need for a file system

• hardware

• file

  • size
  • type
  • authorization
  • read and write time

• operations

common file system:

• FAT(File Allocation Table)
  connect by points and write by order
• ext2(second extended file system)
  
  • supernode | file sysem descrip | inode bitmap | block bitmap | inode | block
    
  • use hashmap (inode) record file content
    
    • inode -> meta Data
      
    • block -> file content
      
  • use bitmap record whether it is empty
    
  • fixed size block: 1k, 2k, 4k
    
  • fixed size inode: 128byte
    
  • one inode has at least one block
    
  • use super node to record file system meta Data
    • the number of inode and block
      
    • the stat of bitmaps
      
    • the size of inode and block
      
    • start point of each part
      
  • larger size: indirect inode
    
• ext3 log file system: in order to check errors efficiently
  

linux

• group
  
  • owner
    
  • owners’ group
    
  • others
    
• drwxr-xr-x:
  
  • d refers dictonary; - refers file;
    
  • r readable : 4
    
  • w writable : 2
    
  • x executable : 1
    
  • r-x : 4 + 1 = 5
    
• commands:
  
  • find: find Desktop -name “.”
    
  • grep: grep “pattern” filename
  • pipe: find . -name “*.java” | xargs grep “public”
    (xargs: pass previous contect as argus for current command)
  • awk ‘{x+=$2+$3;a[NR]=$2+$3}END{y=x/NR;for(i in a){if(a[i] < y) z++} print z}’ table.txt