EmbLogic » linux https://www.emblogic.com/blog Embedded System and ARM Training Tue, 03 Mar 2020 13:00:06 +0000 en-US hourly 1 http://wordpress.org/?v=3.9.1 What is Character Driver? https://www.emblogic.com/blog/02/what-is-character-driver/ https://www.emblogic.com/blog/02/what-is-character-driver/#comments Sun, 21 Feb 2016 12:10:16 +0000 http://www.emblogic.com/blog/?p=13296 Continue reading →]]> A character device driver is one that transfers data directly to and from a user process.

This is the most common type of device driver and there are plenty of simple examples in the source tree.

Character device drivers may transfer data between a user-level process and the device using any scheme other than the system buffer cache.

Character drivers control devices such as :-

 

——————————————

* network cards

* terminal devices

* printers

* specialized devices such as robots

* medical devices

* retail sales devices.

]]> https://www.emblogic.com/blog/02/what-is-character-driver/feed/ 0 ls – list command https://www.emblogic.com/blog/02/ls-list-command/ https://www.emblogic.com/blog/02/ls-list-command/#comments Wed, 10 Feb 2016 17:20:32 +0000 http://www.emblogic.com/blog/?p=13262 Continue reading →]]> ls – list command
=================
- ls means list directory content
- Prototype :
ls [OPTION] … [FILE] …
- Exit status
It returns 0 ,on success
Returns 1 in case of minor problems (eg. cannot access subdirectory)
returns 2 in case of serious trouble (eg. Cannot access command line argument)
- For specific listing you can use *
eg.1) For listing all files starting with a use :
ls a*
2) for listing all .c files use :
ls *.c
3) for listing all .c files starting with a use :
ls a*.c
- Some common options are :
i) -a –all –> Do not ignore enteries starting with .
Use this to view swap or temporary files.
ii) -l –> long listing format
iii) -r –) Reverse order sort (by name) and list
iv) -s –size –> Print allocated size of each file in blocks
v) -S –> Sort by file size
vi) -t –> Sort by modification time, newest first
vii) -U –> Do not sort; list enteries in directory order
viii) -X –> Sort alphabetically by entry extension.
ix) -F –> to distinguish files from directories (Puts / in directory and * with executable files)
x) -R –> It shows files that are contained in directory. It continued to dirrectory in a directory and so on.

- In fedora for long lsting use command :

ll

 

]]> https://www.emblogic.com/blog/02/ls-list-command/feed/ 0 Common linux virtual directories https://www.emblogic.com/blog/02/common-linux-virtual-directories/ https://www.emblogic.com/blog/02/common-linux-virtual-directories/#comments Tue, 09 Feb 2016 15:00:57 +0000 http://www.emblogic.com/blog/?p=13258 Continue reading →]]> Common Linux Virtual Directories
=================================
Directory               Usage
/ Root                     of virtual directory. No files are placed here (normally)
/bin                         Binary directory.GNU user level utilities are stored
/boot                       Boot directory.Boot files are stored here
/dev                         device directory, where linux creates device nodes
/etc                          system configuration files directory
/home                      home directory, user directories are placed here
/lib                          System & application library files are stored here
/media                   Common place for mount point of removable media
/mnt                        mount directory, for removable devices
/opt                         used to store optional software packages
/root                       home directory of root user
/sbin                      GNU admin level utilities are store here
/tmp                       Temporary work files are created and destroyed
/usr                        User installed softwares directory
/var                         For frequently changing directory ,such as log files

]]> https://www.emblogic.com/blog/02/common-linux-virtual-directories/feed/ 0 Linux Filesystem https://www.emblogic.com/blog/02/linux-filesystem/ https://www.emblogic.com/blog/02/linux-filesystem/#comments Tue, 09 Feb 2016 14:56:41 +0000 http://www.emblogic.com/blog/?p=13255 Continue reading →]]> Linux Filesystem
================
- In windows, physical drive determines the pathname of the file.
- Windows assigns a letter to each disk drive.
- Each directory contains its own directory structure for accesing files stored in it.
- For eg. in windows filepath is as:
c:\Users\ankur\Documents\Lessons.doc

- Linux does not use drive letters in pathnames like windows.
- Linux stores files within a single directory structure, called a virtual directory.
- Virtual directory contains filepaths from all storage devices installed on PC, mergedinto a single directory.
- There is a single base directory, called the root.
- root drive contains core of virtual directory.
- On root drive, Linux has special directories called mount points.
-When we start a new shell prompt, your session starts in your home directory.

