Advanced programming in linux

Advanced programming in Linux environment

Ssize_t signed type, (typedef definition)

View the limit of the maximum number of open files (ulimit -a)

View the maximum number of files allowed in the current system cat /proc/sys/fs/file-max

File descriptor

Error header file errno value

When the error is reported, the error code is written to errno, strerror(errno) can get the wrong explanation, and perror() can also get the wrong explanation.

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20 Advanced Commands for Linux Experts

Thanks for all the likes, good words and support you gave us in the first two part of this article. In the first article we discussed commands for those users who have just switched to Linux and needed the necessary knowledge to start with.

In the second article we discussed the commands which a middle level user requires to manage his own system.

What Next? In this article I will be explaining those commands required for administrating the Linux Server.

Linux Expert Commands

41. Command: ifconfig

ifconfig is used to configure the kernel-resident network interfaces. It is used at boot time to set up interfaces as necessary. After that, it is usually only needed when debugging or when system tuning is needed.

Check Active Network Interfaces

Check All Network Interfaces

Display details of All interfaces including disabled interfaces using “-a” argument.

Disable an Interface

Enable an Interface

Assign IP Address to an Interface

Assign “192.168.1.12” as the IP address for the interface eth0.

Change Subnet Mask of Interface eth0

Change Broadcast Address of Interface eth0

Assign IP Address, Netmask and Broadcast to Interface eth0

Note: If using a wireless network you need to use command “iwconfig“. For more “ifconfig” command examples and usage, read 15 Useful “ifconfig” Commands.

42. Command: netstat

netstat command displays various network related information such as network connections, routing tables, interface statistics, masquerade connections, multicast memberships etc.

List All Network Ports

List All TCP Ports

Show Statistics for All Ports

OK! For some reason if you want not to resolve host, port and user name as a output of netstat.

Fine, you may need to get the output of netstat continuously till interrupt instruction is passed (ctrl+c).

For more “netstat” command examples and usage, see the article 20 Netstat Command Examples.

43. Command: nslookup

A network utility program used to obtain information about Internet servers. As its name suggests, the utility finds name server information for domains by querying DNS.

Query Mail Exchanger Record

Query Name Server

Query DNS Record

Query Start of Authority

Query Port Number

Change the port number using which you want to connect

44. Command: dig

dig is a tool for querying DNS nameservers for information about host addresses, mail exchanges, nameservers, and related information. This tool can be used from any Linux (Unix) or Macintosh OS X operating system. The most typical use of dig is to simply query a single host.

Turn Off Comment Lines

Turn Off Authority Section

Turn Off Additional Section

Turn Off Stats Section

Turn Off Answer Section

Disable All Section at Once

45. Command: uptime

You have just connected to your Linux Server Machine and founds Something unusual or malicious, what you will do? Guessing…. NO, definitely not you could run uptime to verify what happened actually when the server was unattended.

46. Command: wall

one of the most important command for administrator, wall sends a message to everybody logged in with their mesg permission set to “yes“. The message can be given as an argument to wall, or it can be sent to wall’s standard input.

47. command: mesg

Lets you control if people can use the “write” command, to send text to you over the screen.

48. Command: write

Let you send text directly to the screen of another Linux machine if ‘mesg’ is ‘y’.

49. Command: talk

An enhancement to write command, talk command lets you talk to the logged in users.

Note: If talk command is not installed, you can always apt or yum the required packages.

50. Command: w

what command ‘w’ seems you funny? But actually it is not. t’s a command, even if it’s just one letter long! The command “w” is a combination of uptime and who commands given one immediately after the other, in that order.

51. Command: rename

As the name suggests, this command rename files. rename will rename the specified files by replacing the first occurrence from the file name.

Just type the command.

52. Command: top

Displays the processes of CPU. This command refresh automatically, by default and continues to show CPU processes unless interrupt-instruction is given.

53. Command: mkfs.ext4

This command create a new ext4 file system on the specified device, if wrong device is followed after this command, the whole block will be wiped and formatted, hence it is suggested not to run this command unless and until you understand what you are doing.

