Category: Linux

All linux related goodies will be listed here.

VMware Player unrecoverable error: (vmx)

When I opened my VMware today, following error was displayed:

VMware Player unrecoverable error: (vmx)

Exception 0xc0000006 (disk error while paging) has occurred.

A log file is available in "C:UsersacerDocumentsVirtual MachinesRed Hat Enterprise Linux 6 64-bitvmware.log".

You can request support.

To collect data to submit to VMware technical support, run "vm-support".

We will respond on the basis of your support entitlement.

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Solution: Remove the following two files from the VMware installed directory. You can check the installed directory from Player -> Manage -> Virtual Machine Settings -> Options

  1. Red Hat Enterprise Linux 6 64-bit-93cd0331.vmem
  2. Red Hat Enterprise Linux 6 64-bit-93cd0331.vmss

[Source: http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1002347]

Unable to save changes to menu in Drupal 6

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On the menu-customize page, after

1) dragging a menu item, or

2) checking/unchecking an enable checkbox,

and clicking “Save configuration”, changes to menu were not saved in Drupal 6. Hence, I started to debug the issue at the Application level. After long head bang, I raised my hand and took some rest. Finally, I googled and found that the problem was not at the Application Level but at System Level. I came to know that while posting the form (i.e. when Save Configuration is clicked) the data sent was of large amount and the system was not able to accept since maximum input size was not defined. Following were the changes made in php.ini file.

; How many GET/POST/COOKIE input variables may be accepted
max_input_vars = 2048

After making above changes I restarted the Apache server. Thus, the problem was resolved and Save Configuration in Menu started working.

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How to take backup and restore openvz (Proxmox Virtual Environment)?

Well, I am not that sound in playing with the tools of openvz but through the assistance of professionals, I came to learn how to take backup of openvz and restore it in another proxmox virtual environment. In order to understand this tutorial, you must have a little knowledge of Linux and its basic commands. The following steps more or less clearifies the process:

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  1. Login to your proxmox via root.
  2. Check whether there is sufficient space to take backup. Use the command below to check the available space on the system:

    moon:~# df -h

    Filesystem Size Used Avail Use% Mounted on

    /dev/mapper/pve-root 95G 15G 76G 16% /

    tmpfs 16G 0 16G 0% /lib/init/rw

    udev 10M 632K 9.4M 7% /dev

    tmpfs 16G 0 16G 0% /dev/shm

    /dev/mapper/pve-data 723G 272G 452G 38% /var/lib/vz

    /dev/sda1 504M 44M 435M 10% /boot

  3. In order to list out the virtual machines type the following command:

    moon:~# vzlist

    CTID NPROC STATUS IP_ADDR HOSTNAME

    101 67 running 10.10.10.110 hindi-website.example.com

    103 206 running 10.10.10.251 maincopy.example.com

    201 92 running 10.10.10.106 engsecondary.example.com

    240 64 running 10.10.10.108 wsdb-backup.example.com

    242 78 running 10.10.10.107 hi-secondary.example.com

    410 109 running 10.10.10.104 rc.example.com

  4. Note down the CTID for which you are taking the backup. CTID is an identifier which uniquily represents the respective virtual machine.
  5. Follow the command below to take the backup of the virtual machine:

    moon:~# sudo vzdump –dumpdir /var/lib/vz/dump/ 103 –suspend –compress

The above command takes a complete backup of the virtual machine whose CTID is 103 at the location /var/lib/vz/dump/. The backup process will take approximately an hour to complete. In order to confirm the successfull backup change the directory to /var/lib/vz/dump/ and execute the command ls or dir. Two files are generated prefixed by vzdump-openvz-*.

  1. Copy the backup to another proxmox using the following command:

    moon:~# scp vzdump-openvz-103-2014_06_24-17_22_53.tgz root@10.10.10.44:/var/lib/vz/dump/

  2. In order to restore, first of all login to your proxmox via GUI.
  3. Delete the virtual machine if there is insufficient space or make some space to restore the backup.
  4. Now, Login to your proxmox using ssh or putty. Change your directory to /var/lib/vz/dump/ (location of the backup) . Execute the following command:

    earth:~# vzrestore vzdump-openvz-103-2014_06_24-17_22_53.tgz 103

The above command will restore the backup creating a complete new virtual machine. It takes approximately an hour to complete the process.

  1. Login to your proxmox via GUI. A new virtual machine will be visible. Before starting the machine modify the IP Address in order to prevent the IP conflict.
  2. If the macnine contains MySQL binded with the IP then modify the IP from the file /etc/mysql/my.conf

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How To scp, ssh and rsync without prompting for password

Following steps would help you to do scp, ssh & rsync without prompting for password:

1. On Host A where you run scp/ssh/rsync command, run the following command: 

$ ssh-keygen -t rsa

This will prompt a passphrase. After pressing enter key it’ll generate a private and a public key. Public key is saved at ~/.ssh/ by default.