]]> https://www.emblogic.com/blog/02/linux-filesystem/feed/ 0 How to get help in Linux – Fedora https://www.emblogic.com/blog/02/how-to-get-help-in-linux-fedora/ https://www.emblogic.com/blog/02/how-to-get-help-in-linux-fedora/#comments Tue, 09 Feb 2016 14:54:58 +0000 http://www.emblogic.com/blog/?p=13253 Continue reading →]]> To get help in fedora
=====================
To learn about any new command, function or utility in Fedora we can get help from it.
It has 3 such commands :-

i) man pages – These are manual pages .
- It contains interface to online reference manuals
- Press q to exit.
- How to Use ( Command ) – man command_name
- for all man pages of BASH shell, use
man bash
- It generally contains following information about command(command_name) :-
* Name
* Synopsis (Prototype)
* Description (Options)
* Author (author of command)
* Reporting Bugs (Feedback emails/Website)
* Copyright (copyright details)
* See Also (for further reference of command)

ii) Info pages – Read info documents
- It contains BASH manuals.
- Press q to exit
- How to Use (command) – info command_name
- It contains information about :-
* Prototype
* Introduction
* Options
* Exit Status
iii) help command
- It gives basic help for using a command and its various options.
- It gives output on Standard Output.
- It do not require exit command.
- How to Use (command) – help command_name
- It contains following information about command (command_name) :-
* Function of command
* Options
* Exit status

eg.
man echo
info echo
help echo

- To check total no. of enteries in each of three
I) type either of three (with space at end)
II) Press tab button for 3-4 times.
We will get the total number of possible options defined or list of them also.
eg. (<tab> means Press tab button)
man <tab><tab><tab>

]]> https://www.emblogic.com/blog/02/how-to-get-help-in-linux-fedora/feed/ 0 How to change default prompt in BASH shell https://www.emblogic.com/blog/02/how-to-change-default-prompt-in-bash-shell/ https://www.emblogic.com/blog/02/how-to-change-default-prompt-in-bash-shell/#comments Sun, 07 Feb 2016 15:46:40 +0000 http://www.emblogic.com/blog/?p=13238 Continue reading →]]> To change default prompt :-
========================
- We can change default prompt by assigning the character to it.
- Each character have a specific meaning.

BASH Shell Prompt Characters :-
Character Description
\a Bell Character
\d Date in format “Day Month Date”
\e ASCII escape character
\h Local hostname
\H Fully qualified domain hostname
\j Number of jobs currently managed by the shell
\l Basename of the shell’s terminal device name
\n ASCII newline character
\r ASCII carriage return
\s Name of the shell
\t Current time in 24-hour HH:MM:SS format
\T Current time in 12-hour HH:MM:SS format
\@ Current time in 12-hour am/pm format
\u Username of current user
\v Version of BASH shell
\V Release level of bash shell
\w Current working directory
\W Basename of current working directory
\# Command number of this command
\$ A dollar sign if normal user, #(Pound) for root user
/nnn Character corresponding to value nnn
\\ Backslash
\[ Begins a control code sequence
/] Ends a control code sequence

eg.
[ankur@(none) ~]$ PS1 = “[\t][\u]$”
[15:20:30][ankur]$

]]> https://www.emblogic.com/blog/02/how-to-change-default-prompt-in-bash-shell/feed/ 0 Command line Prompt – PS1, PS2 https://www.emblogic.com/blog/02/command-line-prompt-ps1-ps2/ https://www.emblogic.com/blog/02/command-line-prompt-ps1-ps2/#comments Sun, 07 Feb 2016 15:44:42 +0000 http://www.emblogic.com/blog/?p=13236 Continue reading →]]> Command line Prompt
===================
Environmental variables that controls Command line Prompt
PS1 : Controls the format of default command line prompt.
PS2 : Controls the format of second-tier command line prompt.
PS3 : Controls the format of tertiary command line prompt.

- Shell uses default PS1 prompt for initial data entry into shell.
- If we enter a command that requires additional information, shell displays second-tier prompt specified by PS2 .
- To display current settings for prompt use command :
echo $PS1
echo $PS2
- PS3 is used only in shell scripts.

