wait4.2: Fix feature test macro requirements

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

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.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
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.TH STAT 2 2009-09-30 "Linux" "Linux Programmer's Manual"
.SH NAME
stat, fstat, lstat \- get file status
.SH SYNOPSIS
.B #include <sys/types.h>
.br
.B #include <sys/stat.h>
.br
.B #include <unistd.h>
.sp
.BI "int stat(const char *" path ", struct stat *" buf );
.br
.BI "int fstat(int " fd ", struct stat *" buf );
.br
.BI "int lstat(const char *" path ", struct stat *" buf );
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR lstat ():
_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
.SH DESCRIPTION
.PP
These functions return information about a file.
No permissions are required on the file itself, but \(em in the case of
.BR stat ()
and
.BR lstat ()
\(em
execute (search) permission is required on all of the directories in
.I path
that lead to the file.
.PP
.BR stat ()
stats the file pointed to by
.I path
and fills in
.IR buf .

.BR lstat ()
is identical to
.BR stat (),
except that if
.I path
is a symbolic link, then the link itself is stat-ed,
not the file that it refers to.

.BR fstat ()
is identical to
.BR stat (),
except that the file to be stat-ed is specified by the file descriptor
.IR fd .
.PP
All of these system calls return a
.I stat
structure, which contains the following fields:
.PP
.in +4n
.nf
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 512B 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 */
};
.fi
.in
.PP
The
.I st_dev
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.)

The
.I st_rdev
field describes the device that this file (inode) represents.

The
.I 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
.I st_blocks
field indicates the number of blocks allocated to the file, 512-byte units.
(This may be smaller than
.IR st_size /512
when the file has holes.)

The
.I 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.)
.PP
Not all of the Linux file systems implement all of the time fields.
Some file system types allow mounting in such a way that file
and/or directory accesses do not cause an update of the
.I st_atime
field.
(See
.IR noatime ,
.IR nodiratime ,
and
.I relatime
in
.BR mount (8),
and related information in
.BR mount (2).)
In addition,
.I st_atime
is not updated if a file is opened with the
.BR O_NOATIME ;
see
.BR open (2).

The field
.I st_atime
is changed by file accesses, for example, by
.BR execve (2),
.BR mknod (2),
.BR pipe (2),
.BR utime (2)
and
.BR read (2)
(of more than zero bytes).
Other routines, like
.BR mmap (2),
may or may not update
.IR st_atime .

The field
.I st_mtime
is changed by file modifications, for example, by
.BR mknod (2),
.BR truncate (2),
.BR utime (2)
and
.BR write (2)
(of more than zero bytes).
Moreover,
.I st_mtime
of a directory is changed by the creation or deletion of files
in that directory.
The
.I st_mtime
field is
.I not
changed for changes in owner, group, hard link count, or mode.

The field
.I st_ctime
is changed by writing or by setting inode information
(i.e., owner, group, link count, mode, etc.).
.PP
The following POSIX macros are defined to check the file type using the
.I st_mode
field:
.RS 4
.TP 1.2i
.BR S_ISREG (m)
is it a regular file?
.TP
.BR S_ISDIR (m)
directory?
.TP
.BR S_ISCHR (m)
character device?
.TP
.BR S_ISBLK (m)
block device?
.TP
.BR S_ISFIFO (m)
FIFO (named pipe)?
.TP
.BR S_ISLNK (m)
symbolic link? (Not in POSIX.1-1996.)
.TP
.BR S_ISSOCK (m)
socket? (Not in POSIX.1-1996.)
.RE
.PP
The following flags are defined for the
.I st_mode
field:
.in +4n
.TS
lB l l.
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
.TE
.in
.P
The set-group-ID bit
.RB ( 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
.B S_ISGID
bit set.
For a file that does not have the group execution bit
.RB ( S_IXGRP )
set,
the set-group-ID bit indicates mandatory file/record locking.
.P
The sticky bit
.RB ( 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.
.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 path .
(See also
.BR path_resolution (7).)
.TP
.B EBADF
.I fd
is bad.
.TP
.B EFAULT
Bad address.
.TP
.B ELOOP
Too many symbolic links encountered while traversing the path.
.TP
.B ENAMETOOLONG
File name too long.
.TP
.B ENOENT
A component of
.I path
does not exist, or
.I path
is an empty string.
.TP
.B ENOMEM
Out of memory (i.e., kernel memory).
.TP
.B ENOTDIR
A component of the path prefix of
.I path
is not a directory.
.TP
.B EOVERFLOW
.RB ( stat ())
.I path