📚 README

🔌 Complete a shell program with "manual" handling of pipes

This program that collects messages from multiple programs and displays them on the screen. Use a named pipe for communication. 💡 Hint: Create an rdfifo program whose task is to create a FIFO queue and read data from it.

❓ FAQ:

Question	Answer
How will you pass the common name of the FIFO queue to these programs?	Through a static variable
How to ensure that the program collecting messages works even when there is no program writing to the link?	Through an infinite loop process with sleep
How to ensure that messages from different programs are displayed in full, i.e., not separated by messages from other programs?	flush? (to be verified)

📤 Output sample

[23:30:20](pid 17400) DEBUG: Passed rdfifo 73 - while1

karol@carlo:~/eclipse-workspaces/unx_sys_programming/Debug$ ./unx_sys_programming -w

Input option value=(null) set program to write to FIFO

[23:30:20](pid 17411) DEBUG: Passed wrfifo 148 : mkfifo exist: 17
[23:30:20](pid 17411) DEBUG: Passed wrfifo 157 - pipe opened to read-write
[23:30:20](pid 17400) DEBUG: Passed rdfifo 104 - Remove FIFO
[23:30:20](pid 17411) DEBUG: Passed wrfifo 174 : client succesed write to pipe: #0 test PID: 17411: text -> Thu Jan 28 23:36:02 2016
[23:30:20](pid 17400) DEBUG: Passed rdfifo 107 : reader reads record: #0 test PID: 17411: text -> Thu Jan 28 23:36:02 2016
[23:30:20](pid 17411) DEBUG: Passed wrfifo 174 : client succesed write to pipe: #1 test PID: 17411: text -> Thu Jan 28 23:36:03 2016
[23:30:20](pid 17400) DEBUG: Passed rdfifo 107 : reader reads record: #1 test PID: 17411: text -> Thu Jan 28 23:36:03 2016
[23:30:20](pid 17411) DEBUG: Passed wrfifo 174 : client succesed write to pipe: #2 test PID: 17411: text -> Thu Jan 28 23:36:04 2016
[23:30:20](pid 17400) DEBUG: Passed rdfifo 107 : reader reads record: #2 test PID: 17411: text -> Thu Jan 28 23:36:04 2016
[23:30:20](pid 17411) DEBUG: Passed wrfifo 174 : client succesed write to pipe: #3 test PID: 17411: text -> Thu Jan 28 23:36:05 2016
[23:30:20](pid 17400) DEBUG: Passed rdfifo 107 : reader reads record: #3 test PID: 17411: text -> Thu Jan 28 23:36:05 2016
[23:30:20](pid 17411) DEBUG: Passed wrfifo 174 : client succesed write to pipe: #4 test PID: 17411: text -> Thu Jan 28 23:36:06 2016
[23:30:20](pid 17400) DEBUG: Passed rdfifo 107 : reader reads record: #4 test PID: 17411: text -> Thu Jan 28 23:36:06 2016
[23:30:20](pid 17411) DEBUG: Passed wrfifo 174 : client succesed write to pipe: #5 test PID: 17411: text -> Thu Jan 28 23:36:07 2016
[23:30:20](pid 17400) DEBUG: Passed rdfifo 107 : reader reads record: #5 test PID: 17411: text -> Thu Jan 28 23:36:07 2016
[23:30:20](pid 17411) DEBUG: Passed wrfifo 174 : client succesed write to pipe: #6 test PID: 17411: text -> Thu Jan 28 23:36:08 2016
[23:30:20](pid 17400) DEBUG: Passed rdfifo 107 : reader reads record: #6 test PID: 17411: text -> Thu Jan 28 23:36:08 2016
[23:30:20](pid 17411) DEBUG: Passed wrfifo 174 : client succesed write to pipe: #7 test PID: 17411: text -> Thu Jan 28 23:36:09 2016
[23:30:20](pid 17400) DEBUG: Passed rdfifo 107 : reader reads record: #7 test PID: 17411: text -> Thu Jan 28 23:36:09 2016
[23:30:20](pid 17411) DEBUG: Passed wrfifo 174 : client succesed write to pipe: #8 test PID: 17411: text -> Thu Jan 28 23:36:10 2016
[23:30:20](pid 17400) DEBUG: Passed rdfifo 107 : reader reads record: #8 test PID: 17411: text -> Thu Jan 28 23:36:10 2016
[23:30:20](pid 17411) DEBUG: Passed wrfifo 174 : client succesed write to pipe: #9 test PID: 17411: text -> Thu Jan 28 23:36:11 2016
[23:30:20](pid 17400) DEBUG: Passed rdfifo 107 : reader reads record: #9 test PID: 17411: text -> Thu Jan 28 23:36:11 2016
[23:30:20](pid 17411) DEBUG: Passed wrfifo 180 - close fd
[23:30:20](pid 17400) DEBUG: Passed rdfifo 112 - EOF reader

