Friday, February 2, 2018

A few advanced differences between RHEL7.x & RHEL6.x



Extracting initramfs image :--
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Using "skipcpio" command in RHEL7.x, otherwise, we use "gunzip" in earlier RHEL versions. So, the command to extract initramfs image file in RHEL7.x is " /usr/lib/dracut/skipcpio /boot/initramfs-$(uname -r).img | gunzip -c | cpio -id ". In earlier versions, we could do this by using the command gunzip "gunzip -c /boot/initramfs-$(uname -r).img | cpio -i -d ".




Default Inode size :--
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In case of XFS file system this has been changed to “512 bytes” which is “256 bytes” in RHEL6.x version.


-- RHEL7.x

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

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


-- RHEL6.x

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

   Inode size: 128



iostat command :--
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Now, in RHEL7.x there is a separate r_await (read await) & w_await (write await) added along with "await" which produces total (changed in sysstat version 10). It is just "await" parameter to get total average time in milliseconds which took to complete IO requests in case of RHEL6.x version.



Network persistent device file deprecated :-
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There is no such file which maintains persistent network/device names as seen earlier versions. It has been deprecated. [https://access.redhat.com/solutions/1554703]. This was maintained by "/etc/udev/rules.d/70-persistent-network.rules" file in earlier versions.



free command :-
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Now, the “used” column of “free” command output calculates used memory size by considering “buffers/cache” value as well. So, in RHEL7.x version it is “used = total - free - buff/cache”. In earlier version it is “used = total - free”.




“tuned” installed by default:-
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The “tuned” package is installed and service is started unless disabled during installation. This has to be installed in earlier versions.




Resizing an lvm :-
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As with XFS file system, resize is not possible (https://access.redhat.com/solutions/540013). However, EXT family of file systems could be resized if built on a logical volume as a block device.



"dmesg" can print time-stamp along with data:- 
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The new "util-linux" package to which "dmesg" command belongs to can print time-stamp along with messages as storaged in /var/log/dmesg. Now, users can print human readable kernel ring buffer messages using "dmesg -T" command. Most of the user utility commands under /bin are moved to /usr/bin in RHEL7.x architecture.

In case of RHEL6.x, "dmesg" command belongs to "util-linux-ng" package and which by default doesn't record time stamp and hence, data produced doesn't state when those messages are generated.




"Btrfs" has been deprecated from RHEL7.4 on-wards:- 
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The "Btrfs" was made available as technology preview since RHEL6 and now Red Hat has decided to remove it from future release of RHEL7.4 on-wards. To view all functions/features which are deprecated in RHEL7, please visit the below link:
https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/7.4_release_notes/chap-red_hat_enterprise_linux-7.4_release_notes-deprecated_functionality

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