The I/O scheduler policy has changed with Red Hat Enterprise Linux 7.
The default I/O Scheduler is now CFQ for SATA drives and Deadline for everything else.
Indeed, for faster storage than SATA drives, Deadline outperforms CFQ, giving a performance increase without any special tuning.
Additional information and instructions are available in the I/O scheduler tutorial.
One year ago I decided to start this website.
One of the reasons explaining this move was to see how it was difficult to complete some tasks like LDAP client configuration without almost any tutorial to set up the server side.
Now that Red Hat is increasing the level of the RHCE exam, nothing has really changed. There is still a need for LDAP/Kerberos/DNS server side tutorials to test the client side objectives.
Today, I sincerely hope this website is useful to you. If you have learned some tips, I can tell you, I have learned a lot! One year ago I didn’t know what a powerful tool was WordPress and I never ran a website before.
What a wonderful adventure!
The Red Hat certification team recently made some adjustments to the RHCSA & RHCE exams objectives for RHEL 7.
Concerning the RHCSA exam, VNC and LUKS related tasks have been removed, when firewall settings can now be set up through iptables or firewalld, which is very sensible. The client LDAP configuration, although no longer directly specified, seems to remain an objective through the client configuration to an authentication service.
This appears to be a slight adjustment with very limited consequences.
Concerning the RHCE exam, access to Samba shares through Kerberos authentication has been added when Rsyslog client & server configurations have been removed.
Two easy tasks have been replaced with a complicated one, emphasizing again the weight of Kerberos.
A RHCE 7 candidate will definitely need serious Kerberos skills! At least, it’s what Red Hat people want.
Two days ago, the Linux Foundation announced a new certification program.
It consists in two exams:
Both exams are performance-based exam in English lasting 2 hours focusing on system administration and costing $300 ($50 until 24/8).
Candidates can choose between 3 Linux distributions (CentOS 6.4, OpenSUSE 13.1 and Ubuntu 14.04) before the beginning of the exam.
Compared to the RHCSA6 exam, the new LFCS exam on Centos 6.4 requires additional sudo, backup/restore and Raid configuration skills.
Similarly, compared to the RHCE6 exam, the new LFCE exam on CentOS 6.4 requires additional Apache SSL, Squid and IMAP/IMAPS configuration skills.
Time will tell us if this new Linux Foundation certification program can get some success.
Some applications writing files in the /tmp directory can see huge improvements when memory is used instead of disk.
By default in RHEL 7 / CentOS 7, the /tmp directory resides in the logical volume/physical partition associated with /:
# df -k /tmp
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/mapper/rhel-root 3030800 1069380 1787752 38% /
Here, another way to check the configuration:
# systemctl is-enabled tmp.mount
To change this behavior and put the /tmp directory into memory, type:
# systemctl enable tmp.mount
Now, if you check the new configuration, this is what you get:
# df -k /tmp
Filesystem 1K-blocks Used Available Use% Mounted on
tmpfs 508988 8 508980 1% /tmp
Remember not to write big files due to the limited space and, obviously, don’t expect persistence across reboots.
If you don’t know the kpartx command, you miss something!
If you regularly play with virtual machines under KVM, you know that sometimes things go wrong.
A change in the /etc/fstab file or in the ssh configuration and you are in trouble, you can no longer access your virtual machine because you hadn’t set any virtual console: you need to reinstall it and it’s not fun!
But there is a solution! I call it emergency procedure.
This solution consists in stopping your virtual machine with the destroy command, then map your virtual machine image file in your physical host environment with the kpartx command. Mount the /boot partition and edit your /boot/grub2/grub.cfg file, adding the console=ttyS0 string at the end of every kernel boot line.
Finally, unmount the /boot partition, unmap your virtual machine image and reboot your virtual machine: from now on, you’ve got your virtual console!
This tip works at least for RHEL 6/CentOS 6 and RHEL 7/CentOS 7.
To get all the details, go to the RHEL 7 virtual console page.
With Systemd, the Init scripts are not there any more. Consequently, the execution of tasks at boot time had to change.
Hopefully, a nice solution has been found: it uses the good old rc.local file.
Now, to execute tasks at boot time, you put them into the /etc/rc.d/rc.local file.
Then, you change the execution permissions on this file:
# chmod u+x /etc/rc.d/rc.local
Besides allowing executions of tasks, this simple operation activates the new rc-local Systemd service for all the further boots (this is like systemctl enable in Systemd language).
Finally, you can start the rc-local service and, this way, test the execution of the rc.local file:
# systemctl start rc-local
SSD optimization is a good example of such a rc-local service.
Just a reminder for RHCEv5: you’ve got still 29 days to get recertified by passing the RHCEv6 only (a 50% discount is available in some countries).
Today, CentOS 7 has just been released.
The distribution can now be downloaded from the CentOS website.
The Release Notes explain what kind of images are available:
- the DVD images contain most of the packages but not all,
- the Live media images are also stored on DVD and allow you to decide to install the distribution or not with a reduced number of packages,
- the Livecd image, stored on a CD, is a basic distribution,
- the Everything image contains all the available packages.
In addition, the CentOS 7 FAQ gives you some tips:
- How to activate your Ethernet network interface during the installation,
- How to keep the old network interface names,
- How to disable IPv6.
This is a good news for those who want to start to learn RHEL 7 but can’t afford to pay the fee.
Yesterday, there was a live chat organized by Red Hat on Twitter.
The subjects were RHEL 7 training and certifications.
Here is a retranscription:
- RHCSAv6 & RHCEv6 exams are available until December, the 19th but availability varies by location.
- According to location, RHCSAv6 & RHCEv6 can still be taken in exam centers or only in kiosk/onsite.
- A candidate with a current or future RHCSAv6 can become RHCEv7 by passing the RHCEv7 exam only.
- Red Hat recommends taking the RHCE Certification Lab, available as classroom, virtual training, & online, before taking the RHCEv7.
- According to location, a RHCEv5 can get a 50% discount to take both RHCSAv6 et RHCEv6.
- The RHCEv7 changes (4 hours instead of 2, more topics, etc) have been made based on input and guidance of Red Hat Certified Professionals.
- All kiosk exam environments are entirely local (no latency) and keyboards can be remapped if a localized keyboard is not already available.
- Other courses will be updated to RHEL 7 before the end of this year.
- It is still possible to (re)download a certificate/transcript (“Red Hat hereby certifies…”) for a RHCEv5.
- Courses on RHEL 7 have already started in North America.
- UK kiosk is available in Farnborough and a new London location is looked for.
- The opening of a kiosk in Poland is under consideration.
- RHEL 7 training material should be available in French within the Summer.