54. Command: vi/emacs/nano

vi (visual), emacs, nano are some of the most commonly used editors in Linux. They are used oftenly to edit text, configuration,… files. A quick guide to work around vi and nano is, emacs is a.

vi-editor

[press ‘i’ to enter insert mode, or you won’t be able to type-in anything]

alt+x (exit insert mode, remember to keep some space between the last letter.
ctrl+x command or your last word will be deleted).
:wq! (saves the file, with the current text, remember ‘!’ is to override).

nano editor

ctrl +x (to close the editor). It will show output as:

Click ‘y’ to yes and enter file name, and you are done.

55. Command: rsync

Rsync copies files and has a -P switch for a progress bar. So if you have rsync installed, you could use a simple alias.

Now try to copy a large file in terminal and see the output with remaining items, similar to a progress bar.

Moreover, Keeping and Maintaining backup is one of the most important and boring work a system administrator, needs to perform. Rsync is a very nice tool (there exists, several other) to create and maintain backup, in terminal.

Note: -z for compression, -v for verbose and -r for recursive.

56. Command: free

Keeping track of memory and resources is as much important, as any other task performed by an administrator, and ‘free‘ command comes to rescue here.

Current Usage Status of Memory

Tuned Output in KB, or MB, or GB

Check Current Usage in Human Readable Format

Check Status Contineously After Regular Interval

57. Command: mysqldump

Ok till now you would have understood what this command actually stands for, from the name of this command.mysqldump commands dumps (backups) all or a particular database data into a given a file.For example,

Note: mysqldump requires mysql to be running and correct password for authorisation. We have covered some useful “mysqldump” commands at Database Backup with mysqldump Command

58. Command: mkpasswd

Make a hard-to-guess, random password of the length as specified.

Note: -l 10 generates a random password of 10 characters while -l 20 generates a password of character 20, it could be set to anything to get desired result. This command is very useful and implemented in scripting language oftenly to generate random passwords. You might need to yum or apt the ‘expect’ package to use this command.

59. Command: paste

Merge two or more text files on lines using. Example. If the content of file1 was:

60.Command: lsof

lsof stands for “list open files” and displays all the files that your system has currently opened. It’s very useful to figure out which processes uses a certain file, or to display all the files for a single process. Some useful 10 lsof Command examples, you might be interested in reading.

This is not the end, a System Administrator does a lot of stuff, to provide you such a nice interface, upon which you work. System Administration is actually an art of learning and implementing in a very much perfect way. We will try to get you with all other necessary stuff which a linux professional must learn, linux in its basic actually itself, is a process of learning and learning. Your good words are always sought, which encourages us to put in more effort to give you a knowledgeable article. “Like and share Us, to help Us Spread”.

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Advanced programming in linux

In this course, students will learn to develop complex system-level software in the C programming language while gaining an intimate understanding of the Unix operating system (and all OS that belong to this family, such as Linux, the BSDs, and even Mac OS X) and its programming environment.

Topics covered will include the user/kernel interface, fundamental concepts of Unix, user authentication, basic and advanced I/O, fileystems, signals, process relationships, and interprocess communication. Fundamental concepts of software development and maintenance on Unix systems (development and debugging tools such as «make» and «gdb») will also be covered.

Students are expected to have a good working knowledge of the C programming language, have written non-trivial programs before, and to be able to competently use a Unix system with a command-line shell interface. All coursework will be done exclusively on a Unix system from the command-line. This is not an introduction to using Unix!

If you email me to waive the prerequisites, please provide information about how you meet the requirements listed above in bold. (This has the added benefit of showing that you’ve actually read at least this far on this page.)

This class overlaps significantly with CS392 «Systems Programming» — if you have taken this class, please talk to me in person before trying to register for CS631.

Time, Date & Place:

Interactive/synchronous: Mondays, 18:30 Eastern, North Building 101 or via Zoom
Online on-demand: anytime via YouTube video lectures

Instructor:

When emailing me, please use your @stevens.edu address. I will likely not even see your email if it is sent from gmail or any other non-stevens address.

