File System Overview - Linux

File System Overview - Linux

 

1. bin : This folder contains all the executable binary programs (file) required during booting, repairing, files required to run into single-user-mode, and other important, basic commands - cat, du, df, tar, rpm, wc, history, etc.
2. /boot : Holds important files during boot-up process, including Linux Kernel.
3. /dev : Contains device files for all the hardware devices on the machine e.g., cdrom, cpu, etc
4. /etc : Contains Application’s configuration files, startup, shutdown, start, stop script for every individual program.
5. /home : Home directory of the users. Every time a new user is created, a directory in the name of user is created within home directory which contains other directories like Desktop, Downloads, Documents, etc.
6. /lib : The Lib directory contains kernel modules and shared library images required to boot the system and run commands in root file system.
7. /lost+found : This Directory is installed during installation of Linux, useful for recovering files which may be broken due to unexpected shut-down.
8. /media : Temporary mount directory is created for removable devices viz., media/cdrom.
9. /mnt : Temporary mount directory for mounting file system.
10. /opt : Optional is abbreviated as opt. Contains third party application software. Viz., Java, etc.
11. /proc : A virtual and pseudo file-system which contains information about running process with a particular Process-id aka pid.
12. /root : This is the home directory of root user and should never be confused with ‘/‘
13. /run : This directory is the only clean solution for early-runtime-dir problem.
14. /sbin : Contains binary executable programs, required by System Administrator, for Maintenance. Viz., iptables, fdisk, ifconfig, swapon, reboot, etc.
15. /srv : Service is abbreviated as ‘srv‘. This directory contains server specific and service related files.
16. /sys : Modern Linux distributions include a /sys directory as a virtual filesystem, which stores and allows modification of the devices connected to the system.
17. /tmp :System’s Temporary Directory, Accessible by users and root. Stores temporary files for user and system, till next boot.
18. /usr : Contains executable binaries, documentation, source code, libraries for second level program.
19. /var : Stands for variable. The contents of this file is expected to grow. This directory contains log, lock, spool, mail and temp files.

How to find which OS you are working on ?

       For some projects you will need to find out which OS you are working on or on which Operating System the code is deployed. This may be needed in certain cases like - File System Handling ,
Data upload system, Electronic Records System etc because the file organization of different operating systems are indifferent.

For the list of other system properties/ System environment variables please click here

       The following code sample in Java gives this -

 package com.util;  
 public class FindOS{  
      private static String OS = System.getProperty("os.name").toLowerCase();  
      public static void main(String[] args) {  
           System.out.println(OS);  
           if (isWindows()) {  
                System.out.println("This is Windows");  
           } else if (isMac()) {  
                System.out.println("This is Mac");  
           } else if (isUnix()) {  
                System.out.println("This is Unix or Linux");  
           } else if (isSolaris()) {  
                System.out.println("This is Solaris");  
           } else {  
                System.out.println("Your OS is not support!!");  
           }  
      }  
      public static boolean isWindows() {  
           return (OS.indexOf("win") >= 0);  
      }  
      public static boolean isMac() {  
           return (OS.indexOf("mac") >= 0);  
      }  
      public static boolean isUnix() {  
           return (OS.indexOf("nix") >= 0 || OS.indexOf("nux") >= 0 || OS.indexOf("aix") > 0 );  
      }  
      public static boolean isSolaris() {  
           return (OS.indexOf("sunos") >= 0);  
      }  
 }  

Linux Commands

File Commands
1.	ls	Directory listing
2.	ls -al	Formatted listing with hidden files
3.	ls -lt	Sorting the Formatted listing by time modification
4.	cd dir	Change directory to dir
5.	cd	Change to home directory
6.	pwd	Show current working directory
7.	mkdir dir	Creating a directory dir
8.	cat >file	Places the standard input into the file
9.	more file	Output the contents of the file
10.	head file	Output the first 10 lines of the file
11.	tail file	Output the last 10 lines of the file
12.	tail -f file	Output the contents of file as it grows,starting with
		the last 10 lines
13.	touch file	Create or update file
14.	rm file	Deleting the file
15.	rm -r dir	Deleting the directory
16.	rm -f file	Force to remove the file
17.	rm -rf dir	Force to remove the directory dir
18.	cp file1 file2	Copy the contents of file1 to file2
19.	cp -r dir1 dir2	Copy dir1 to dir2;create dir2 if not present
20.	mv file1 file2	Rename or move file1 to file2,if file2 is an existing
		directory
21.	ln -s file link	Create symbolic link link to file
Process management
1.	ps	To display the currently working processes
2.	top	Display all running process

3.	kill pid	Kill the process with given pid
4.	killall proc	Kill all the process named proc
5.	pkill pattern	Will kill all processes matching the pattern
6.	bg	List stopped or background jobs,resume a stopped
		job in the background
7.	fg	Brings the most recent job to foreground
8.	fg n	Brings job n to the foreground

Searching

1.	grep pattern file	Search for pattern in file
2.	grep -r pattern dir	Search recursively for pattern in dir
3.	command | grep	Search pattern in the output of a command
	pa
4.	locate file	Find all instances of file
5.	find . -name filename	Searches in the current directory (represented by
		a period) and below it, for files and directories with
		names starting with filename
6.	pgrep pattern	Searches for all the named processes , that
		matches with the pattern and, by default, returns
		their ID

System Info

1.	date	Show the current date and time
2.	cal	Show this month's calender
3.	uptime	Show current uptime
4.	w	Display who is on line
5.	whoami	Who you are logged in as

6.	finger user	Display information about user
7.	uname -a	Show kernel information
8.	cat /proc/cpuinfo	Cpu information
9.	cat proc/meminfo	Memory information
10.	man command	Show the manual for command
11.	df	Show the disk usage
12.	du	Show directory space usage
13.	free	Show memory and swap usage
14.	whereis app	Show possible locations of app
15.	which app	Show which applications will be run by default

Compression

1.	tar cf file.tar file	Create tar named file.tar containing file
2.	tar xf file.tar	Extract the files from file.tar
3.	tar czf file.tar.gz files	Create a tar with Gzip compression
4.	tar xzf file.tar.gz	Extract a tar using Gzip
5.	tar cjf file.tar.bz2	Create tar with Bzip2 compression
6.	tar xjf file.tar.bz2	Extract a tar using Bzip2
7.	gzip file	Compresses file and renames it to file.gz
8.	gzip -d file.gz	Decompresses file.gz back to file

Network

1.	ping host	Ping host and output results
2.	whois domain	Get whois information for domains
3.	dig domain	Get DNS information for domain
4.	dig -x host	Reverse lookup host
5.	wget file	Download file
6.	wget -c file	Continue a stopped download

Shortcuts
1.	ctrl+c	Halts the current command
2.	ctrl+z	Stops the current command, resume with fg in the
		foreground or bg in the background
3.	ctrl+d	Logout the current session, similar to exit
4.	ctrl+w	Erases one word in the current line
5.	ctrl+u	Erases the whole line
6.	ctrl+r	Type to bring up a recent command
7.	!!	Repeats the last command
8.	exit	Logout the current session