stat

stat, fstat, lstat - get file status

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

These functions return information about a file. No permissions are required on the file itself, but in the case of R stat () and R lstat () execute (search) permission is required on all of the directories in path that lead to the file.

R stat () stats the file pointed to by path and fills in R buf . R lstat () is identical to R stat (), except that if path is a symbolic link, then the link itself is stat-ed, not the file that it refers to. R fstat () is identical to R stat (), except that the file to be stat-ed is specified by the file descriptor R filedes .

All of these system calls return a stat structure, which contains the following fields:

The st_dev field describes the device on which this file resides. The st_rdev field describes the device that this file (inode) represents. The st_size field gives the size of the file (if it is a regular file or a symbolic link) in bytes. The size of a symlink is the length of the pathname it contains, without a trailing null byte. The st_blocks field indicates the number of blocks allocated to the file, 512-byte units. (This may be smaller than R st_size /512, for example, when the file has holes.) The R st_blksize field gives the "preferred" blocksize for efficient file system I/O. (Writing to a file in smaller chunks may cause an inefficient read-modify-rewrite.)

Not all of the Linux filesystems implement all of the time fields. Some file system types allow mounting in such a way that file accesses do not cause an update of the st_atime field. (See `noatime' in mount(8).) The field st_atime is changed by file accesses, for example, by execve(2), mknod(2), pipe(2), utime(2) and read(2) (of more than zero bytes). Other routines, like mmap(2), may or may not update R st_atime . The field st_mtime is changed by file modifications, for example, by mknod(2), truncate(2), utime(2) and write(2) (of more than zero bytes). Moreover, st_mtime of a directory is changed by the creation or deletion of files in that directory. The st_mtime field is not changed for changes in owner, group, hard link count, or mode. The field st_ctime is changed by writing or by setting inode information (i.e., owner, group, link count, mode, etc.).

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

R S_ISREG (m)

R S_ISDIR (m)

R S_ISCHR (m)

R S_ISBLK (m)

R S_ISFIFO (m)

R S_ISLNK (m)

R S_ISSOCK (m)

The following flags are defined for the st_mode field:

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.

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

EACCES

EBADF

EFAULT

ELOOP

ENAMETOOLONG

ENOENT

ENOMEM

ENOTDIR

These system calls conform to SVr4, 4.3BSD, POSIX.1-2001. Use of the st_blocks and st_blksize fields may be less portable. (They were introduced in BSD. The interpretation differs between systems, and possibly on a single system when NFS mounts are involved.)

POSIX does not describe the R S_IFMT , R S_IFSOCK , R S_IFLNK , R S_IFREG , R S_IFBLK , R S_IFDIR , R S_IFCHR , R S_IFIFO , R S_ISVTX bits, but instead demands the use of the macros R S_ISDIR (), etc. The R S_ISLNK () and R 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.

Unix V7 (and later systems) had R S_IREAD , R S_IWRITE , R S_IEXEC , where POSIX prescribes the synonyms R S_IRUSR , R S_IWUSR , R S_IXUSR .

Other Systems

Values that have been (or are) in use on various systems: l l l l l. 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.

Linux Notes

Since kernel 2.5.48, the stat structure supports nanosecond resolution for the three file timestamp fields. Glibc exposes the nanosecond component of each field using names either of the form R st_atim.tv_nsec , if the _BSD_SOURCE or _SVID_SOURCE feature test macro is defined, or of the form R st_atimensec , if neither of these macros is defined. On file systems that do not support sub-second timestamps, these nanosecond fields are returned with the value 0. For most files under the /proc directory, R stat () does not return the file size in the st_size field; instead the field is returned with the value 0.

The following program calls stat(2) and displays selected fields in the returned stat structure.

#include <sys/types.h>
#include <sys/stat.h>
#include <time.h>
#include <stdio.h>
#include <stdlib.h>

int
main(int argc, char *argv[])
{
    struct stat sb;

    if (argc != 2) {
        fprintf(stderr, "Usage: %s <pathname>\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    if (stat(argv[1], &sb) == -1) {
        perror("stat");
        exit(EXIT_SUCCESS);
    }

    printf("File type:                ");
    switch (sb.st_mode & S_IFMT) {
    case S_IFBLK:  printf("block device\n");            break;
    case S_IFCHR:  printf("character device\n");        break;
    case S_IFDIR:  printf("directory\n");               break;
    case S_IFIFO:  printf("FIFO/pipe\n");               break;
    case S_IFLNK:  printf("symlink\n");                 break;
    case S_IFREG:  printf("regular file\n");            break;
    case S_IFSOCK: printf("socket\n");                  break;
    default:       printf("unknown?\n");                break;
    }

    printf("I-node number:            %ld\n", (long) sb.st_ino);

    printf("Mode:                     %lo (octal)\n",
            (unsigned long) sb.st_mode);

    printf("Link count:               %ld\n", (long) sb.st_nlink);
    printf("Ownership:                UID=%ld   GID=%ld\n",
            (long) sb.st_uid, (long) sb.st_gid);

    printf("Preferred I/O block size: %ld bytes\n",
            (long) sb.st_blksize);
    printf("File size:                %lld bytes\n",
            (long long) sb.st_size);
    printf("Blocks allocated:         %lld\n",
            (long long) sb.st_blocks);

    printf("Last inode change:        %s", ctime(&sb.st_ctime));
    printf("Last file access:         %s", ctime(&sb.st_atime));
    printf("Last file modification:   %s", ctime(&sb.st_mtime));

    exit(EXIT_SUCCESS);
}

access(2), chmod(2), chown(2), fstatat(2), readlink(2), utime(2), capabilities(7)