Q. How do I convert images from a shell prompt? For example convert an image in the JPEG format to PNG or vise versa?

A. You need to use the convert command which is a member of the ImageMagick suite of tools. Use it to convert between image formats as well as
=> Resize an image
=> Blur an image
=> Crop an image
=> Despeckle an image
=> Dither an image
=> Draw on an image
=> Flip an image
=> Join an image
=> Re-sample, and much more.

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Q. How can I set the system date and time from the command prompt (bash shell)? I don’t have GUI installed and I am login over ssh session.

A. Use date command to display the current date and time or set the system date / time over ssh session.

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Q. I am trying to unmount remotely hosted Linux server. I have CD mounted and when ever I type command umount /cdrom or umount /dev/cdrom I get an error that read as follows:
unmount: /cdrom device is busy

How do I solve this problem?

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Q. How do I replace a string with another string in all files? For example, ~/foo directory has 100s of text file and I’d like to find out xyz string and replace with abc. I’d like to use sed or any other tool to replace all occurrence of the word.

A.sed command is designed for this kind of work i.e. replace strings.

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Q. I run a Linux webserver and down time is not an option for me. Now I I made some changes to my /etc/inittab file. How do I make those changes effective without rebooting my Debian Linux server?

A. The inittab file describes which processes are started at bootup and during normal operation (e.g. /etc/init.d/boot, /etc/init.d/rc, gettys…). Init distinguishes multiple runlevels, each of which can have its own set of processes that are started. Valid runlevels are 0-6 plus A, B, and C for ondemand entries.

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