Monthly Archives: August 2017

Get your Linux ISO download from these URLs

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List of all Linux ISO download links. The latest and old releases of various Linux distro can be downloaded using links listed on this page.

Linux download links

Many times I come across questions from people or readers that where I can download RHEL iso? Where to download Ubuntu Linux? etc. Actually these download links are very easy to get from Google but still I thought of publishing them all in one place.

In this post, I will list all possible Linux download websites. Please note that all Linux distro’s server copy is taken into consideration for choosing download links.

  1. Red Hat Enterprise Linux RHEL latest release download link.  Old releases download link. You have to create a developer account here to get your ISO copy.
  2. CentOS Linux latest release download link. Old releases download link. No signup needed.
  3. Fedora Linux download link. No signup needed.
  4. Debian Linux download link. There are country wise FTP mirrors listed. Choose your nearest one and download it.
  5. Ubuntu Linux Latest release download link. Old releases download link
  6. Arch Linux download link. Country-wise HTTP mirror list.
  7. Kali Linux latest release download link. Old releases download link
  8. Linux mint latest release download link. Old releases download link
  9. OpenSUSE Linux latest release download link
  10. SUSE Linux 60 days trial download link
  11. Open Mandriva Linux download link
  12. Kubuntu Linux download link
  13. Bodhi Linux download link
  14. Gentoo Linux download link

The list will go on since Linux is open source and there are many distros floating around the internet! Report broken links and any additions in the comments below.

7 new features in RHEL7!

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Listing new features in RHEL7. These 7 new features making RHEL7 stand out from its predecessor. 

New features in RHEL7

Its been a while RHEL7 is launched and nicely accommodated in Linux world by now. What’s new in RHEL7? What is the difference between RHEL7 and its precedence versions? these kinds of questions are flowing through interviews these days. So thought of jotting them down. In this post I will quickly walk through some new key features launched in RHEL7 by Red Hat.

What’s new in RHEL7?

RHEL7 officially released in June 2014 with codename Maipo. It took time for the market to absorb this new release since there are many new features launched in this release. Red Hat launched many new ways, commands to do traditional stuff. We are going to see them now –

  1. The default file system is XFS. RHEL6 was launched with EXT4 as the default file system. XFS is a highly scalable, high-performance file system. XFS supports metadata journaling, which helps in quicker crash recovery. This means file system checks will take very little time. The XFS file system can be defragmented and extended while mounted. This makes it more admin friendly in a production environment since it avoids downtime of file systems for activities. Supports only 64 bit systems.
  2. Introduction of systemctl. A new way to manage services on RHEL7 is systemctl. Older service and chkconfig command is being replaced with systemctl.
  3. Run levels being called as targets. In RHEL7 run levels are called targets. Default target (run-level) is defined in /etc/systemd/system/default.target. 
  4. Fast boot. RHEL7 boots faster than its predecessors. This is achieved by simultaneously starting services that are not dependent on each other. In older versions, services used to start one after another. So if one service stuck or delays to start it subsequently delays the following process and boot time. This hurdle is removed in RHEL7 allowing it to boot much faster.
  5. New system service manager: systemd. The former init process is no more PID 1 or first process. Systemd is introduced which controls standard base init scripts.
  6. Bigger filesystem limits. RHEL7 now supports filesystem size up to 500TB. This limit is also the same for an individual file. This is due to the XFS file system on a 64-bit machine. RHEL6 supports the 16TB filesystem.
  7. New firewall identity. Former firewall iptables now replaces by firewalld (Firewall Dynamic). iptables still exist in the system and you can disable firewalld and use iptables.

These are key differences in the new RHEL7 release. apart from this there are many new things added in RHEL7. The whole list is compiled by Red Hat here.

Let us know your suggestions/feedback in comments section below!

How to unmount NFS when the server is offline

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Learn how to unmount NFS when the server is gone. Dead NFS mounts can be un-mounted using forceful and lazy umount command.

