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13. Copyright Considerations With LKMsA perennial question about LKMs is whether the terms of GPL apply to one, considering that the Linux kernel is distributed under GPL. For example, is it OK to ship an LKM in binary only form? This section covers the copyright issues surrounding LKMs, which are as interesting as they are complex. Fair warning: we don't reach a conclusion. The law is unsettled a

Next Previous Contents 8. Linux Networking 8.1 How Linux networking is managed? There exists a device driver for each kind of NIC. Inside it, Linux will ALWAYS call a standard high level routing: "netif_rx [net/core/dev.c]", which will controls what 3 level protocol the frame belong to, and it will call the right 3 level function (so we'll use a pointer to the function to determine which is right)

Returns true if... -efile exists -afile exists This is identical in effect to -e. It has been "deprecated," [1] and its use is discouraged. -ffile is a regular file (not a directory or device file) -sfile is not zero size -dfile is a directory -bfile is a block device -cfile is a character device device0="/dev/sda2" # / (root directory) if [ -b "$device0" ] then echo "$device0 is a block device."

Next Previous Contents 9. Inquiry Command Example One of the most basic SCSI commands is the INQUIRY command, used to identify the type and make of the device. Here is the definition from the SCSI-2 specification (for details refer to the SCSI-2 standard). Table 44: INQUIRY Command +=====-========-========-========-========-========-========-========-========+ | Bit| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0

Chapter 33. Options Options are settings that change shell and/or script behavior. The set command enables options within a script. At the point in the script where you want the options to take effect, use set -o option-name or, in short form, set -option-abbrev. These two forms are equivalent.

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David S. Lawyer mailto:dave@lafn.org v1.43 March 2013 This document was originally written for real text terminals which were like monitors (with keyboards), but could only display text with a command line interface (no pictures). They were widely used to access mainframe computers in the late 1970's and 1980's but use of them declined in the 1990's and they are seldom used anymore. However much o

8. SMP Boot There are a few SMP related macros, like CONFIG_SMP, CONFIG_X86_LOCAL_APIC, CONFIG_X86_IO_APIC, CONFIG_MULTIQUAD and CONFIG_VISWS. I will ignore code that requires CONFIG_MULTIQUAD or CONFIG_VISWS, which most people don't care (if not using IBM high-end multiprocessor server or SGI Visual Workstation). BSP executes start_kernel() -> smp_init() -> smp_boot_cpus() -> do_boot_cpu() -> wak

This document describes the TCP keepalive implementation in the linux kernel, introduces the overall concept and points to both system configuration and software development. Table of Contents1. Introduction1.1. Copyright and License1.2. Disclaimer1.3. Credits / Contributors1.4. Feedback1.5. Translations2. TCP keepalive overview2.1. What is TCP keepalive?2.2. Why use TCP keepalive?2.3. Checking fo

4. Linux Directory Hierarchy: Oriented to the Software PartsBy now, all discussion are OS independent. On Linux, the Four Software Parts theory is expressed in his directory structure, which is classified and documented in the Filesystem Hierarchy Standard. The FHS is part of the LSB (Linux Standard Base), which makes him a good thing because all the industry is moving thowards it, and is a consta

Next Previous Contents 3. Virtuald 3.1 Introduction Every network connection is made up of two IP address/port pairs. The API (Applications Program Interface) for network programming is called the Sockets API. The socket acts like an open file and by reading/writing to it you can send data over a network connection. There is a function call getsockname that will return the IP address of the local

Chapter 13. Arithmetic ExpansionArithmetic expansion provides a powerful tool for performing (integer) arithmetic operations in scripts. Translating a string into a numerical expression is relatively straightforward using backticks, double parentheses, or let.

