Linux file system

1. Standard directory structure

• / - the topmost
• /dev - all the devices are accessible as files
• /var - "variable" data such as mails, log files, databases
• /usr - almost all the packages installed
• /etc - con?guration files
• /home - home directories for all the users
• /root - home directory of the privileged user root
• /mnt - used to mount other directories/partitions

2. File Attributes

• To see the file attributes type ls -l on your terminal

ls -l

total 156-rw-r--r--  1 root root   1053 Sep 22  2010 anaconda-ks.cfg-rw-r--r--  1 root root 127004 Sep 22  2010 CHECKSUMSdrwxr-xr-x  2 root root   4096 Aug  3 00:02 Desktop-rw-r--r--  1 root root    100 Jun  6 22:14 svn-checkout-command

•  It has 10 characters, first character is d if its directory and - if its file.
• Next 9 characters are divided into three groups with a set of 3 characters each
• First 3 characters - Owner of the file or directory
• Next 3 characters - Group
• Last 3 characters - Others
• r - Read i.e. File or directory is readable
• w - Write i.e. File or directory is writable
• x - Execute i.e. File or directory is executable
• -rw-r–r– means it has read, write but not execute permissions for the owner of the file, only read permissions for the group and only read permissions for others.
• The third column of the command ls -l tells about the owner of the file, next column tells to which group it belongs

3. Changing the File attributes

chmod Changing the permissions of the file

Usage: 

$ chmod o+x Testing.java

$ chmod 655 Testing.java

4. Changing ownership

chown command is used for changing the ownership and also group of the file

Usage:

$ chown guest Testing.java

$ chown guest:guest Testing.java

5. File system commands

• Deleting Files - rm
• Copying and moving files - cp, mv
• Creating directories - mkdir
• Deleting Empty Directory - rmdir

$ rm Testing.java

//deletes the file Testing.java

$ cp Testing.java Copy.java

//creates the copy of Testing.java

$ mv Testing.java Test.java

//renames the file Testing.java to Test.java

$ mkdir newDir

//Creates directory newDir

$ rmdir newDir

//deletes directory newDir newDir should be empty.