Some information on this page is taken from here (German).

Process Control Block (PCB)

Contains the information about a process.

• C struct task_struct
• Pointer to code section (text)
• Pointer to data section
• State: running, ready, blocked, terminated
• Instruction pointer (IP): next instruction to execute
• Saved registers
• Memory information: pages
• Scheduler information
  • Priority
  • Pointer to scheduler queue
• Table with open file descriptors hold by this process

File Table

• 1 entry for each open file
• different processes can point to the same entry
• Entry:
  • number of i-nodes
  • position pointer
  • mode (read, write, append…)
  • pointer to v-node table

v-node Table

• i-node information
  • copied to v-node table when file is opened
  • owner
  • rights
  • user/group ids
  • number of links
• file information
• file size
• functions (file system dependent)

File Descriptors

File descriptors are unique ID’s (ints) that identify an open file.

3 descriptors are reserved by the system in <unistd.h>:

The number can differ but the given ones are common.

Functions that return a file descriptor (e.g. open(...)or creat(...)) return -1 if en error occurred.

File Types

There are 6 different file types in Linux:

• Regular files
• Directories
• Device files
• Sockets
• Pipes (named Pipes and FIFOs)
• Links (Soft- and Hardlinks)

Special Device Files

See here for a description for device files.