小记——linux文件元属性

末蓝、 2022-09-23 13:59 139阅读 0赞

linux文件元属性是指文件的inode号、拥有者、大小、修改时间等属性，在linux中用以下结构体表示

<sys/stat.h>
    struct stat {
    dev_t st_dev; /* ID of device containing file */
    ino_t st_ino; /* inode number */
    mode_t st_mode; /* permissions */
    nlink_t st_nlink; /* number of hard links */
    uid_t st_uid; /* user ID of owner */
    gid_t st_gid; /* group ID of owner */
    dev_t st_rdev; /* device ID (if special file) */
    off_t st_size; /* total size in bytes */
    blksize_t st_blksize; /* blocksize for filesystem I/O */
    blkcnt_t st_blocks; /* number of blocks allocated */
    time_t st_atime; /* last access time */
    time_t st_mtime; /* last modification time */
    time_t st_ctime; /* last status change time */
    };

1.  获取文件属性

#include <sys/types.h>
    #include <sys/stat.h>
    #include <unistd.h>
    int stat (const char *path, struct stat *buf);
    int fstat (int fd, struct stat *buf);
    int lstat (const char *path, struct stat *buf);

其中lstat函数是用一获取符号链接的属性

==>例程：获取文件的大小

==>例程：获取文件的类型

#include <sys/types.h>
    #include <sys/stat.h>
    #include <unistd.h>
    #include <stdio.h>
    int main (int argc, char *argv[])
    {
    struct stat sb;
    int ret;
    if (argc < 2) {
    fprintf (stderr,
    "usage: %s <file>\n", argv[0]);
    return 1;
    }
    ret = stat (argv[1], &sb);
    if (ret) {
    perror ("stat");
    return 1;
    }
    printf ("File type: ");
    switch (sb.st_mode & S_IFMT) {
    case S_IFBLK:
    printf("block device node\n");
    break;
    case S_IFCHR:
    printf("character device node\n");
    break;
    case S_IFDIR:
    printf("directory\n");
    break;
    case S_IFIFO:
    printf("FIFO\n");
    break;
    case S_IFLNK:
    printf("symbolic link\n");
    break;
    case S_IFREG:
    printf("regular file\n");
    break;
    case S_IFSOCK:
    printf("socket\n");
    break;
    default:
    printf("unknown\n");
    break;
    }
    return 0;
    }

其中sb.st\_mode & S\_IFMT运算是用于消除无干位的数据，得到真实的文件类型。

2. 修改权限

#include <sys/types.h>
    #include <sys/stat.h>
    int chmod (const char *path, mode_t mode);
    int fchmod (int fd, mode_t mode);

==>例程：修改文件权限

int ret;
    /*
    * Set 'map.png' in the current directory to
    * owner-readable and -writable. This is the
    * same as 'chmod 600 ./map.png'.
    */
    ret = chmod ("./map.png", S_IRUSR | S_IWUSR);
    if (ret)
    perror ("chmod");

3. 修改所有者与所有组

#include <sys/types.h>
    #include <unistd.h>
    int chown (const char *path, uid_t owner, gid_t group);
    int lchown (const char *path, uid_t owner, gid_t group);
    int fchown (int fd, uid_t owner, gid_t group);

==>例程：修改文件所有组

struct group *gr;
    int ret;
    /*
    * getgrnam() returns information on a group
    * given its name.
    */
    gr = getgrnam ("officers");
    if (!gr) {
    /* likely an invalid group */
    perror ("getgrnam");
    return 1;
    }
    /* set manifest.txt's group to 'officers' */
    ret = chown("manifest.txt", -1, gr->gr_gid);
    if (ret)
    perror ("chown");

==>例程：修改文件为root用户所有

/*
    * make_root_owner - changes the owner and group of the file
    * given by 'fd' to root. Returns 0 on success and −1 on
    * failure.
    */
    int make_root_owner (int fd)
    {
    int ret;
    /* 0 is both the gid and the uid for root */
    ret = fchown (fd, 0, 0);
    if (ret)
    perror ("fchown");
    return ret;
    }

其他注意内容：扩展属性