL 7. Run levels are called as targets
Poweroff.target
rescue.target
multi-user.target
graphical.target
reboot.target

UID Information

RHEL 6 – Normal User UID will start from 500 to 65534
System Users UID will start from 1 to 499

RHEL 7 – Normal User UID start from 1000 – 65534
System Users UID will start from 1 to 999Because Services are increased compare to RHEL 6

By Pass Root Password Prompt

RHEL 6 – append 1 or s or init=/bin/bash to Kernel command line
RHEL 7 – Append rd.break or init=/bin/bash to kernel command line

Rebooting and Poweroff

RHEL 6 – poweroff – init 0
reboot – init 6

RHEL 7 – systemctl poweroff
systemctl reboot

YUM Commands

RHEL 6 -yum groupinstall
yum groupinfo

RHEL 7 – yum group install
yum group info

Default Inode Size

RHEL 6 – 256 bytes

[root@local ~]# tune2fs -l /dev/sda1|grep -i ‘inode size’

Inode size: 128

RHEL 7 – 512 bytes

[root@managed1 ]# xfs_info /dev/sda1|grep isize

meta-data=/dev/sda1 isize=512 agcount=4, agsize=65536 blks

Resizing an Lvm

RHEL 6 – EXT family of file systems could be resized if built on a logical volume as a block device.

RHEL 7 – As with XFS file system, resize is not possible.

TUNE A FILE SYSTEM

RHEL6: tune2fs

RHEL7: xfs_admin

IPTABLES AND FIREWALL

RHEL6: iptables

RHEL7: firewalld

IPtables

To see firewall status in RHEL7

#firewall-cmd   –state

To see Firewall status in RHEL6

#service iptables status

To stop firewall in RHEL7

#systemctl stop firewalld.service

To stop firewall in RHEL6

#service iptables stop

COMMUNICATION BETWEEN TCP AND UDP IN BACK END

RHEL6: netcat

RHEL7: ncat

INTERFACE NAME

RHEL6: eth0

RHEL7: ens198(N)

COMBINING NIC

RHEL6: Network Bonding

RHEL7: Team Driver

NSF Server Version

RHEL6:  NFSv2

RHEL7:  NFSV4

DATABASE USED

RHEL6: Mysql

RHEL7: mariaDB

RHEL7 also support Mysql

MANAGING SERVICES

RHEL6:

#service sshd restart

#chkconfig sshd on

RHEL7:

#systemctl restart sshd

#systemctl enable shhd

File System.

RHEL6 default file system is ext4

xfs is RHEL7 default file system.

Kernel Version

RHEL6 default kernel version is 2.6 while RHEL7 is 3.10

UID Allocation

In RHEL6 default UID assigned to users would start from 500 while in RHEL7 it’s starting from 1000.
But this can be changed if required by editing /etc/login.defs file.

Maximum supported File Size.

In RHEL6 maximum file size of an individual file can be up to 16TB while in RHEL7 it can be up to 500TB which is very large in comparison to RHEL6.

Maximum Supported File System Size.

In RHEL6 maximum file system size=16TB (for 64bit Machine) and 8TB (for 32 bit machine). While in RHEL7 maximum file system size is 500TB.

Also keep in mind that RHEL does not support XFS on 32-bit machines.

Change in file system structure.

In rhel6 /bin,/sbin,/lib and /lib64 are usually under /

In rhel7, now /bin,/sbin,/lib and /lib64 are nested under /usr.

The /tmp directory can now be used as a temporary file storage system (tmpfs)

Space Required to Installing RHEL7?

Now if you want to install RHEL7 in your machine, RedHat recommends minimum 5 GB of disk space to install this release of RHEL series for all supported architectures.

.Hostname lookup and setup 

In rhel5 and rhel6 versions, we can edit file /etc/sysconfig/network to set hostname but in rhel7 we can directly change the hostname using below commands.

hostnamectl

nmtui

nmcli

Example:

in RHEL6              #hostname

in RHEL7              #hostnamectl  status   and #hostname

Few More notable changes in RHEL 7.

Netstat and ifconfig commands also disappeared from RHEL7 but it can be used by installing net-tools.

The move from sysvinit to systemd is one of most important change that has been made and which is a matter of concerned.

Command tail -n is replaced by journalctl -n

Command tail -f is replaced by journalctl -f

For displaying kernel messages instead of dmesg now in RHEL7 we use journalctl –k

ext2 vs ext3 vs ext4 vs xfs file system differences

Ext2

•             Ext2 stands for second extended file system.

