prctl.2: ffix

[thirdparty/man-pages.git] / man2 / stat.2

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.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
.\" Parts Copyright (c) 1995 Nicolai Langfeldt (janl@ifi.uio.no), 1/1/95
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.\" Modified by Michael Haardt <michael@moria.de>
.\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
.\" Modified 1995-05-18 by Todd Larason <jtl@molehill.org>
.\" Modified 1997-01-31 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified 1995-01-09 by Richard Kettlewell <richard@greenend.org.uk>
.\" Modified 1998-05-13 by Michael Haardt <michael@cantor.informatik.rwth-aachen.de>
.\" Modified 1999-07-06 by aeb & Albert Cahalan
.\" Modified 2000-01-07 by aeb
.\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
.\" 2007-06-08 mtk: Added example program
.\" 2007-07-05 mtk: Added details on underlying system call interfaces
.\"
.TH STAT 2 2019-03-06 "Linux" "Linux Programmer's Manual"
.SH NAME
stat, fstat, lstat, fstatat \- get file status
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.B #include <sys/stat.h>
.B #include <unistd.h>
.PP
.BI "int stat(const char *" pathname ", struct stat *" statbuf );
.BI "int fstat(int " fd ", struct stat *" statbuf );
.BI "int lstat(const char *" pathname ", struct stat *" statbuf );

.BR "#include <fcntl.h>           " "/* Definition of AT_* constants */"
.B #include <sys/stat.h>
.PP
.BI "int fstatat(int " dirfd ", const char *" pathname ", struct stat *" \
statbuf ,
.BI "            int " flags );
.fi
.PP
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.PP
.ad l
.BR lstat ():
.RS 4
/* glibc 2.19 and earlier */ _BSD_SOURCE
.br
    || /* Since glibc 2.20 */ _DEFAULT_SOURCE
.br
    || _XOPEN_SOURCE\ >=\ 500
.\"   _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
.br
    || /* Since glibc 2.10: */ _POSIX_C_SOURCE\ >=\ 200112L
.RE
.PP
.BR fstatat ():
.ad l
.RS 4
.PD 0
.TP 4
Since glibc 2.10:
_POSIX_C_SOURCE\ >=\ 200809L
.TP
Before glibc 2.10:
_ATFILE_SOURCE
.RE
.PD
.ad
.SH DESCRIPTION
.PP
These functions return information about a file, in the buffer pointed to by
.IR statbuf .
No permissions are required on the file itself, but\(emin the case of
.BR stat (),
.BR fstatat (),
and
.BR lstat ()\(emexecute
(search) permission is required on all of the directories in
.I pathname
that lead to the file.
.PP
.BR stat ()
and
.BR fstatat ()
retrieve information about the file pointed to by
.IR pathname ;
the differences for
.BR fstatat ()
are described below.
.PP
.BR lstat ()
is identical to
.BR stat (),
except that if
.I pathname
is a symbolic link, then it returns information about the link itself,
not the file that it refers to.
.PP
.BR fstat ()
is identical to
.BR stat (),
except that the file about which information is to be retrieved
is specified by the file descriptor
.IR fd .
.\"
.SS The stat structure
All of these system calls return a
.I stat
structure, which contains the following fields:
.PP
.in +4n
.EX
struct stat {
    dev_t     st_dev;         /* ID of device containing file */
    ino_t     st_ino;         /* Inode number */
    mode_t    st_mode;        /* File type and mode */
    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;     /* Block size for filesystem I/O */
    blkcnt_t  st_blocks;      /* Number of 512B blocks allocated */

    /* Since Linux 2.6, the kernel supports nanosecond
       precision for the following timestamp fields.
       For the details before Linux 2.6, see NOTES. */

    struct timespec st_atim;  /* Time of last access */
    struct timespec st_mtim;  /* Time of last modification */
    struct timespec st_ctim;  /* Time of last status change */

