Rsync explained

Rsync (Remote Sync) is a most commonly used command for copying and synchronizing files and directories remotely as well as locally in Linux/Unix systems. With the help of rsync command you can copy and synchronize your data remotely and locally across directories, across disks and networks, perform data backups and mirroring between two Linux machines.…

The Differences Between MBR and GPT partitions

f you have dabbled with your hard disk and is always doing formatting and partitioning, you will surely come across the term “MBR” and “GPT”. This is especially evident when you are dual-booting your Mac and faced with the problem of having to switch from GPT to MBR. You probably are wondering, what are the…

Memory Management

Memory Management The memory management subsystem is one of the most important parts of the operating system. Since the early days of computing, there has been a need for more memory than exists physically in a system. Strategies have been developed to overcome this limitation and the most successful of these is virtual memory. Virtual…

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What is a block device and how do I resize it?

What is a block device A block device is a device you can read blocks from. For example hard disks, cdrom drives and floppies are block devices, but not the keyboard. You can receive data from the keyboard and regard them as blocks, but you cannot seek on the keyboard. You can tell a hard…

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Managing IP-Tbales

Overview Iptables is a rule-based firewall, which will process each rule in order until it finds one that matches. Todo: include example here Usage The iptables utility is typically pre-installed on your linux distribution, but isn’t actually running any rules. You’ll find the utility here on most distributions: /sbin/iptables Blocking a Single IP Address You…

RETRANSMISSION

TCP Segment Retransmission Timers and the Retransmission Queue 

TCP Transaction Example with Retransmission Let’s use an example to clarify how acknowledgments and retransmissions work in TCP (illustrated in Figure 223, to which you may wish to refer as you read on). Suppose the server in a connection sends out four contiguous segments (numbered starting with 1 for clarity): Segment #1:Sequence Number field is 1 and…

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IP address classes and structure

IP address classes and structure When the IEEE committee sat down to sort out the range of numbers that were going to be used by all computers, they came up with five different ranges or, as we call them, “classes” of IP addresses. When someone applies for IP addresses they are given a certain range…

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General Overview of Layer 2

General Overview of Layer 2 Layer 2 is Data Link Layer (DLL) as per OSI Model. As we know function of each layer is to provide services to above layer, so DLL provide various services to Layer 3: Network Layer. Various services which DLL provides are: Framing network layer data packets. Flow Control Multiple Access…

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$df and $du

With these two commands, not only can you discover details about the free space on the mounted file systems, but you can also see the amount of space used by individual directories. df The df command shows the disk space usage on all the currently mounted file systems. Here is what the output from running…

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$ps aux

Symptoms The ps command, for Process Status, displays a header line followed by lines containing information about the processes that are running on the IPSO platform. For example: [admin]# ps -aux USER PID %CPU %MEM VSZ RSS TT STAT STARTED TIME COMMAND root 6372 0.0 0.1 432 220 p0 R+ 3:15PM 0:00.02 ps -aux root…