CS131 Week 5 and Week 6

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Questions and Answers

Which file descriptor represents the standard input in a process?

0 (correct)

Which file descriptor represents the standard output in a process?

1 (correct)

Which file descriptor represents the standard error in a process?

2 (correct)

What is the purpose of file descriptor 2?

Report errors Signup and view all the answers

Which one of these is NOT a UNIX shell?

Windows Shell Signup and view all the answers

What does the 'ps aux' command in UNIX do?

Displays all processes Signup and view all the answers

What does the exit code 0 typically indicate in UNIX?

Success Signup and view all the answers

What does the top command in UNIX do?

Shows process states Signup and view all the answers

Which program usually has a process ID of 0?

/etc/init Signup and view all the answers

What is the purpose of the 'login' program?

To compare encrypted results Signup and view all the answers

What is the function of 'getty' or 'sshd' program?

To manage physical or virtual terminals Signup and view all the answers

Which command is used to create a named pipe in Unix?

mkfifo Signup and view all the answers

What is the purpose of a socket in inter-process communication (IPC)?

To read and write data Signup and view all the answers

How are sockets and pipes related in the UNIX kernel?

Sockets are an extension of pipes Signup and view all the answers

Which of the following is an example of a filter command in UNIX?

cat Signup and view all the answers

What is the purpose of /dev/null in UNIX?

To ignore some output Signup and view all the answers

Which of the following is true about interprocess communication (IPC)?

IPC refers to communication between processes Signup and view all the answers

What is the purpose of pipes in UNIX?

To communicate between processes Signup and view all the answers

Which command is used to count the number of lines, words, and characters in a list of files and directories?

wc Signup and view all the answers

What is the purpose of a pipe in a command pipeline?

To connect the standard output of one program to the standard input of the next program Signup and view all the answers

Why is it beneficial to use pipes in a command pipeline instead of writing intermediate results to temporary files?

Programs can produce lots of I/O, so it's better to run them concurrently rather than wait for one to finish before starting the next one Signup and view all the answers

What is the purpose of the tee command in a command pipeline?

To duplicate an input character stream and send one copy to a file and write the other to standard output Signup and view all the answers

Study Notes

File Descriptors in UNIX

Standard input is represented by file descriptor 0.
Standard output is represented by file descriptor 1.
Standard error is represented by file descriptor 2.
File descriptor 2 (standard error) is used for sending error messages and diagnostics.

UNIX Shells

Not all command-line interfaces qualify as UNIX shells; examples of non-UNIX shells should be recognized.

Command Functions in UNIX

The 'ps aux' command displays information about all running processes, including user, PID, CPU, and memory usage.
An exit code of 0 typically indicates successful completion of a command or program.
The 'top' command provides a dynamic, real-time view of system processes, including resource usage metrics.

Process Identifications

The program with a process ID of 0 is usually the scheduler (also known as the idle process).
The 'login' program's purpose is to authenticate users and start a user session.

Programs for Terminal Management

The 'getty' program manages terminal sessions, providing login prompts.
The 'sshd' program allows secure remote access through the SSH protocol.

Named Pipes and Inter-process Communication

The command used to create a named pipe in UNIX is mkfifo.
Sockets facilitate inter-process communication (IPC) by enabling data exchange between processes, often over a network.
Sockets and pipes are both mechanisms for IPC in the UNIX kernel, allowing processes to communicate data.

Filter Commands and Interprocess Communication

An example of a filter command in UNIX includes commands like grep or awk, which process data streams.
The /dev/null device in UNIX acts as a data sink that discards any data written to it.

IPC and Its Functions

Interprocess communication (IPC) allows processes to share data, synchronize their actions, and manage concurrent execution.
Pipes are used in UNIX to facilitate data flow between processes, allowing the output of one command to serve as input for another.

File and Line Counting

The command wc is used to count lines, words, and characters in files and directories.

Command Pipelining

Pipes in a command pipeline enable efficient data transfer between commands without the need for temporary files, saving both time and system resources.
The tee command in a command pipeline duplicates input, allowing the data to be sent to both a file and the standard output simultaneously.

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Description

Understanding Redirection in Linux: Test your knowledge on using /dev/null and redirecting output