How to configure Linux to Support Multicast IP

Most Linux systems have multicast IP capability turned off by default. In order to use multicast sockets on my Linux system, I had to reconfigure and build my kernel, and then run the following command as root after re-booting:

How to convert images between formats

Use convert to convert the file format of an image. Give the name of the file to convert as the first argument, and the destination file as the second argument. When you convert a file, the original is not altered.

How to verify any e-mail account using shell

Use vrfy to determine whether or not a given email address works. This is useful when you are unsure whether or not you have the right email address for someone. If the address works, vrfy outputs a message indicating that the recipient exists; if the address is not valid, vrfy outputs a message saying that the user is unknown.

How to save files from URLs using shell

To download a single file from the Web, give the URL of the file as an argument to wget.

For example, to download to a file, type: $ wget RET

How to archive an Entire Web Site

To archive a single Web site, use the `−m' ("mirror") option, which saves files with the exact timestamp of the original, if possible, and sets the "recursive retrieval" option to download everything. To specify the number of retries to use when an error occurs in retrieval, use the `−t' option with a numeric argument−−−`−t3' is usually good for safely retrieving across the net; use `−t0' to specify an infinite number of retries, good for when a network connection is really bad but you really want to archive something, regardless of how long it takes. Finally, use the `−o' with a file name as an argument to write a progress log to the file−−examining it can be useful in the event that something goes wrong during the archiving; once the archival process is complete and you've determined that it was successful, you can delete the log file.

How to use dig

When you know the name of a particular host, and you want to find the IP address that corresponds to it, ping the host in question; this will output the IP address of the host in parenthesis.

Removing a File with a Strange Name

Files with strange characters in their names (like spaces, control characters, beginning hyphens, and so on) pose a problem when you want to remove them. There are a few solutions to this problem.

Write−Protecting a File

If you revoke users' write permissions for a file, they can no longer write to or remove the file. This effectively "write−protects" a file, preventing accidental changes to it. A write−protected file is sometimes called a "read only" file.

How to find files in a directory by modification Time

To find files last modified during a specified time, use find with the `−mtime' or `−mmin' options; the argument you give with `−mtime' specifies the number of 24−hour periods, and with `−mmin' it specifies the number of minutes.

How to find differences between files

Use diff to compare two files and output a difference report (sometimes called a "diff") containing the text that differs between two files. The difference report is formatted so that other tools can use it to make a file identical to the one it was compared with. To compare two files and output a difference report, give their names as arguments to diff.

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