]]> https://www.emblogic.com/blog/02/command-line-prompt-ps1-ps2/feed/ 0 Linux Run Levels https://www.emblogic.com/blog/02/linux-run-levels/ https://www.emblogic.com/blog/02/linux-run-levels/#comments Tue, 02 Feb 2016 12:36:51 +0000 http://www.emblogic.com/blog/?p=13216 Continue reading →]]> Linux Run Levels
================
Run Level    Description
0                    Halt
1                     Single-User mode
2                    Multi-user mode, usually without networking support
3                    Full multi-user mode with networking
4                    Unused
5                    Multiuser mode with networking and a graphical X window Session
6                    Reboot

- To change run level use init command

init run_level
- Most normal is run level 5 for graphical linux system.
- Level 1 is used for troubleshooting or emergency purpose.
- Most linux softwares start the network softwares at run level 3.
- What aplications work at Run level is determined by system by RC script.

]]> https://www.emblogic.com/blog/02/linux-run-levels/feed/ 0 Boot process of linux https://www.emblogic.com/blog/02/boot-process-of-linux/ https://www.emblogic.com/blog/02/boot-process-of-linux/#comments Tue, 02 Feb 2016 12:27:09 +0000 http://www.emblogic.com/blog/?p=13214 Continue reading →]]> The boot process of linux
=========================
- After you turn on your Linux System, linux kernel loads into memory and runs.
- Firstly, it runs the init process.
- init program is usually located at /sbin/init.
- init process has PID 1.
- The init process then starts all other processes.
- The init process reads the /etc/inittab file during boot (This is outdated now).

]]> https://www.emblogic.com/blog/02/boot-process-of-linux/feed/ 0 Sockets – Basics https://www.emblogic.com/blog/01/sockets-basics/ https://www.emblogic.com/blog/01/sockets-basics/#comments Sun, 31 Jan 2016 09:29:56 +0000 http://www.emblogic.com/blog/?p=13210 Continue reading →]]> Sockets
=======
A socket is a communication mechanism that allows client/server systems to be developed either locally,on a single machine, or across networks.
- It is a communication mechanism
- It allows client/server systems to developed either locally or across a network.
- Socket is an extension of pipe
- They make clear distinction between client and server.
- Socket can be named or unnamed.
- They make clear distinction between server and client.
- In a socket, one side is client/server for read/write/both and other side is a network interface.

There are 6 tasks in a socket :-
1. Create Socket.
2. Give name to socket.
3. Listen to socket for incoming connection.
4. Coonect the client to server.
5. Accept the request by server from client.
6. Close the socket

]]> https://www.emblogic.com/blog/01/sockets-basics/feed/ 0 Basic linklist operations https://www.emblogic.com/blog/01/basic-linklist-operations/ https://www.emblogic.com/blog/01/basic-linklist-operations/#comments Sat, 16 Jan 2016 07:07:03 +0000 http://www.emblogic.com/blog/?p=13182 Continue reading →]]> RCS file: header.h,v
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]]> https://www.emblogic.com/blog/01/basic-linklist-operations/feed/ 0 How to Send a signal -Using Kill command https://www.emblogic.com/blog/01/how-to-send-a-signal-using-kill-command/ https://www.emblogic.com/blog/01/how-to-send-a-signal-using-kill-command/#comments Fri, 15 Jan 2016 12:01:08 +0000 http://www.emblogic.com/blog/?p=13175 Continue reading →]]> Send a signal by Kill command
=======================
- To send a signal to a process other than current task.
- It has prototype :-
int kill(pid_t pid, int signo);
- It is included using header :-
#include<signal.h>
- The system data type pid_t is defined in header :-
#include<sys/types.h>
- signo is the signal number of signal to be send.
- pid is the PID of the process to which signal is to be send.
- pid can take value:-
* 0 –> To send signo signal to every process in invoking process’ process group
* -1 –>To send signo signal to every process for which invoking process has permission to send a signal, except itself and init
* n(<-1) –> All process in process group
* n(>0)  –> process with PID n is signalled.
- This take an optional signal name or number and the PID to send the signal.

- For eg. To send ‘hangup’ signal to shell running on PID 1001, we use command :-
kill(1001,HUP);
- killall is used to send signal to all the processes running.

]]> https://www.emblogic.com/blog/01/how-to-send-a-signal-using-kill-command/feed/ 0 How to register a signal https://www.emblogic.com/blog/01/how-to-register-a-signal/ https://www.emblogic.com/blog/01/how-to-register-a-signal/#comments Fri, 15 Jan 2016 11:59:04 +0000 http://www.emblogic.com/blog/?p=13173 Continue reading →]]> Register a signal
==================
- Program can handle a signal using signal library function signal().
- signal() is used to register the signal handler function with kernel on behalf of current process.
- It is included in header :-
#include<header.h>
- Prototype of function is :-
void* (signal(int signo,void(*func)(int)))(int);
- signal() function takes 2 parameters, signo and func.
- The signal to be caught or ignored is given as argument signo.
- The function to be called when the specified signal is received is given as func.
- The function must take a single int argument (the signal received) and has return type void.

