IO interview questions

Written interview questions ：

1 file IO And standards IO The difference between

file IO yes Linux system call （ kernel API）, And the standard IO yes C Library functions ;

file IO Without buffer , standard IO With buffer

file IO The operation is the file descriptor , standard IO The operation is the flow FILE

file IO And standards IO The function names used are different

2 What is flow ？、 How do you understand standards IO Flow in

        The process of input and output .

             The flow of data , Data has no boundaries   Linux The operation on a stream is called IO operation 

3 What is a file descriptor 、 Principles for using file descriptors 、 What is the maximum size of a file descriptor

ulimit –n

① Is a way to access files ② The principle of minimum distribution is generally followed ③ Used to identify the file accessed by the running program

4 What is an empty file 、 How an empty file is formed ？

      An empty file is an empty file ,

5 standard IO Access to files in r,r+,w,w+,a,a+ What do you mean

6 standard IO Medium r+ Corresponding documents IO What is the way to write ？

7、 Pen test ： What's the difference between a process and a program

1 The program is static , Storage immovable ; The process is dynamic , It's a running program

2 The program is on disk , The process runs in memory

3 process = Program + PCB（ Process control block ）+ Time slice

8、 What is write time replication technology ？

    Use vfork Function to create a new child process , But it will share the address space with the parent process , When the new child process executes different code data from the parent process , Only then will the memory be copied , Create a new space , This technology becomes ” When writing copy ”-Copy on write

9、vfork What are the execution characteristics of ？

10、 fork And vfork What's the difference ？

vfork Share address space with parent process 、fork Is to open up a new address space

vfork Make it clear that the subprocess executes first

11、 fork What content of the parent process is copied by the child process ？

 The user no. UIDs And user group number GIDs

 Environmental Science Environment

 Stack 

Shared memory
Open the descriptor of the file
Close on execution (Close-on-exec) sign
The signal (Signal) Control settings
Process group number
Current working directory
root directory
Create screen word in file mode
Resource constraints
Control terminal

  The child process is created , The processor allocates memory for subprocesses , Code snippet of the parent process , Data segment , The stack segment is copied to the child process 

12、 Interview questions ：exit Functions and _exit The difference in the use of functions

    difference ：_exit It's a system call ,exit It's a library call 

  exit Will clean up IO cache ,_exit It's a direct exit , Cache will not be cleaned up 

13、

What is the child process that does not copy the parent process ？（ What are unique to child processes 、 What are the child processes different from the parent process ）？

14、 Please write out the process of creating a daemon

Pen test ：

Face to face examination questions ： What is Daemons ？

Which resources of the process are shared by threads ？

Which resources of a process cannot be accessed by a thread ？

2 Which resources of the process are shared by threads ？

• Executable instructions

• Static data , Global data

• File descriptor opened in process

• Signal processing functions

• Current working directory

• user ID

• User group ID

3 Resources owned independently by threads ？

       Threads ID (TID)

PC( Program counter ) And related registers

Stack

• local variable

• The return address

Error number (errno)

Signal mask and priority

Execution status and properties

Interview questions ：

 Why should the corresponding read and write ends be closed in the respective processes when the anonymous pipes are used ？

 1  To achieve half duplex 

 2  In order to avoid programmer misoperation 

Interview questions ： What should be paid attention to when using pipeline files ？

If there is more than one write , A read , Write first and then read , The read content is the last written content .

If there is more than one write , A read , Read first and then write , The read content is the content written at the beginning .

If it is a write , Multiple reading . Write first and then read , Start the process to read first .

If it is a write , Multiple reading . Read first and then write , After starting the reading process, the content is read , Start the reading process to read the subsequent contents , If the post read process finishes reading the contents written , Then the read result of the later started process is 0

Pen test ： Please describe in detail OSI Seven layer model ？

     Please explain OSI The seven story model and TCP/IP The difference between the four layer model ？