Tribblix: manual page: stat.2

STAT(2) System Calls STAT(2)

NAME

stat, lstat, fstat, fstatat - get file status

SYNOPSIS

#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>

int stat(const char *restrict path, struct stat *restrict buf);

int lstat(const char *restrict path, struct stat *restrict buf);

int fstat(int fildes, struct stat *buf);

int fstatat(int fildes, const char *path, struct stat *buf,
int flag);

DESCRIPTION

The stat() function obtains information about the file pointed to by
path. Read, write, or execute permission of the named file is not
required, but all directories listed in the path name leading to the
file must be searchable.

The lstat() function obtains file attributes similar to stat(),
except when the named file is a symbolic link; in that case lstat()
returns information about the link, while stat() returns information
about the file the link references.

The fstat() function obtains information about an open file known by
the file descriptor fildes, obtained from a successful open(2),
creat(2), dup(2), fcntl(2), or pipe(2) function. If fildes references
a shared memory object, the system updates in the stat structure
pointed to by the buf argument only the st_uid, st_gid, st_size, and
st_mode fields, and only the S_IRUSR, S_IWUSR, S_IRGRP, S_IWGRP,
S_IROTH, and S_IWOTH file permission bits need be valid. The system
can update other fields and flags. The fstat() function updates any
pending time-related fields before writing to the stat structure.

The fstatat() function obtains file attributes similar to the stat(),
lstat(), and fstat() functions. If the path argument is a relative
path, it is resolved relative to the fildes argument rather than the
current working directory. If path is absolute, the fildes argument
is unused. If the fildes argument has the special value AT_FDCWD,
relative paths are resolved from the current working directory. If
AT_SYMLINK_NOFOLLOW is set in the flag argument, the function behaves
like lstat() and does not automatically follow symbolic links. See
fsattr(7). If _ATTR_TRIGGER is set in the flag argument and the
vnode is a trigger mount point, the mount is performed and the
function returns the attributes of the root of the mounted
filesystem.

The buf argument is a pointer to a stat structure into which
information is placed concerning the file. A stat structure includes
the following members:

mode_t st_mode; /* File mode (see mknod(2)) */
ino_t st_ino; /* Inode number */
dev_t st_dev; /* ID of device containing */
/* a directory entry for this file */
dev_t st_rdev; /* ID of device */
/* This entry is defined only for */
/* char special or block special files */
nlink_t st_nlink; /* Number of links */
uid_t st_uid; /* User ID of the file's owner */
gid_t st_gid; /* Group ID of the file's group */
off_t st_size; /* File size in bytes */
time_t st_atime; /* Time of last access */
time_t st_mtime; /* Time of last data modification */
time_t st_ctime; /* Time of last file status change */
/* Times measured in seconds since */
/* 00:00:00 UTC, Jan. 1, 1970 */
long st_blksize; /* Preferred I/O block size */
blkcnt_t st_blocks; /* Number of 512 byte blocks allocated*/
char st_fstype[_ST_FSTYPSZ];
/* Null-terminated type of filesystem */

Descriptions of structure members are as follows:

st_mode
The mode of the file as described for the mknod()
function. In addition to the modes described on the
mknod(2) manual page, the mode of a file can also be
S_IFSOCK if the file is a socket, S_IFDOOR if the file
is a door, S_IFPORT if the file is an event port, or
S_IFLNK if the file is a symbolic link. S_IFLNK can be
returned either by lstat() or by fstatat() when the
AT_SYMLINK_NOFOLLOW flag is set.

st_ino
This field uniquely identifies the file in a given file
system. The pair st_ino and st_dev uniquely identifies
regular files.

st_dev
This field uniquely identifies the file system that
contains the file. Its value may be used as input to
the ustat() function to determine more information
about this file system. No other meaning is associated
with this value.

st_rdev
This field should be used only by administrative
commands. It is valid only for block special or
character special files and only has meaning on the
system where the file was configured.

st_nlink
This field should be used only by administrative
commands.

st_uid
The user ID of the file's owner.

st_gid
The group ID of the file's group.

st_size
For regular files, this is the address of the end of
the file. For block special or character special, this
is not defined. See also pipe(2).

st_atime
Time when file data was last accessed. Some of the
functions that change this member are: creat(),
mknod(), pipe(), utime(2), and read(2).

st_mtime
Time when data was last modified. Some of the functions
that change this member are: creat(), mknod(), pipe(),
utime(), and write(2).

st_ctime
Time when file status was last changed. Some of the
functions that change this member are: chmod(2),
chown(2), creat(2), link(2), mknod(2), pipe(2),
rename(2), unlink(2), utime(2), and write(2).

st_blksize
A hint as to the "best" unit size for I/O operations.
This field is not defined for block special or
character special files.

st_blocks
The total number of physical blocks of size 512 bytes
actually allocated on disk. This field is not defined
for block special or character special files.

st_fstype
A null-terminated string that uniquely identifies the
type of the filesystem that contains the file.

RETURN VALUES

Upon successful completion, 0 is returned. Otherwise, -1 is returned
and errno is set to indicate the error.

ERRORS

The stat(), fstat(), lstat(), and fstatat() functions will fail if:

EIO
An error occurred while reading from the file system.

EOVERFLOW
The file size in bytes or the number of blocks allocated
to the file or the file serial number cannot be
represented correctly in the structure pointed to by
buf.

