CS456 - Systems Programming Spring 2026

Displaying ./code/feb26/stat.c

/*

gives information about a specified file

> man 2 stat - to view general information about this system call
> man 3 stat - to view the stat structure itself 

there are a few variants of stat, only difference between them is what type of argument it takes
- stat : takes pathname from argv
- fstat: takes a file descriptor (from open system call) 
- lstat: same as stat, but if pathname is a symbolic link, it returns information about the link 
         itself, not the file it refers to.




*/

#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

int main(int argc, char **argv){

	if(argc < 2){
		fprintf(stderr, "Usage %s file\n", argv[0]);
		exit(1);
	}

	int fd;

	fd = open(argv[1], O_RDONLY); //using open system call

	if(fd == -1){
		fprintf(stderr, "ERROR: Cannot open %s, file probably does not exist.\n", argv[1]);
		exit(-1);
	}

	struct stat st;
	fstat(fd, &st); //since we have a file descriptor, we'll use the fstat variant
			//we wont be able to get info on links themselves unless we use lstat

	printf("Device: %ld\n", st.st_dev); // the device where the file resides 
	
	printf("Inode: %lu\n", st.st_ino);  // inode number, a unique integer identifier assigned to 
	                                    // every file or directory within a specific Linux/UNIX 
					    // filesystem
	
	printf("Mode: %o\n", st.st_mode);  // file mode, contains the type of file (regular, directory, 
	                                   // link) as well as the file permissions. generally 
					   // represented in octal.  

	printf("Number of Hard Links: %ld\n", st.st_nlink); // number of hard links to the file
	
	printf("User ID of Owner: %d\n", st.st_uid); //user ID of the owner of the file  

	printf("Group ID of Owner: %d\n", st.st_gid); //group ID of the owner of the file

	printf("Device ID (if special file): %ld\n", st.st_rdev); 
		// used if this file represents a device (like something in /dev)

	printf("File Size: %ld\n", st.st_size); //size of file in bytes

	printf("Blocksize for filesystem I/O: %ld\n", st.st_blksize); // number of blocks allocated to file, 
							              // usually in 512-byte units 

	//these values come from the timespec struct 
	// read "man timespec" for more info
	// st values come from define statements within stat struct
	printf("Last Access: %ld\n", st.st_atime);  // time of last access
	printf("Last Modified: %ld\n", st.st_mtime); // last modification
	printf("Last Status Change: %ld\n", st.st_ctime);  // time of last change to inode

	//more info can be found in man 7 inode 

	close(fd);

	return 0;

}