•             It was introduced in 1993. Developed by Rémy Card.

•             This was developed to overcome the limitation of the original ext file system.

•             Ext2 does not have journaling feature.

•             On flash drives, usb drives, ext2 is recommended, as it doesn’t need to do the over head of 

               journaling.

•             Maximum individual file size can be from 16 GB to 2 TB

•             Overall ext2 file system size can be from 2 TB to 32 TB

How to create an ext2 filesystem

# mke2fs /dev/sda1

Ext3

•             Ext3 stands for third extended file system.

•             It was introduced in 2001. Developed by Stephen Tweedie.

•             Starting from Linux Kernel 2.4.15 ext3 was available.

•             The main benefit of ext3 is that it allows journaling.

•             Journaling has a dedicated area in the file system, where all the changes are tracked. When

               the system crashes, the possibility of file system corruption is less because of journaling.

•             Maximum individual file size can be from 16 GB to 2 TB

•             Overall ext3 file system size can be from 2 TB to 32 TB

•             There are three types of journaling available in ext3 file system.

o             Journal – Metadata and content are saved in the journal.

o             Ordered – Only metadata is saved in the journal. Metadata are journaled only after writing

               the content to disk. This is the default.

o             Writeback – Only metadata is saved in the journal. Metadata might be journaled either

                before or after the content is written to the disk.

•             You can convert a ext2 file system to ext3 file system directly (without backup/restore).

How to create ext3 file system :-

# mkfs.ext3 /dev/sda1

(or)

# mke2fs –j /dev/sda1

( -j for adding journaling capability )

How to  convert  ext2 to ext3 :-

# umount /dev/sda2

# tune2fs -j /dev/sda2

# mount /dev/sda2  /var

 Ext4     

•             Ext4 stands for fourth extended file system.

•             It was introduced in 2008.

•             Starting from Linux Kernel 2.6.19 ext4 was available.

•             Supports huge individual file size and overall file system size.

•             Maximum individual file size can be from 16 GB to 16 TB

•             Overall maximum ext4 file system size is 1 EB (exabyte). 1 EB = 1024 PB (petabyte). 

              1 PB = 1024 TB (terabyte).

•             Directory can contain a maximum of 64,000 subdirectories (as opposed to 32,000 in ext3)

•             You can also mount an existing ext3 fs as ext4 fs (without having to upgrade it).

•             Several other new features are introduced in ext4: multiblock allocation, delayed allocation,

               journal checksum. fast fsck, etc. All you need to know is that these new features have

               improved the performance and reliability of the filesystem when compared to ext3.

•             In ext4, you also have the option of turning the journaling feature “off”.

Creating ext4 file system :-

# mkfs.ext4 /dev/sda1

(or)

# mke2fs -t ext4 /dev/sda1

Converting ext3 to ext4

( Warning :- Never try this live or production servers )

# umount /dev/sda2

# tune2fs -O extents,uninit_bg,dir_index  /dev/sda2

# e2fsck -pf /dev/sda2

# mount /dev/sda2 /var

Find your servers filesystem type

We can find the filesystem type used in our servers using any one of the following commands

# mount

/dev/sda3 on / type ext3 (rw)

proc on /proc type proc (rw)

/dev/sda1 on /boot type ext3 (rw)

tmpfs on /dev/shm type tmpfs (rw)

# file -sL /dev/sda1

/dev/sda1: Linux rev 1.0 ext3 filesystem data (needs journal recovery)

# df -T | awk ‘{print $1,$2,$7}’ | grep “^/dev”

/dev/sda3 ext3 /

/dev/sda1 ext3 /boot

XFS

XFS is a high-performance file system which was designed by SGI for their IRIX platform. 

Since XFS was ported to the Linux kernel in 2001, XFS has remained a preferred choice for many enterprise systems especially with massive amount of data.

XFS is  a high performance filesystem,due to its high performance, architectural scalability and robustness. For example, RHEL/CentOS 7 and Oracle Linux have adopted XFS as their default file system, and SUSE/openSUSE have long been an avid supporter of XFS.

XFS has a number of unique features that make it stand out among the file system crowd, such as scalable/parallel I/O, journaling for metadata operations, online de-fragmentation, suspend/resume I/O, delayed allocation for performance, etc.

