Files and File System Structure

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Chapter 7

• Files and File System Structure

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Files under LINUX

• File a sequence of bytes
• All files, I/O devices, and interfaces are
  treated as files
• Directories are also files (Files containing list
  of files within them)

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LINUX File Types

• Simple/Ordinary file
• Directory
• Symbolic (soft) link
• Special File (device)
• Character special
• Block special
• Named Pipe (FIFO)

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Filenames

• Linux does not attach any particular meaning to
  any file
• Application programs determine how to use files
• Some applications require certain extensions, but
  LINUX does not use any standard convention for
  file extensions
• Linux file names can be up to 255 characters
  (including any extension and the . before it)
• It is permitted but generally unwise to embed
  special or invisible characters in file names

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Table 7.1 Commonly Used Extensions
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Figure 7.2  A typical LINUX file system structure
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Table 7.2 Main Subdirectories in /usr
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Table 7.2 Main Subdirectories in /usr
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Table 7.3 Some Important Hidden Files and Their
Purposes
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Table 7.4 Summary of the Output of the ls -l
Command
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Figure 7.1  Structure of a directory entry
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Figure 7.5  Contents of an inode
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Inode Structure

• / Inode table. This table holds inodes that are
  currently in use. In some cases they have been
  opened by an open() or creat() system call, in
  other cases the file system itself needs the
  inode for one reason or another, such as to
  search a directory for a path name. The first
  part of the struct holds fields that are present
  on the disk the second part holds fields not
  present on the disk. The disk inode part is also
  declared in "type.h" as 'd1_inode' for V1 file
  systems and 'd2_inode' for V2 file systems. /
• EXTERN struct inode
• mode_t i_mode / file type,
  protection, etc.
• nlink_t i_nlinks / how many links
  to this file
• uid_t i_uid / user id of the file's owner
• gid_t i_gid / group number
• off_t i_size / current file size in bytes
• time_t i_atime / time of last access (V2
  only)
• time_t i_mtime / when was file data last
  changed
• time_t i_ctime / when was inode itself
  changed (V2 only)
• zone_t i_zoneV2_NR_TZONES / zone
  numbers for direct, ind, and dbl ind /

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Figure 7.6  Logical view of a disk drive(an
array of disk blocks)
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Figure 7.7  Relationship between the file lab1.c
in a directory and its contents on disk
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Figure 7.8  Relationship between a file
descriptor and contents of the file on disk
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Figure 7.9  Relationship of a file descriptor and
the corresponding file