#define st_atime st_atim.tv_sec      /* Backward compatibility */
#define st_mtime st_mtim.tv_sec
#define st_ctime st_ctim.tv_sec
};
.EE
.in
.PP
.IR Note :
the order of fields in the
.I stat
structure varies somewhat
across architectures.
In addition,
the definition above does not show the padding bytes
that may be present between some fields on various architectures.
Consult the glibc and kernel source code
if you need to know the details.
.PP
.\" Background: inode attributes are modified with i_mutex held, but
.\" read by stat() without taking the mutex.
.IR Note :
for performance and simplicity reasons, different fields in the
.I stat
structure may contain state information from different moments
during the execution of the system call.
For example, if
.IR st_mode
or
.IR st_uid
is changed by another process by calling
.BR chmod (2)
or
.BR chown (2),
.BR stat ()
might return the old
.I st_mode
together with the new
.IR st_uid ,
or the old
.I st_uid
together with the new
.IR st_mode .
.PP
The fields in the
.I stat
structure are as follows:
.TP
.I st_dev
This field describes the device on which this file resides.
(The
.BR major (3)
and
.BR minor (3)
macros may be useful to decompose the device ID in this field.)
.TP
.I st_ino
This field contains the file's inode number.
.TP
.I st_mode
This field contains the file type and mode.
See
.BR inode (7)
for further information.
.TP
.I st_nlink
This field contains the number of hard links to the file.
.TP
.I st_uid
This field contains the user ID of the owner of the file.
.TP
.I st_gid
This field contains the ID of the group owner of the file.
.TP
.I st_rdev
This field describes the device that this file (inode) represents.
.TP
.I st_size
This field gives the size of the file (if it is a regular
file or a symbolic link) in bytes.
The size of a symbolic link is the length of the pathname
it contains, without a terminating null byte.
.TP
.I st_blksize
This field gives the "preferred" block size for efficient filesystem I/O.
.TP
.I st_blocks
This field indicates the number of blocks allocated to the file,
in 512-byte units.
(This may be smaller than
.IR st_size /512
when the file has holes.)
.TP
.I st_atime
This is the file's last access timestamp.
.TP
.I st_mtime
This is the file's last modification timestamp.
.TP
.I st_ctime
This is the file's last status change timestamp.
.PP
For further information on the above fields, see
.BR inode (7).
.\"
.SS fstatat()
The
.BR fstatat ()
system call is a more general interface for accessing file information
which can still provide exactly the behavior of each of
.BR stat (),
.BR lstat (),
and
.BR fstat ().
.PP
If the pathname given in
.I pathname
is relative, then it is interpreted relative to the directory
referred to by the file descriptor
.I dirfd
(rather than relative to the current working directory of
the calling process, as is done by
.BR stat ()
and
.BR lstat ()
for a relative pathname).
.PP
If
.I pathname
is relative and
.I dirfd
is the special value
.BR AT_FDCWD ,
then
.I pathname
is interpreted relative to the current working
directory of the calling process (like
.BR stat ()
and
.BR lstat ()).
.PP
If
.I pathname
is absolute, then
.I dirfd
is ignored.
.PP
.I flags
can either be 0, or include one or more of the following flags ORed:
.TP
.BR AT_EMPTY_PATH " (since Linux 2.6.39)"
.\" commit 65cfc6722361570bfe255698d9cd4dccaf47570d
If
.I pathname
is an empty string, operate on the file referred to by
.IR dirfd
(which may have been obtained using the
.BR open (2)
.B O_PATH
flag).
In this case,
.I dirfd
can refer to any type of file, not just a directory, and
the behavior of
.BR fstatat ()
is similar to that of
.BR fstat ().
If
.I dirfd
is
.BR AT_FDCWD ,
the call operates on the current working directory.
This flag is Linux-specific; define
.B _GNU_SOURCE
.\" Before glibc 2.16, defining _ATFILE_SOURCE sufficed
to obtain its definition.
.TP
.BR AT_NO_AUTOMOUNT " (since Linux 2.6.38)"
Don't automount the terminal ("basename") component of
.I pathname
if it is a directory that is an automount point.