If you want to create and mount an XFS file system on your Linux platform, here is how to do it.

XFS is packed full of cool features like 

1. guaranteed rate I/O 
2. online resizing
3. built-in quota enforcement
4. it can theoretically support filesystems up to 8 exabytes in size. 

It’s been used on Linux since about 2001, and is available as an install option on many popular Linux distributions. With variable block sizes, you can tune your system like a sliding scale to tweak for space efficiency or read performance. Best for extremely large file systems, large files, and lots of files Journaled (an asymmetric parallel cluster file system version is also available) POSIX extended access controls The XFS file system is Open Source and included in major Linux distributions. It originated from SGI (Irix) and was designed specifically for large files and large volume scalability. Video and multi-media files are best handled by this file system. Scaling to petabyte volumes, it also handles great deals of data. It is one of the few filesystems on Linux which supports Data Migration (SGI contributed the Hierarchical Storage Management interfaces into the Linux Kernel a number of years ago). SGI also offers a closed source cluster parallel version of XFS called cXFS which like cVxFS is an asymmetrical model. It has the unique feature, however, that it’s slave nodes can run on Unix, Linux and Windows, making it a cross platform file system. Its master node must run on SGI hardware. Recommended Use: If you really like to tweak your system to meet your needs, XFS is a great way to go.

The XFS file system is an extension of the extent file system .XFS is a high performance 64 bit journaling file system .Support of XFS was merged into the linux kernel in around 2002 and In 2009 Red Hat Enterprise Linux version 5.4 usage of XFS file system .

Default file system in RHEL7 is XFS

XFS supports maximum file system size of 8 exbibytes for 64 bit file system .Some comparison of XFS file system is XFS file system cannot be shrunk and poor performance with deletions of large numbers of files.

32-bit system 64-bit system

File size: 16 Terabytes 16 Exabytes

File system: 16 Terabytes 18 Exabytes

How to change the default run level in RHEL7?

In earlier version of RHEL, we used to change the runlevels in /etc/inittab file.

But inittab is no longer used when using systemd. systemd uses ‘targets’ instead of runlevels.

By default there are 2 main targets

graphical.target à Runlevel 5 having GUI

 multi-user.targetàRunlevel 3 text based

To view current default runlevel/target

# systemctl get-default

To set a different target

#systemctl set-default TARGET.target

Ex: systemctl set-default graphical.target

Verification:

# systemctl get-default

graphical.target

Now reboot the machine to check whether the machine is booting up into graphical mode.

Alternate method to change the runlevel

You may be noticed the similar output when the systemctl set-default multi-user.target command is issued. What the command done is nothing but making a symbolic link of runlevel targets to the default target file.

rm '/etc/systemd/system/default.target'

ln -s '/usr/lib/systemd/system/multi-user.target' '/etc/systemd/system/default.target'

Check the current level.

# systemctl get-default

multi-user.target

Before making the symbolic link, let’s list out the files in the systemd directory.

# ls /lib/systemd/system/runlevel*target -l

lrwxrwxrwx. 1 root root 15 Aug  3 13:44 /lib/systemd/system/runlevel0.target -> poweroff.target

lrwxrwxrwx. 1 root root 13 Aug  3 13:44 /lib/systemd/system/runlevel1.target -> rescue.target

lrwxrwxrwx. 1 root root 17 Aug  3 13:44 /lib/systemd/system/runlevel2.target -> multi-user.target

lrwxrwxrwx. 1 root root 17 Aug  3 13:44 /lib/systemd/system/runlevel3.target -> multi-user.target

lrwxrwxrwx. 1 root root 17 Aug  3 13:44 /lib/systemd/system/runlevel4.target -> multi-user.target

lrwxrwxrwx. 1 root root 16 Aug  3 13:44 /lib/systemd/system/runlevel5.target -> graphical.target

lrwxrwxrwx. 1 root root 13 Aug  3 13:44 /lib/systemd/system/runlevel6.target -> reboot.target

As per the previous step, current default run level 3. 

Issue the following command to make a symbolic link of runlevel5.target to default.target file.

# ln -sf /lib/systemd/system/runlevel5.target /etc/systemd/system/default.target

or

# ln -sf /lib/systemd/system/graphical.target /etc/systemd/system/default.target

Again check the current level.

# systemctl get-default

runlevel5.target

Now the default runlevel is 5 (graphical mode), reboot the server and check it out.

# reboot