сделать символическую ссылку (make a symbolic link)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
symlink, symlinkat — make a symbolic link
Синопсис (Synopsis)
#include <unistd.h>
int symlink(const char *path1, const char *path2);
#include <fcntl.h>
int symlinkat(const char *path1, int fd, const char *path2);
Описание (Description)
The symlink() function shall create a symbolic link called path2
that contains the string pointed to by path1 (path2 is the name
of the symbolic link created, path1 is the string contained in
the symbolic link).
The string pointed to by path1 shall be treated only as a string
and shall not be validated as a pathname.
If the symlink() function fails for any reason other than [EIO],
any file named by path2 shall be unaffected.
If path2 names a symbolic link, symlink() shall fail and set
errno to [EEXIST].
The symbolic link's user ID shall be set to the process'
effective user ID. The symbolic link's group ID shall be set to
the group ID of the parent directory or to the effective group ID
of the process. Implementations shall provide a way to initialize
the symbolic link's group ID to the group ID of the parent
directory. Implementations may, but need not, provide an
implementation-defined way to initialize the symbolic link's
group ID to the effective group ID of the calling process.
The values of the file mode bits for the created symbolic link
are unspecified. All interfaces specified by POSIX.1‐2008 shall
behave as if the contents of symbolic links can always be read,
except that the value of the file mode bits returned in the
st_mode field of the stat structure is unspecified.
Upon successful completion, symlink() shall mark for update the
last data access, last data modification, and last file status
change timestamps of the symbolic link. Also, the last data
modification and last file status change timestamps of the
directory that contains the new entry shall be marked for update.
The symlinkat() function shall be equivalent to the symlink()
function except in the case where path2 specifies a relative
path. In this case the symbolic link is created relative to the
directory associated with the file descriptor fd instead of the
current working directory. If the access mode of the open file
description associated with the file descriptor is not O_SEARCH,
the function shall check whether directory searches are permitted
using the current permissions of the directory underlying the
file descriptor. If the access mode is O_SEARCH, the function
shall not perform the check.
If symlinkat() is passed the special value AT_FDCWD in the fd
parameter, the current working directory shall be used and the
behavior shall be identical to a call to symlink().
Возвращаемое значение (Return value)
Upon successful completion, these functions shall return 0.
Otherwise, these functions shall return -1 and set errno to
indicate the error.
Ошибки (Error)
These functions shall fail if:
EACCES Write permission is denied in the directory where the
symbolic link is being created, or search permission is
denied for a component of the path prefix of path2.
EEXIST The path2 argument names an existing file.
EIO An I/O error occurs while reading from or writing to the
file system.
ELOOP A loop exists in symbolic links encountered during
resolution of the path2 argument.
ENAMETOOLONG
The length of a component of the pathname specified by the
path2 argument is longer than {NAME_MAX} or the length of
the path1 argument is longer than {SYMLINK_MAX}.
ENOENT A component of the path prefix of path2 does not name an
existing file or path2 is an empty string.
ENOENT or ENOTDIR
The path2 argument contains at least one non-<slash>
character and ends with one or more trailing <slash>
characters. If path2 without the trailing <slash>
characters would name an existing file, an [ENOENT] error
shall not occur.
ENOSPC The directory in which the entry for the new symbolic link
is being placed cannot be extended because no space is
left on the file system containing the directory, or the
new symbolic link cannot be created because no space is
left on the file system which shall contain the link, or
the file system is out of file-allocation resources.
ENOTDIR
A component of the path prefix of path2 names an existing
file that is neither a directory nor a symbolic link to a
directory.
EROFS The new symbolic link would reside on a read-only file
system.
The symlinkat() function shall fail if:
EACCES The access mode of the open file description associated
with fd is not O_SEARCH and the permissions of the
directory underlying fd do not permit directory searches.
EBADF The path2 argument does not specify an absolute path and
the fd argument is neither AT_FDCWD nor a valid file
descriptor open for reading or searching.
ENOTDIR
The path2 argument is not an absolute path and fd is a
file descriptor associated with a non-directory file.
These functions may fail if:
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered
during resolution of the path2 argument.
ENAMETOOLONG
The length of the path2 argument exceeds {PATH_MAX} or
pathname resolution of a symbolic link in the path2
argument produced an intermediate result with a length
that exceeds {PATH_MAX}.
The following sections are informative.
Примеры (Examples)
None.
Использование в приложениях (Application usage)
Like a hard link, a symbolic link allows a file to have multiple
logical names. The presence of a hard link guarantees the
existence of a file, even after the original name has been
removed. A symbolic link provides no such assurance; in fact, the
file named by the path1 argument need not exist when the link is
created. A symbolic link can cross file system boundaries.
Normal permission checks are made on each component of the
symbolic link pathname during its resolution.
Обоснование (Rationale)
The purpose of the symlinkat() function is to create symbolic
links in directories other than the current working directory
without exposure to race conditions. Any part of the path of a
file could be changed in parallel to a call to symlink(),
resulting in unspecified behavior. By opening a file descriptor
for the target directory and using the symlinkat() function it
can be guaranteed that the created symbolic link is located
relative to the desired directory.
Будущие направления (Future directions)
None.
Смотри также (See also)
fdopendir(3p), fstatat(3p), lchown(3p), link(3p), open(3p),
readlink(3p), rename(3p), unlink(3p)
The Base Definitions volume of POSIX.1‐2017, fcntl.h(0p),
unistd.h(0p)