This allows the caller to gather attributes of an automount point
(rather than the location it would mount).
Since Linux 4.14,
.\" commit 42f46148217865a545e129612075f3d828a2c4e4
also don't instantiate a nonexistent name in an
on-demand directory such as used for automounter indirect maps.
This flag can be used in tools that scan directories
to prevent mass-automounting of a directory of automount points.
The
.B AT_NO_AUTOMOUNT
flag has no effect if the mount point has already been mounted over.
This flag is Linux-specific; define
.B _GNU_SOURCE
.\" Before glibc 2.16, defining _ATFILE_SOURCE sufficed
to obtain its definition.
Both
.BR stat ()
and
.BR lstat ()
act as though
.B AT_NO_AUTOMOUNT
was set.
.TP
.B AT_SYMLINK_NOFOLLOW
If
.I pathname
is a symbolic link, do not dereference it:
instead return information about the link itself, like
.BR lstat ().
(By default,
.BR fstatat ()
dereferences symbolic links, like
.BR stat ().)
.PP
See
.BR openat (2)
for an explanation of the need for
.BR fstatat ().
.SH RETURN VALUE
On success, zero is returned.
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EACCES
Search permission is denied for one of the directories
in the path prefix of
.IR pathname .
(See also
.BR path_resolution (7).)
.TP
.B EBADF
.I fd
is not a valid open file descriptor.
.TP
.B EFAULT
Bad address.
.TP
.B ELOOP
Too many symbolic links encountered while traversing the path.
.TP
.B ENAMETOOLONG
.I pathname
is too long.
.TP
.B ENOENT
A component of
.I pathname
does not exist or is a dangling symbolic link.
.TP
.B ENOENT
.I pathname
is an empty string and
.B AT_EMPTY_PATH
was not specified in
.IR flags .
.TP
.B ENOMEM
Out of memory (i.e., kernel memory).
.TP
.B ENOTDIR
A component of the path prefix of
.I pathname
is not a directory.
.TP
.B EOVERFLOW
.I pathname
or
.I fd
refers to a file whose size, inode number,
or number of blocks cannot be represented in, respectively, the types
.IR off_t ,
.IR ino_t ,
or
.IR blkcnt_t .
This error can occur when, for example,
an application compiled on a 32-bit platform without
.I -D_FILE_OFFSET_BITS=64
calls
.BR stat ()
on a file whose size exceeds
.I (1<<31)-1
bytes.
.PP
The following additional errors can occur for
.BR fstatat ():
.TP
.B EBADF
.I dirfd
is not a valid file descriptor.
.TP
.B EINVAL
Invalid flag specified in
.IR flags .
.TP
.B ENOTDIR
.I pathname
is relative and
.I dirfd
is a file descriptor referring to a file other than a directory.
.SH VERSIONS
.BR fstatat ()
was added to Linux in kernel 2.6.16;
library support was added to glibc in version 2.4.
.SH CONFORMING TO
.BR stat (),
.BR fstat (),
.BR lstat ():
SVr4, 4.3BSD, POSIX.1-2001, POSIX.1.2008.
.\" SVr4 documents additional
.\" .BR fstat ()
.\" error conditions EINTR, ENOLINK, and EOVERFLOW.  SVr4
.\" documents additional
.\" .BR stat ()
.\" and
.\" .BR lstat ()
.\" error conditions EINTR, EMULTIHOP, ENOLINK, and EOVERFLOW.
.PP
.BR fstatat ():
POSIX.1-2008.
.PP
According to POSIX.1-2001,
.BR lstat ()
on a symbolic link need return valid information only in the
.I st_size
field and the file type of the
.IR st_mode
field of the
.IR stat
structure.
POSIX.1-2008 tightens the specification, requiring
.BR lstat ()
to return valid information in all fields except the mode bits in
.IR st_mode .
.PP
Use of the
.I st_blocks
and
.I 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.)
.SH NOTES
.SS Timestamp fields
Older kernels and older standards did not support nanosecond timestamp
fields.
Instead, there were three timestamp
.RI fields\(em st_atime ,
.IR st_mtime ,
and
.IR st_ctime \(emtyped
as
.IR time_t
that recorded timestamps with one-second precision.
.PP
Since kernel 2.5.48, the
.I stat
structure supports nanosecond resolution for the three file timestamp fields.
The nanosecond components of each timestamp are available
via names of the form
.IR st_atim.tv_nsec ,
if suitable feature test macros are defined.
Nanosecond timestamps were standardized in POSIX.1-2008,
and, starting with version 2.12,
glibc exposes the nanosecond component names if