[10]   Done                    ./unx_sys_programming -r

bash:~/eclipse-workspaces/unx_sys_programming/Debug$ ./unx_sys_programming -h

FIFO Program
A program without arguments creates a named pipe and writes data to it in a child process.
The program can be called with arguments so it works as read (r) from pipe or write to pipe (w).
A counter, PID and current time are written to the pipe.

Usage: ./unx_sys_programming [-r] [-w]

🚀 Usage example

Basic usage:

./unx_sys_programming

Or use with multiple processes:

./unx_sys_programming -r
./unx_sys_programming -w
./unx_sys_programming -w
./unx_sys_programming -w

🔀 Fork read environment - Tasks

Task Definitions

• z1: 📝 Write a program that shows which attributes of the parent process are inherited by the child process started with the fork() function, and which receive new values.

• z2: 📝 Write a program that shows which process attributes are preserved after the exec() function is executed.

• z3: 📝 Write a program that displays the process identifier (PID) and the name of the associated command for all processes started by the user specified in the program's call line.

💡 Hint: This information can be obtained by browsing the /proc directory from files (we are interested in directories whose owner is the given user) and the /proc/PID/status files

📋 Process Attributes

Each process is characterized by certain attributes:

Attribute	Description
🆔 PID	Process identifier
👨‍👩‍👧 PPID	Parent process identifier
👤 Real UID	Real user identifier of the process owner
👥 Real GID	Real process group identifier
⚡ Effective UID	Effective user identifier of the process owner
⚡ Effective GID	Effective process group identifier
📂 Directories	Current directory and root directory
🔐 File mask	File creation mask
🔌 Session ID	Session identifier
💻 Terminal	Controlling terminal
📁 File descriptors	Descriptors of open files
📢 Signal handling	Signal handling settings
🌍 Environment	Environment variable settings
💾 Resources	Resource limits

🧬 Process Inheritance & Differences

Inherited Properties

The child process inherits many properties from the parent process:

• Real user identifier, real group identifier
• Effective user identifier, effective group identifier
• Additional group identifiers
• Session identifier, controlling terminal
• User ID set signal and group ID set signal
• Open file descriptors (they are copied)
• Current working directory, root directory
• File creation mask, signal mask and signal handling dispositions
• Close-on-exec flag for all open file descriptors
• Environment, attached shared memory segments
• System resource limits

Key Differences

However, there are certain differences between the parent and child processes:

1. Return value from fork() - different in parent vs child
2. Process identifiers - each process gets a unique PID
3. Parent process identifiers - in the child process this is the parent's PID; in the parent process the PPID doesn't change
4. Timing values - in the child process, tms_utime, tms_cutime and tms_ustime are equal to 0
5. File locks - the child does not inherit file locks established in the parent process
6. Pending alarms - in the child process, all pending alarms are zeroed
7. Pending signals - in the child process, the set of pending signals is zeroed