2. Transfer id_rsa.pub file to Host B using scp or ftp.

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3. On Host B, login as remote user and copy the contents of id_rsa.pub to ~/.ssh/authorized_keys using the following command:

$ cat id_rsa.pub >>~/.ssh/authorized_keys
$ chmod 700 ~/.ssh/authorized_keys

4. Thats’ all, Now you can run scp, ssh and rsync command without prompting for password.

5. Note that ssh by default does not allow root to log in. This has to be explicitly enabled on Host B. This can be done by editing /etc/ssh/sshd_config and changing the option of PermitRootLoginfrom no to yes. Don’t forget to restart sshd so that it reads the modified config file. Do this only if you want to use the root login.

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MTNL Broadband Browsing Problem

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I am using MTNL Broadband for 1 and a half years. I had never faced Webpage browsing problem since then. I called MTNL Customer Care many times but they fooled me. Problem still not solved.

Then I started searching regarding the problem my own. I googled with the same title as this post. I found that huge number of MTNL Customers facing the same problem.

images

After continuous haunt for the solution I found a blog where the author introduced me about opendns. It was a new topic to me and was not that concerned. I followed the comments on that post I found some dns ips and was told that if updated on your system’s network config Browsing Problem would vanish.

Immediately, I updated my dns configuration. God damn, it worked. Thanks to the auther.

Following are the DNS IPs :

208.67.222.222,

208.67.220.220

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Starting web server: apache2(98)Address already in use: make_sock: could not bind to address 0.0.0.0:80

download

$service apache2 restart
[....] Starting web server: apache2(98)Address already in use: make_sock: could not bind to address 0.0.0.0:80
no listening sockets available, shutting down
Unable to open logs
failed!

In order to solve the above issue, type following on your console

fuser -k -n tcp 80

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Disk /dev/sdb doesn’t contain a valid partition table in Linux

drive-not-formatted

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1. Run fdisk /dev/sdb

2. Create a new partition table with ‘o’

3. Create a new partition with ‘n’

4. Let it use the default values by hitting ENTER when it asks for numbers, to take the entire available disk in this partition

5. Write the new partition table with ‘w’, which should dump you back to the prompt.

6. Finally, you should have a /dev/sdb1 to format using the following command:

  sudo mkfs.vfat -n ‘Ubuntu’ -I /dev/sdb1

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Http Error 0 in Drupal

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Http Error 0  is a very common error that occurs in Drupal. There are many reasons behind this error.

htttp-error-0

One of the way to resolve this error is to append the following line in this file : /etc/apache2/mods-available/fcgi.conf

[code]

MaxRequestLen 536870912

[/code]

Increase the number value of the MaxRequestLen until the error stops to continue.

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Load Testing on Web Servers using Apache Benchmark

ab

After working on many websites, I found one of my site getting too many traffic bringing down the site. I contacted the technical support who fixed the problem. I had never tested load on any of my site. So, I started studying load testing on web servers. This helped me to understand how many users can be handled by my website so that it can run smoothly.

I found a very light and strong linux tool called Apache Benchmark Tool that can test load on Web Servers. This can benchmark Apache, IIS and other web server with apache benchmarking tool called ab. There are also other open source tools that helps to test load on web servers.

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I executed following command on my linux terminal:

[code]

ab -c 1000 -n 1000 -t 60 -k http://ignou.ac.in

[/code]

Option -c : This option says there are 1000 concurrent users logged in on the Web Server.

Option -n : This option sends 1000 requests to the Web Server.

Option -t : This option says users will be logged in for 60 seconds.

Option -k : For Keep Alive On

I logged in to the web server and executed the following command to test the actual load.

[code]

top

[/code]

This command helped to track down the load average, CPU and Memory Utilization of the web server.

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How to redirect http requests to https on Debian Linux with Apache Web Server?

securing-apache5-590x277

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Do the following to redirect http requests to https running on Debian Linux with Apache Web Server.

File : /etc/apache2/ports.conf

[code]
NameVirtualHost *:80
Listen 80
[/code]

File : /etc/apache2/sites-availabe/default

[code]
<VirtualHost *:80>
ServerName www.example.com
Redirect / https://www.example.com/
</VirtualHost>

<VirtualHost *:443>
ServerName www.example.com
# … SSL configuration goes here
</VirtualHost>
[/code]

Restart Apache Webserver

[code]
/etc/init.d/apache2 restart
[/code]

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