Resources:

Content and discussions:

CS631APUE Mailinglist
Note: all class communications happen via this mailing list.
All registered students are subscribed to this list using their @stevens.edu address. It is critical that you read this list.
Course Slack
Course Videos / Youtube Channel (RSS feed)

Tool Tips:

ctags(1) [slides] [transcript]
screen(1) [slides] [transcript]
/usr/share/docs [slides] [transcript]

Tweets by @cs631apue

Source Code

You will be writing a lot of code in this class. You may also find the need to read a lot of code not written by you as well as the manual pages accompanying the sources.

Our primary reference platform being NetBSD, you can install the full sources into your VM via e.g., this script.

To browse or fetch sources for other Open Source Unix variations, please see these links:

Textbooks:

The textbook used in this class is:

« Advanced Programming in the UNIX® Environment», Third Edition
W. Richard Stevens, Stephen A. Rago
ISBN: 0-321-63773-9
Publisher: Addison Wesley Professional
Code Examples | Safari Online version

The following books are recommended purely for your own personal reference. They’re not used in the class as a text, but are related and very useful books to have:

«The C Programming Language» — important : make sure you get the 2nd Edition covering ANSI C .
by Brian W. Kernighan and Dennis M. Ritchie.
Prentice Hall, Inc., 1988.
ISBN 0-13-110362-8 (paperback), 0-13-110370-9 (hardback).
«The Practice of Programming»
by Brian W. Kernighan and Rob Pike.
Addison-Wesley, Inc., 1999.
ISBN 0-201-61586-X.

Systems Used

All software development will be done on a NetBSD system. It is your responsibility to gain access to such a system prior to the start of the class. Please see this page for more information. Instructions on how to install NetBSD in a VirtualBox VM are provided to you here.

All grading will be done on a NetBSD 9.2 system. While you may choose to develop on your own personal host, you should make sure that your code compiles and runs flawlessly on this OS version.

You may also find it useful to get yourself an account on the Stevens linux-lab systems to be able to compare another system.

Grading:

Plagiarism, Cheating and other ways to get an F

Students are responsible for their own work. It is unethical (and in some cases illegal) to present as one’s work the ideas, words or representations of another without the proper indication of the source. Therefore, it is the student’s responsibility to give credit for any quotation, idea or data (such as statistical data or source code) borrowed from an outside source.

Failure to do so constitutes plagiarism, may imply copyright infringement and license violations and is viewed as cheating in this class.

Homework Assignments:

Assignments will be posted as the semester progresses.

The following exercises are not graded, but are recommended to be completed before or soon after the given lecture to help you better understand the concepts dicussed.

Midterm Project:

Implement the «ls(1)» command as decribed in the manual page provided to you. See the full midterm project description for details.

Group Project:

Implement the «sws(1)» command as decribed in the manual page provided to you. See the full group project description for details.

Details to be announced.

In 2012, we had a take-home final. The final may differ in the coming semester. —>

Homework assignments, slides, and other material listed below are from the previous semester. We will update the content as the semester progresses.

Date	Topic	Reading	Links
2021-08-30	Introduction, UNIX history, UNIX Programming Basics	Stevens: Chapters 1, 2 Unix history and basic features	Week 01, Segment 1: Introduction [slides] [transcript]

Date

Topic

Reading

Links

2021-08-30

Introduction, UNIX history, UNIX Programming Basics

Stevens: Chapters 1, 2
Unix history and basic features

Week 01, Segment 1: Introduction
[slides] [transcript]

Week 01 Checkpoint
2021-09-06 Labor Day Holiday 2021-09-13 File I/O, File Sharing Stevens: Chapter 3 Week 02, Segment 1: File Descriptors
[slides] [transcript]

HW1: bbcp(1)

2021-09-20 Files and Directories Stevens: Chapter 4 Week 03, Segment 1: stat(2) intro
[slides] [transcript]