- The signal() command can be used in 3 modes :-
(i) Default mode (Terminate the process)
SIG_DFL –> is used in place of func.
(ii) Ignore the signal
SIG_IGN –> is used in place of func.
(iii) User defined mode
User defined function is used in place of func.

- The signal command returns the function which is setup to handle the signal, SIG_DFL or SIG_IGN in 3rd, 1st and 2nd cases respectively.

]]> https://www.emblogic.com/blog/01/how-to-register-a-signal/feed/ 0 About Signals https://www.emblogic.com/blog/01/about-signals/ https://www.emblogic.com/blog/01/about-signals/#comments Fri, 15 Jan 2016 11:57:12 +0000 http://www.emblogic.com/blog/?p=13171 Continue reading →]]> Signals
========
- A signal is an event generated by UNIX/LINUX system in response to some condition.
- On receipt of a signal, process may in turn take some action.
- Signals are generated by some error conditions such as:-
* Memory Segment Violation
* Floating Point Processor error
* Illegal Instruction etc.
- They are generated by shell and terminal handlers.
- They cause interrupts.

- They can also be used to sent from one process to another as a way of passing information or modifying behaviour.

- As default, if a process receives any signal, process will be terminated immediately.
- Usually a core dump file is created.

- The signals are defined by including header file signal.h
- They all begn with “SIG”.
- There are 64 signals in LINUX.
- The can be listed using command :-
kill -l
- Some of the signals are :-

Signal Name       Description
SIGABORT          Process Abort
SIGALRM           Alarm Clock
SIGFPE            Floating Point Exception
SIGHUP            Hangup
SIGILL            Illegal Instruction
SIGINT            Terminal Interrupt
SIGKILL           Kill (can’t be caught or ignored)
SIGPIPE           Write on a pipe with no reader
SIGQUIT           Terminal Quit
SIGSEGV           Invalid memory segment access (Segmentation Fault)
SIGTERM           Termination
SIGUSR1           User-defined signal 1
SIGUSR2           User-defined signal 2

SIGCHLD           Child process has stopped or exited
SIGCONT           Continue exexuting, if stopped
SIGSTOP           Stop Executing (Can’t be caught or ignored)
SIGTSTP           Terminal stop signal
SIGTTIN           Background process trying to read
SIGTTOU           Background process trying to write

- SIGINT can be called using Ctrl-C
- A signal has 3 steps:-
1) raise
2) catch
3) ignore/handle

]]> https://www.emblogic.com/blog/01/about-signals/feed/ 0 Replacing a Process Image https://www.emblogic.com/blog/01/replacing-a-process-image/ https://www.emblogic.com/blog/01/replacing-a-process-image/#comments Fri, 15 Jan 2016 10:40:34 +0000 http://www.emblogic.com/blog/?p=13167 Continue reading →]]> Replacing a Process Image
=========================
- The exec function replaces current process with a new process.
- The path of new process is specified as argument to exec.
- It is defined in header :
#include<unistd.h>
- Last argument of function should be NULL.
- It has 6 types of functions, whose prototype are :-
(i) Complete path is specified
int execl(const char * path, const char * arg0,const char * arg1,…,NULL);
(ii) If file is at one of default paths
int execlp(const char * file, const char * arg0,const char * arg1,…,NULL);
(iii) If arguments are given as an vector(array)
int execv(const char *path,char *const argv[]);
(iv) If arguments are given as an vector(array) and file is at one of default paths
int execvp(const char* file, char *const argv[]);
(v) int execle(const char *path, const char * arg0, const char * arg1,…,NULL, char *const envp[]);
(vi) int execve(const char *path, char *const argv[],char *const envp[] );

- The suffix p means to search PATH environmental variable.

- If the exec is executed successfully the statements after it will not be executed.
- It is because the current process is replaced.
- The arguments given to exec are used by main() function of new process as command line argument.
- If exec fails, it returns -1
- The open file descriptors remain open after the exec command.
- These file descriptors can be passed to exec as command and can be used by the replaced process to read/write from opened file.
- The argument is passed to exec as character.
- For this sprintf() is used.
- And for getting the file descriptors back , atoi() or integer typecasting can be used on the arguments of main().

]]> https://www.emblogic.com/blog/01/replacing-a-process-image/feed/ 0