C Programming/POSIX Reference/sys/stat.h

<sys/stat.h> is the header in the C POSIX library for the C programming language that contains constructs that facilitate getting information about files attributes.

Member functions

Name	Notes
int stat (const char *filename, struct stat *buf)	The stat function returns information about the attributes of the file named by filename in the structure pointed to by buf. If filename is the name of a symbolic link, the attributes you get describe the file that the link points to. If the link points to a nonexistent file name, then stat fails reporting a nonexistent file. The return value is 0 if the operation is successful, or -1 on failure. When the sources are compiled with _FILE_OFFSET_BITS == 64 this function is in fact stat64 since the LFS interface transparently replaces the normal implementation. errno Errors: ENOENT means the file named by filename doesn't exist.
int stat64 (const char *filename, struct stat64 *buf)	This function is similar to stat but it is also able to work on files larger than 2^31 bytes on 32-bit systems. To be able to do this the result is stored in a variable of type struct stat64 to which buf must point. When the sources are compiled with _FILE_OFFSET_BITS == 64 this function is available under the name stat and so transparently replaces the interface for small files on 32-bit machines. errno Errors: ENOENT means the file named by filename doesn't exist.
int fstat (int filedes, struct stat *buf)	The fstat function is like stat, except that it takes an open file descriptor (filedes)as an argument instead of a file name. Like stat, fstat returns 0 on success and -1 on failure. When the sources are compiled with _FILE_OFFSET_BITS == 64 this function is in fact fstat64 since the LFS interface transparently replaces the normal implementation. errno Errors: EBADF means the filedes argument is nos a valid file descriptor.
int fstat64 (int filedes, struct stat64 *buf)	This function is similar to fstat but is able to work on large files on 32-bit platforms. For large files the file descriptor filedes should be obtained by open64 or creat64. The buf pointer points to a variable of type struct stat64 which is able to represent the larger values. When the sources are compiled with _FILE_OFFSET_BITS == 64 this function is available under the name fstat and so transparently replaces the interface for small files on 32-bit machines. errno Errors: EBADF means the filedes argument is nos a valid file descriptor.
int lstat (const char *filename, struct stat *buf)	The lstat function is like stat, except that it does not follow symbolic links. If filename is the name of a symbolic link, lstat returns information about the link itself; otherwise lstat works like stat. See Symbolic Links. When the sources are compiled with _FILE_OFFSET_BITS == 64 this function is in fact lstat64 since the LFS interface transparently replaces the normal implementation.
int lstat64 (const char *filename, struct stat64 *buf)	The lstat function is like stat, except that it does not follow symbolic links. If filename is the name of a symbolic link, lstat returns information about the link itself; otherwise lstat works like stat. See Symbolic Links. When the sources are compiled with _FILE_OFFSET_BITS == 64 this function is in fact lstat64 since the LFS interface transparently replaces the normal implementation.

Member constants

The following POSIX macros are defined to check the file type using the st_mode field:

Name	Notes
S_ISREG(m)	is it a regular file?
S_ISDIR(m)	is it a directory?
S_ISCHR(m)	is it a character device?
S_ISBLK(m)	is it a block device?
S_ISFIFO(m)	is it a FIFO (named pipe)?
S_ISLNK(m)	is it a symbolic link? (Not in POSIX.1-1996.)
S_ISSOCK(m)	is it a socket? (Not in POSIX.1-1996.)

The following flags are defined for the st_mode field:

Name	Value	Notes
S_IFMT	0170000	bit mask for the file type bit fields
S_IFSOCK	0140000	socket
S_IFLNK	0120000	symbolic link
S_IFREG	0100000	regular file
S_IFBLK	0060000	block device
S_IFDIR	0040000	directory
S_IFCHR	0020000	character device
S_IFIFO	0010000	FIFO
S_ISUID	0004000	set UID bit
S_ISGID	0002000	set-group-ID bit (see below)
S_ISVTX	0001000	sticky bit (see below)
S_IRWXU	00700	mask for file owner permissions
S_IRUSR	00400	owner has read permission
S_IWUSR	00200	owner has write permission
S_IXUSR	00100	owner has execute permission
S_IRWXG	00070	mask for group permissions
S_IRGRP	00040	group has read permission
S_IWGRP	00020	group has write permission
S_IXGRP	00010	group has execute permission
S_IRWXO	00007	mask for permissions for others (not in group)
S_IROTH	00004	others have read permission
S_IWOTH	00002	others have write permission
S_IXOTH	00001	others have execute permission

The set-group-ID bit (S_ISGID) has several special uses. For a directory it indicates that BSD semantics is to be used for that directory: files created there inherit their group ID from the directory, not from the effective group ID of the creating process, and directories created there will also get the S_ISGID bit set. For a file that does not have the group execution bit (S_IXGRP) set, the set-group-ID bit indicates mandatory file/record locking. The sticky bit (S_ISVTX) on a directory means that a file in that directory can be renamed or deleted only by the owner of the file, by the owner of the directory, and by a privileged process.

