Linux System Programming with C118

Linux is a popular open-source operating system that provides a wide range of features and capabilities. System programming is the process of writing programs that interact directly with the operating system kernel. This type of programming is essential for developing device drivers, operating system extensions, and other low-level software.

C is a powerful and versatile programming language that is well-suited for system programming. It provides low-level access to the operating system and hardware, and it allows programmers to write efficient and portable code. In this tutorial, we will explore the basics of Linux system programming with C.

Getting Started

To get started with Linux system programming, you will need a C compiler and a Linux operating system. You can download a free C compiler such as GCC from the GNU website. Once you have installed the compiler, you can create a new C program file with the following command:```
touch hello.c
```

You can then open the file in a text editor and add the following code:```c
#include
int main() {
printf("Hello, world!");
return 0;
}
```

This program simply prints the message "Hello, world!" to the console. To compile the program, you can use the following command:```
gcc hello.c -o hello
```

This will create an executable file named "hello". You can then run the program by typing the following command:```
./hello
```

This will print the message "Hello, world!" to the console.

System Calls

System calls are the interface between user programs and the operating system kernel. They allow programs to request services from the kernel, such as reading and writing files, creating and managing processes, and accessing hardware devices. System calls are typically invoked using the `syscall()` function. The following code shows how to use the `syscall()` function to print the message "Hello, world!" to the console:```c
#include
#include
int main() {
syscall(SYS_write, 1, "Hello, world!", 13);
return 0;
}
```

In this example, the `syscall()` function is used to invoke the `SYS_write` system call. The first argument to the `syscall()` function is the system call number. The second argument is the file descriptor for the console. The third argument is a pointer to the message to be printed. The fourth argument is the length of the message.

File I/O

File I/O is a fundamental part of system programming. The following code shows how to open a file, read its contents, and write to it:```c
#include
#include
int main() {
FILE *fp = fopen("", "r");
if (fp == NULL) {
perror("fopen");
exit(EXIT_FAILURE);
}
char buffer[1024];
while (fgets(buffer, sizeof(buffer), fp) != NULL) {
printf("%s", buffer);
}
fclose(fp);
fp = fopen("", "w");
if (fp == NULL) {
perror("fopen");
exit(EXIT_FAILURE);
}
fprintf(fp, "Hello, world!");
fclose(fp);
return 0;
}
```

In this example, the `fopen()` function is used to open the file "" for reading. The `fgets()` function is then used to read the contents of the file into a buffer. The `printf()` function is used to print the contents of the buffer to the console. The `fclose()` function is used to close the file.

The `fopen()` function can also be used to open a file for writing. The following code shows how to open a file for writing and write to it:```c
#include
#include
int main() {
FILE *fp = fopen("", "w");
if (fp == NULL) {
perror("fopen");
exit(EXIT_FAILURE);
}
fprintf(fp, "Hello, world!");
fclose(fp);
return 0;
}
```

In this example, the `fopen()` function is used to open the file "" for writing. The `fprintf()` function is then used to write the message "Hello, world!" to the file. The `fclose()` function is used to close the file.

Processes and Threads

Processes and threads are two fundamental concepts in system programming. Processes are independent units of execution, while threads are lightweight processes that share the same memory space. The following code shows how to create a new process:```c
#include
#include
#include
int main() {
pid_t pid = fork();
if (pid == 0) {
printf("Child process");
} else if (pid > 0) {
printf("Parent process");
}
return 0;
}
```

In this example, the `fork()` function is used to create a new process. The `pid` variable stores the process ID of the new process. The `printf()` function is used to print a message to the console. The `if` statement is used to determine whether the current process is the parent process or the child process.

The following code shows how to create a new thread:```c
#include
#include
#include
void *thread_function(void *arg) {
printf("Thread function");
return NULL;
}
int main() {
pthread_t thread;
pthread_create(&thread, NULL, thread_function, NULL);
pthread_join(thread, NULL);
return 0;
}
```

In this example, the `pthread_create()` function is used to create a new thread. The `thread_function()` function is the function that will be executed by the new thread. The `pthread_join()` function is used to wait for the new thread to finish executing.

Conclusion

This tutorial has provided a basic introduction to Linux system programming with C. We have covered topics such as system calls, file I/O, processes, and threads. This knowledge will serve as a foundation for further exploration of the Linux operating system and system programming in general.

2024-12-08

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