Builtin variables:variables affecting bash script behavior $BASHThe path to the Bash binary itself $BASH_ENVAn environmental variable pointing to a Bash startup file to be read when a script is invoked $BASH_SUBSHELLA variable indicating the subshell level. This is a new addition to Bash, version 3. See Example 21-1 for usage. $BASHPIDProcess ID of the current instance of Bash. This is not the sam

This document outlines the set of requirements and guidelines for file and directory placement under the Linux operating system according to those of the FSSTND v2.3 final (January 29, 2004) and also its actual implementation on an arbitrary system. It is meant to be accessible to all members of the Linux community, be distribution independent and is intended to discuss the impact of the FSSTND an

This document describes the working basics of PC-class computers, Unix-like operating systems, and the Internet in non-technical language. Table of Contents1. Introduction1.1. Purpose of this document1.2. New versions of this document1.3. Feedback and corrections1.4. Related resources2. Basic anatomy of your computer3. What happens when you switch on a computer?4. What happens when you log in?5. W

2. TCP keepalive overview In order to understand what TCP keepalive (which we will just call keepalive) does, you need do nothing more than read the name: keep TCP alive. This means that you will be able to check your connected socket (also known as TCP sockets), and determine whether the connection is still up and running or if it has broken. 2.1. What is TCP keepalive? The keepalive concept is v

This document describes the TCP keepalive implementation in the linux kernel, introduces the overall concept and points to both system configuration and software development. Table of Contents1. Introduction1.1. Copyright and License1.2. Disclaimer1.3. Credits / Contributors1.4. Feedback1.5. Translations2. TCP keepalive overview2.1. What is TCP keepalive?2.2. Why use TCP keepalive?2.3. Checking fo

A very hands-on approach to iproute2, traffic shaping and a bit of netfilter. Table of Contents1. Dedication2. Introduction2.1. Disclaimer & License2.2. Prior knowledge2.3. What Linux can do for you2.4. Housekeeping notes2.5. Access, CVS & submitting updates2.6. Mailing list2.7. Layout of this document3. Introduction to iproute23.1. Why iproute2?3.2. iproute2 tour3.3. Prerequisites3.4. Exploring y

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7.1.1. GeneralAt times you need to specify different courses of action to be taken in a shell script, depending on the success or failure of a command. The if construction allows you to specify such conditions. The most compact syntax of the if command is: if TEST-COMMANDS; then CONSEQUENT-COMMANDS; fi The TEST-COMMAND list is executed, and if its return status is zero, the CONSEQUENT-COMMANDS lis

This HOWTO for programmers discusses how to create and use program libraries on Linux. This includes static libraries, shared libraries, and dynamically loaded libraries. Table of Contents1. Introduction2. Static Libraries3. Shared Libraries3.1. Conventions3.2. How Libraries are Used3.3. Environment Variables3.4. Creating a Shared Library3.5. Installing and Using a Shared Library3.6. Incompatible

3.1.1.1. GeneralA simple description of the UNIX system, also applicable to Linux, is this: "On a UNIX system, everything is a file; if something is not a file, it is a process." This statement is true because there are special files that are more than just files (named pipes and sockets, for instance), but to keep things simple, saying that everything is a file is an acceptable generalization. A

Appendix B. Reference CardsThe following reference cards provide a useful summary of certain scripting concepts. The foregoing text treats these matters in more depth, as well as giving usage examples.

2.3.1. Debugging on the entire scriptWhen things don't go according to plan, you need to determine what exactly causes the script to fail. Bash provides extensive debugging features. The most common is to start up the subshell with the -x option, which will run the entire script in debug mode. Traces of each command plus its arguments are printed to standard output after the commands have been exp

Table E-1. Reserved Exit Codes Exit Code NumberMeaningExampleComments

Next Previous Contents 4. Examples for different shells Below we provide an set of examples for some of the more common shells. We start with zsh as it provides several facilities that make our job much easier. We will then progress through increasingly difficult examples. In all the examples we test the environment variable $TERM to make sure we only apply the escapes to xterms. We test for $TERM