.BR _POSIX_C_SOURCE
is defined with the value 200809L or greater, or
.BR _XOPEN_SOURCE
is defined with the value 700 or greater.
Up to and including glibc 2.19,
the definitions of the nanoseconds components are also defined if
.B _BSD_SOURCE
or
.B _SVID_SOURCE
is defined.
If none of the aforementioned macros are defined,
then the nanosecond values are exposed with names of the form
.IR st_atimensec .
.\"
.SS C library/kernel differences
Over time, increases in the size of the
.I stat
structure have led to three successive versions of
.BR stat ():
.IR sys_stat ()
(slot
.IR __NR_oldstat ),
.IR sys_newstat ()
(slot
.IR __NR_stat ),
and
.I sys_stat64()
(slot
.IR __NR_stat64 )
on 32-bit platforms such as i386.
The first two versions were already present in Linux 1.0
(albeit with different names);
.\" See include/asm-i386/stat.h in the Linux 2.4 source code for the
.\" various versions of the structure definitions
the last was added in Linux 2.4.
Similar remarks apply for
.BR fstat ()
and
.BR lstat ().
.PP
The kernel-internal versions of the
.I stat
structure dealt with by the different versions are, respectively:
.TP
.IR __old_kernel_stat
The original structure, with rather narrow fields, and no padding.
.TP
.IR stat
Larger
.I st_ino
field and padding added to various parts of the structure to
allow for future expansion.
.TP
.IR stat64
Even larger
.I st_ino
field,
larger
.I st_uid
and
.I st_gid
fields to accommodate the Linux-2.4 expansion of UIDs and GIDs to 32 bits,
and various other enlarged fields and further padding in the structure.
(Various padding bytes were eventually consumed in Linux 2.6,
with the advent of 32-bit device IDs and nanosecond components
for the timestamp fields.)
.PP
The glibc
.BR stat ()
wrapper function hides these details from applications,
invoking the most recent version of the system call provided by the kernel,
and repacking the returned information if required for old binaries.
.\"
.\" A note from Andries Brouwer, July 2007
.\"
.\" > Is the story not rather more complicated for some calls like
.\" > stat(2)?
.\"
.\" Yes and no, mostly no. See /usr/include/sys/stat.h .
.\"
.\" The idea is here not so much that syscalls change, but that
.\" the definitions of struct stat and of the types dev_t and mode_t change.
.\" This means that libc (even if it does not call the kernel
.\" but only calls some internal function) must know what the
.\" format of dev_t or of struct stat is.
.\" The communication between the application and libc goes via
.\" the include file <sys/stat.h> that defines a _STAT_VER and
.\" _MKNOD_VER describing the layout of the data that user space
.\" uses. Each (almost each) occurrence of stat() is replaced by
.\" an occurrence of xstat() where the first parameter of xstat()
.\" is this version number _STAT_VER.
.\"
.\" Now, also the definitions used by the kernel change.
.\" But glibc copes with this in the standard way, and the
.\" struct stat as returned by the kernel is repacked into
.\" the struct stat as expected by the application.
.\" Thus, _STAT_VER and this setup cater for the application-libc
.\" interface, rather than the libc-kernel interface.
.\"
.\" (Note that the details depend on gcc being used as c compiler.)
.PP
On modern 64-bit systems, life is simpler: there is a single
.BR stat ()
system call and the kernel deals with a
.I stat
structure that contains fields of a sufficient size.
.PP
The underlying system call employed by the glibc
.BR fstatat ()
wrapper function is actually called
.BR fstatat64 ()
or, on some architectures,
.\" strace(1) shows the name "newfstatat" on x86-64
.BR newfstatat ().
.SH EXAMPLE
The following program calls
.BR lstat ()
and displays selected fields in the returned
.I stat
structure.
.PP
.EX
#include <sys/types.h>
#include <sys/stat.h>
#include <time.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/sysmacros.h>

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

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

    if (lstat(argv[1], &sb) == \-1) {
        perror("lstat");