Troubleshooting

  • Connecting two computers with Ethernet LAN cable

    Quite often, we wish to connect two computers back to back using an Ethernet LAN cable. It may be because we wish to transfer files between the two computers or because one of these has the Internet access and we wish to have one more access point to the Net. The step by step instructions ...

  • Nginx 502 bad gateway error after switching off the mobile theme

    The WPtouch plugin gives a WordPress website the capability to be displayed on mobile devices using a suitable theme. At the end of the web page, there is a toggle button to switch off the mobile theme and use the default desktop theme. That is, a user can toggle ...

  • Nginx installation and configuration

    The configuration is nginx HTTP server, PHP FastCGI Process Manager (PHP-FPM), and the Alternative PHP Cache (APC).

    Installation

    The first step is to download the nginx software from the Nginx website. If using the Ubuntu distribution, following are the steps,

    (i) Download the nginx signing keys from the ...

  • Formatting the man command output for printing

    1. Limiting the width of Linux man command output

    Quite often, we need to print the output of the Linux man command. One way is to redirect the man command output to a file, open the file in LibreOffice Writer and export to PDF. The PDF can, later, be ...

  • Starting a network server after communication interface is up

    If you have a program that communicates over the network interface, say, eth0 and you wish to start the program automatically after the system startup, you need to ensure that the program starts after the interface eth0 is up. For Linux systems using the Upstart process ...

  • md5sum: no properly formatted MD5 checksum lines found

    md5sum is used for printing or checking a file's 128-bit MD5 checksum. One can download a file on the Internet and also download its checksum. The md5sum command can, then, be used to verify whether the file has been correctly received. Also, while providing a link for download for a file on a web page, ...

  • Remote Display With the X – Window System

    X – Window system is a network-transparent window system. X11 server is the display server that manages the output on the bit-mapped display hardware. An application (or client) does the work and sends requests to the X11 server, or simply, the X server for display. The client application and the X server are usually located ...

  • JRobin: Not able to save graph as a PNG file

    Error:

    Not able to save graph as a PNG file.  
    Compilation error: cannot find symbol  
     symbol  : method saveAsPNG(java.lang.String,int,int)  
    

    Solution:

    saveAsPNG does not seem to be there in JRobin anymore. Use the RrdGraph.render (java.awt.Graphics g) method. For example,

    
    // Create a buffered image in which the ...
  • Watermarking images using GIMP

    After having created images with hard work, you wish to protect your copyright on the images. Watermarking the images is an excellent method prevent any commercial misuse of images. And it can be done easily using the wonderful open source image editing software, Gimp.

    We will look at the process of watermarking images with an example. ...

  • Making a logo using GIMP

    If you are looking for Xtns menu of toolbox, don't, as, starting with Gimp version 2.6 the Gimp developers have removed the toolbox menu bar and merged it with the image window menubar. To make a logo, go to the image window menu bar. Select File -> Create -> Logos. Under Logos, you may ...

  • kernel panic – not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

    A new Linux kernel was built using the commands, make gconfig, make, sudo make install and sudo make modules_install. After building a new Linux kernel and booting from it, the boot process halts with the following message:

    kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
    



    A ...

  • Gtk-WARNING **: cannot open display:

    While running a GTK+ based C program under Cygwin, the following runtime error is observed,

    Gtk-WARNING **: cannot open display:
    
    

    SOLUTION

    1. Make sure that Cygwin/XServer is installed and is running. If it is not installed, download the relevant packages from Cygwin.

    2. Make sure that environment variable DISPLAY is defined ...
  • cygwin1.dll not found

    A C program was compiled under Cygwin and run directly under Windows. The following runtime error was observed,

    cygwin1.dll not found
    
    

    SOLUTION

    Make sure that the environment variable, PATH, has the directory C:\gygwin\bin which contains the dll, cygwin1.dll.

    On Windows Vista, this can be ...

  • Mounting Windows partitions under Linux

    Multi-boot systems with Linux and Windows are quite common. With the following steps, it is easy to access Windows partitions under Linux.

    1. Examine the disk partitions. For example,

    sudo fdisk -l
    

    gives the output,

    Disk /dev/sda: 160.0 GB, 160041885696 bytes  
    255 heads, 63 sectors/track, 19457 cylinders  
    Units = cylinders of ...