The stat(), lstat(), and fstatat() functions will fail if:

EACCES
Search permission is denied for a component of the
path prefix.

EFAULT
The buf or path argument points to an illegal
address.

EINTR
A signal was caught during the execution of the
stat() or lstat() function.

ELOOP
A loop exists in symbolic links encountered during
the resolution of the path argument.

ENAMETOOLONG
The length of the path argument exceeds {PATH_MAX},
or the length of a path component exceeds {NAME_MAX}
while _POSIX_NO_TRUNC is in effect.

ENOENT
A component of path does not name an existing file or
path is an empty string.

ENOLINK
The path argument points to a remote machine and the
link to that machine is no longer active.

ENOTDIR
A component of the path prefix is not a directory, or
the fildes argument does not refer to a valid
directory when given a non-null relative path.

The fstat() and fstatat() functions will fail if:

EBADF
The fildes argument is not a valid open file descriptor.
The fildes argument to fstatat() can also have the valid
value of AT_FDCWD.

EFAULT
The buf argument points to an illegal address.

EINTR
A signal was caught during the execution of the fstat()
function.

ENOLINK
The fildes argument points to a remote machine and the
link to that machine is no longer active.

The stat(), fstat(), and lstat() functions may fail if:

EOVERFLOW
One of the members is too large to store in the stat
structure pointed to by buf.

The stat() and lstat() functions may fail if:

ELOOP
More than {SYMLOOP_MAX} symbolic links were
encountered during the resolution of the path
argument.

ENAMETOOLONG
As a result of encountering a symbolic link in
resolution of the path argument, the length of the
substituted pathname strings exceeds {PATH_MAX}.

The stat() and fstatat() functions may fail if:

ENXIO
The path argument names a character or block device special
file and the corresponding I/O device has been retired by
the fault management framework.

EXAMPLES

Example 1: Use stat() to obtain file status information.

The following example shows how to obtain file status information for
a file named /home/cnd/mod1. The structure variable buffer is defined
for the stat structure.

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
struct stat buffer;
int status;
...
status = stat("/home/cnd/mod1", &buffer);

Example 2: Use stat() to get directory information.

The following example fragment gets status information for each entry
in a directory. The call to the stat() function stores file
information in the stat structure pointed to by statbuf. The lines
that follow the stat() call format the fields in the stat structure
for presentation to the user of the program.

#include <sys/types.h>
#include <sys/stat.h>
#include <dirent.h>
#include <pwd.h>
#include <grp.h>
#include <time.h>
#include <locale.h>
#include <langinfo.h>
#include <stdio.h>
#include <stdint.h>
struct dirent *dp;
struct stat statbuf;
struct passwd *pwd;
struct group *grp;
struct tm *tm;
char datestring[256];
...
/* Loop through directory entries */
while ((dp = readdir(dir)) != NULL) {
/* Get entry's information. */
if (stat(dp->d_name, &statbuf) == -1)
continue;

/* Print out type, permissions, and number of links. */
printf("%10.10s", sperm (statbuf.st_mode));
printf("%4d", statbuf.st_nlink);

/* Print out owners name if it is found using getpwuid(). */
if ((pwd = getpwuid(statbuf.st_uid)) != NULL)
printf(" %-8.8s", pwd->pw_name);
else
printf(" %-8d", statbuf.st_uid);

/* Print out group name if it's found using getgrgid(). */
if ((grp = getgrgid(statbuf.st_gid)) != NULL)
printf(" %-8.8s", grp->gr_name);
else
printf(" %-8d", statbuf.st_gid);

/* Print size of file. */
printf(" %9jd", (intmax_t)statbuf.st_size);
tm = localtime(&statbuf.st_mtime);

/* Get localized date string. */
strftime(datestring, sizeof(datestring), nl_langinfo(D_T_FMT), tm);

printf(" %s %s\n", datestring, dp->d_name);
}

Example 3: Use fstat() to obtain file status information.

The following example shows how to obtain file status information for
a file named /home/cnd/mod1. The structure variable buffer is defined
for the stat structure. The /home/cnd/mod1 file is opened with
read/write privileges and is passed to the open file descriptor
fildes.

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
struct stat buffer;
int status;
...
fildes = open("/home/cnd/mod1", O_RDWR);
status = fstat(fildes, &buffer);

Example 4: Use lstat() to obtain symbolic link status information.

The following example shows how to obtain status information for a
symbolic link named /modules/pass1. The structure variable buffer is
defined for the stat structure. If the path argument specified the
filename for the file pointed to by the symbolic link
(/home/cnd/mod1), the results of calling the function would be the
same as those returned by a call to the stat() function.

#include <sys/stat.h>
struct stat buffer;
int status;
...
status = lstat("/modules/pass1", &buffer);

USAGE

If chmod() or fchmod() is used to change the file group owner
permissions on a file with non-trivial ACL entries, only the ACL mask
is set to the new permissions and the group owner permission bits in
the file's mode field (defined in mknod(2)) are unchanged. A non-
trivial ACL entry is one whose meaning cannot be represented in the
file's mode field alone. The new ACL mask permissions might change
the effective permissions for additional users and groups that have
ACL entries on the file.

The stat(), fstat(), and lstat() functions have transitional
interfaces for 64-bit file offsets. See lf64(7).

ATTRIBUTES