Unmount NFS share when server is gone

This article will help you to un-mount NFS share from the client when the NFS server is gone or offline or un-available or decommissioned. We have seen how to configure the NFS server and how to handle NFS stale file error. But what if your NFS server is gone and its shares are still mounted on clients. Normally, before shutting down the NFS server, all clients should be notified and advised to unmount NFS shares they are using from this server.

But, in case if any of the clients have still NFS mounted when the server goes down, then the client should forcefully un-mount it. Normal mount operation won’t be effective in such cases. When the NFS server is down, you observe below things on the client who has NFS share still mounted.

  1. df command hangs since it tries to fetch NFS information but the NFS server is not responding.
  2. Tools, utilities who use/check mount point information like Ignite backup shows below error. 
    NFS server xyz not responding still trying
  3. fuser command hangs when running for the NFS mount point.
  4. umount (normal) command fails with the below error. 
    root@kerneltalks # umount /data nfs umount: nfs_unmount: /data: is busy umount: return error 1.

In this case, you need to use forceful (-f switch) and lazy umount (-l switch) to un-mount this dead NFS mount point. Lazy un-mount detach the said mount point from file system tree and cleans its all references once it’s not busy anymore.

Lazy un-mount is available in most Linux distributions. If not, you should be fine with only forceful un-mount too. In HPUX lazy un-mount is not available.

root@kerneltalks # umount -f -l /data

Conclusion

You can identify dead NFS share by df, fuser commands that appear to hang, failing to umount command. Such a dead NFS mount point can be un-mounted using forceful and lazy umount command.

How to replay Linux session recorded by the script command

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Learn how to replay the Linux session recorded by script command. Visual Linux session recording along with timing information plays past session recording in real-time.

Replay Linux session like video!

In our last article we learned how to record Linux sessions using the ‘script’ command. In this article we will walk through steps to replay recorded sessions by script command. Normally, script command saves recording in the plain text log file which can be viewed using cat, more, less, or vi commands. That would be only plain text having commands and their outputs in the order you executed them while recording.

If you want to view your recorded output as it is being played on the terminal you can do it using scriptreplay command. It will play your output just as you are typing it on the terminal! scriptreplay needs time logs as well to play recorded sessions. This time logs can be generated using –timing switch with the script command. Let’s walk through these steps.

How to record Linux session with timing

We will use script command with --timing switch followed by filename in which all timing logs will be saved.

[root@kerneltalks ~]#  script --timing=time.log capture.txt
Script started, file is capture.txt
[root@kerneltalks ~]# date
Thu Jul 27 02:42:46 EDT 2017
[root@kerneltalks ~]# hostname
kerneltalks
[root@kerneltalks ~]# echo "I love kerneltalks"
I love kerneltalks
[root@kerneltalks ~]# exit
exit
Script done, file is capture.txt

here we are saving timing information in time.log file and session recording in capture.txt file. Both are plain text files and can be viewed. If you look at time.log file :

[root@kerneltalks ~]# cat time.log
0.001666 53
0.009220 1
3.980549 1
0.103633 1
0.191978 1
0.096629 2
0.127128 75
0.000920 1
1.671676 1
0.143421 1
0.080831 1
0.152510 1
----- output trimmed----

It has two columns of data in it. The first column denotes the number of seconds elapsed after the last display action. The second column is the number of characters printed on the screen.

That’s it. You have recorded your Linux session along with timing logs. This recording (capture.txt) can be replayed using scriptreplay command since its timing information is available.

How to replay recorded Linux session

Now both logs timing and recording need to feed scriptreplay command to let the show begin! The format and switch would be the same. Command used to replay session will be :

# scriptreplay --timing=time.log capture.txt

To see it in action, I captured it in the GIF file below. See how to actually replay as if the user is typing in the terminal as it was at the time of recording!

‘scriptreplay’ command in action

It replays exactly with the same time difference between two commands as you did at the time of recording! It’s like watching what the user has done in his session in real-time. It’s more of a visual record of Linux session while script was textual records.