Week 03 Checkpoint
Midterm Project Assignment 2021-09-27 Filesystems, System Data Files, Time & Date Stevens: Chapter 4, 6
File Systems and Storage Models: 4.4.1, 4.5 — 4.7 Week 04, Segment 1: The Unix Filesystem
[slides] [transcript]

Week 04 Checkpoint
Zoom Meeting Recording

2021-10-04 UNIX tools: cc(1), make(1), revision control, diff(1), patch(1), gdb(1) CVS Documentation
Mini FAQ about the misc libc/gcc crt files
Debugging with GDB
Guide to Faster, Less Frustrating Debugging
gdb Tutorial
Git Week 05, Segment 1: The Unix Development Environment
[slides] [transcript]

Week 05, Segment 4: The Compiler Toolchain, Part II
[slides] [transcript]

Week 05, Segment 5: The Compiler Toolchain, Part III
[slides] [transcript]

Week 05, Segment 6: The Compiler Toolchain, Part IV
[slides] [transcript]

2021-10-11 Fall Recess 2021-10-12 Process Environment, Process Control Stevens: Chapters 7, 8
Smashing The Stack For Fun And Profit
Linux x86 Program Start Up
stdarg And The Case Of The Forgotten Registers Note: Tuesday Class

Week 06, Segment 5: Process Limits and Identifiers
[slides] [transcript]

Week 06 Checkpoint
2021-10-18 Process Groups, Sessions, Signals Stevens: Chapter 9, 10
POSIX Terminal Interface Description
Shichao’s Notes
FreeBSD Process Management (from «The Design and Implementation of the FreeBSD Operating System»)

Week 07, Segment 1: The Login Process
[slides] [transcript]

Week 07, Segment 5: Reentrant and Interrupted Functions
[slides] [transcript]

eintr.c
pending.c
reentrant.c
signals1.c
signals2.c
signals3.c
signals4.c
sigusr.c 2021-10-25 Interprocess Communication I Stevens: Chapter 14
Shared Memory Introduction
Semaphores in Linux
Interprocess communication using POSIX message queues in Linux

Week 08, Segment 1: Interprocess Communications Intro
[slides] [transcript]

HW#2: implement ‘command(3)’
2021-11-01 Interprocess Communication II Stevens: Chapter 14
BSD IPC
How Linux creates sockets and counts them
How Linux allows TCP introspection
The C10K problem
Week 09, Segment 1: socketpair(2)
[slides] [transcript]

Group Project Assignment
2021-11-08 Dæmon Processes, HTTP / Group Project Discussions Week 10, Segment 1: Dæmon Processes
[slides] [transcript]

Lecture Slides 2021-11-15 Shared Libraries Stevens: Chapter 13
How to read an Executable
Ian Lance Taylor’s blog post series on linkers
Linkers and Loaders
How To Write Shared Libraries
The Executable and Linkable Format (ELF) Week 11, Segment 1: The Executable and Linkable Format
[slides] [transcript]

crypt.c
dlopenex.c
evil.c
hello.c
ldtest1.2.c
ldtest1.c
ldtest2.c
main.c
setget.c
libgreet exercise

2021-11-22 Advanced I/O: Nonblocking I/O, Polling, and Record Locking / Encryption in a Nutshell Stevens: Chapter 14 Week 12, Segment 1: syslog(3)
[slides] [transcript]

Week 12, Segment 4: Asynchronous and Memory Mapped I/O
[slides] [transcript]

Lecture Slides (previous semester, includes section on encryption basics)

2021-11-29 Restricting processes / Containers Course Notes
Thread scheduling and related interfaces in NetBSD 5.0
CPU Pinning and CPU Sets Week 13, Segment 1: POSIX ACLs
[slides] [transcript]

Week 13, Segment 2: eUIDs, file flags, mount options, securelevels
[slides] [transcript]

Week 13, Segment 5: Processor Affinity and CPU Sets
[slides] [transcript]

Week 13, Segment 6: Capabilities, Control Groups, Containers
[slides] [transcript]

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