POSIX does not describe the S_IFMT, S_IFSOCK, S_IFLNK, S_IFREG, S_IFBLK, S_IFDIR, S_IFCHR, S_IFIFO, S_ISVTX bits, but instead demands the use of the macros S_ISDIR(), etc. The S_ISLNK() and S_ISSOCK() macros are not in POSIX.1-1996, but both are present in POSIX.1-2001; the former is from SVID 4, the latter from SUSv2.

Other Systems - Values that have been (or are) in use on various systems:

hex	name	ls	octal	description
f000	S_IFMT		170000	mask for file type
0000			000000	SCO out-of-service inode; BSD unknown type; SVID-v2 and XPG2 have both 0 and 0100000 for ordinary file
1000	S_IFIFO	p|	010000	FIFO (named pipe)
2000	S_IFCHR	c	020000	character special (V7)
3000	S_IFMPC		030000	multiplexed character special (V7)
4000	S_IFDIR	d/	040000	directory (V7)
5000	S_IFNAM		050000	XENIX named special file with two subtypes, distinguished by st_rdev values 1, 2
0001	S_INSEM	s	000001	XENIX semaphore subtype of IFNAM
0002	S_INSHD	m	000002	XENIX shared data subtype of IFNAM
6000	S_IFBLK	b	060000	block special (V7)
7000	S_IFMPB		070000	multiplexed block special (V7)
8000	S_IFREG	-	100000	regular (V7)
9000	S_IFCMP		110000	VxFS compressed
9000	S_IFNWK	n	110000	network special (HP-UX)
a000	S_IFLNK	l@	120000	symbolic link (BSD)
b000	S_IFSHAD		130000	Solaris shadow inode for ACL (not seen by userspace)
c000	S_IFSOCK	s=	140000	socket (BSD; also "S_IFSOC" on VxFS)
d000	S_IFDOOR	D>	150000	Solaris door
e000	S_IFWHT	w%	160000	BSD whiteout (not used for inode)
0200	S_ISVTX		001000	sticky bit: save swapped text even after use (V7) reserved (SVID-v2). On non-directories: don’t cache this file (SunOS). On directories: restricted deletion flag (SVID-v4.2)
0400	S_ISGID		002000	set-group-ID on execution (V7) for directories: use BSD semantics for propagation of GID
0400	S_ENFMT		002000	SysV file locking enforcement (shared with S_ISGID)
0800	S_ISUID		004000	set-user-ID on execution (V7)
0800	S_CDF		004000	directory is a context dependent file (HP-UX)

A sticky command appeared in Version 32V AT&T UNIX.

Member types

Data types defined in the <sys/stat.h> header include:

struct stat {
  dev_t     st_dev;     /* ID of device containing file */
  ino_t     st_ino;     /* inode number */
  mode_t    st_mode;    /* protection */
  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 file system I/O */
  blkcnt_t  st_blocks;  /* number of blocks allocated */
  time_t    st_atime;   /* time of last access */
  time_t    st_mtime;   /* time of last modification */
  time_t    st_ctime;   /* time of last status change */
};

Example

A short example of <sys/stat.h> usage is:

/**************************************************************
 abstract ls meaning
 **************************************************************/
#include <stdio.h>
#include <sys/stat.h>
#include <string.h>
#include <errno.h>
 
int            main(int argc, char **argv)
{
  struct stat  file_stat;
 
  while (argc-- > 1)
    {
      if (lstat(argv[argc], &file_stat) == -1)
        fprintf(stderr, "%s\n", strerror(errno));
      else
        {
          fprintf(stdout, "Links\tUid\tGid\tSize\tName\n");
          fprintf(stdout, "%u\t%u\t%u\t%u\t%s\n", file_stat.st_nlink,
                  file_stat.st_uid, file_stat.st_gid, file_stat.st_size,
                  argv[argc]);
        }
    }
  return 0;
}

Put the source in a file (main.c) and compile this:

 gcc main.c -o test

Now, to run type:

 ./test main.c
 ./test *

References

• Gnu File Attributes