How to backup your data using rsync

The most critical data to back up is data that is impossible, or very costly, to re-create. Usually this is user data that has grown over months or years of work. You can typically restore system data relatively easily by reinstalling from the original distribution media.The Linux utility rsync is a copy program designed to replicate large quantities of data. It can skip previously copied files and fragments and encrypt data transfers with ssh, making remote backups with rsync faster and more secure than they are with traditional tools like cp, cpio, or tar.




Understanding autoconf

Developing software that runs on a number of different UNIX and UNIX-like systems requires considerable effort. First, the code itself must be portable. Portable code makes few assumptions about the hardware on which it may be run or the software libraries available to it. In addition, if it’s C code, to ensure maximum portability, the code has to stick to strict ISO/ANSI C, or isolate non-standard C to as few modules as possible.




The Basics of fdisk

First, you need to know the device file of the drive to be configured. The easiest way to determine this is with the following command, which lists all connected drives—if they’re detected:

$ sudo fdisk -l




The fd Directory

The directory /proc/$pid/fd has an entry for each open file descriptor as a symbolic link to the actual file’s inode. An inode contains information about a file. Each inode has the device where the inode resides, locking information, mode and filetype of the file, links to the file, user and group ids of the owner, bytes in the file, and addresses of the file’s blocks on the disk.




Accessing Memory Using DMA

Direct Memory Access (DMA) allows internal peripherals to access memory without the processor needing to execute instructions for each transfer. There are two types of DMA; one uses the DMA controller on the motherboard and the other uses a busmaster controller on the peripheral card.




Sending e-mail from bash

To send an email message with mail, give the email addresses to which you are sending as arguments, and then type the message proper in the lines that follow; type C−d on a line by itself to signify the end of the message body, and to send the message.




Changing File Names to Lowercase

To change the uppercase letters in a file name to lowercase (or vice versa), use chcase. It takes as arguments the files whose names it should change.




Renaming Multiple Files with the Same Extension

To give a different file name extension to a group of files that share the same file name extension, use chcase with the `−x' option for specifying a Perl expression; give the patterns to match the source and target files as a quoted argument.




File Ownership

Every file belongs to both a user and a group−−usually to the user who created it and to the group the user was working in at the time (which is almost always the user's login group). File ownership determines the type of access users have to  particular files




Controlling Access to Files

Each file has permissions that specify what type of access to the file users have. There are three kinds of permissions: read, write, and execute. You need read permission for a file to read its contents, write permission to write changes to or remove it, and execute permission to run it as a program




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