link, linkat - link to a file
#include <unistd.h>
int link(const char *existing, const char *new);
int linkat(int efd, const char *existing, int nfd,
const char *new, int flag);
The link() and linkat() functions create a new link (directory
entry) for the existing file and increments its link count by one. The
existing argument points to a path name naming an existing file. The
new argument points to a pathname naming the new directory entry to be
created.
To create hard links, both files must be on the same file system.
Both the old and the new link share equal access and rights to the
underlying object. Privileged processes can make multiple links to a
directory. Unless the caller is privileged, the file named by
existing must not be a directory.
The linkat() function is similar to link(). If the
path existing is a relative path, then the directory represented by
efd will be used as the starting point to resolve existing. If
the path new is a relative path, then the directory represented by
nfd will be used as the starting point to resolve new. Both
efd and nfd may be the special value AT_FDCWD which
causes the current working directory to be used as the starting point for
path resolution.
By default, linkat() does not follow symbolic links. To
cause it to follow symbolic links, the value of flag should be
AT_SYMLINK_FOLLOW.
Upon successful completion, link() and linkat() mark
for update the st_ctime field of the file. Also, the st_ctime
and st_mtime fields of the directory that contains the new entry are
marked for update.
Upon successful completion, 0 is returned. Otherwise, −1 is
returned, no link is created, and errno is set to indicate the error.
The link() and linkat() functions will fail if:
EACCES
A component of either path prefix denies search
permission, or the requested link requires writing in a directory with a mode
that denies write permission.
EDQUOT
The directory where the entry for the new link is being
placed cannot be extended because the user's quota of disk blocks on that file
system has been exhausted.
EEXIST
The link named by new exists.
EFAULT
The existing or new argument points to an
illegal address.
EILSEQ
The path argument includes non-UTF8 characters and the
file system accepts only file names where all characters are part of the UTF-8
character codeset.
EINTR
A signal was caught during the execution of the
link() or linkat() functions.
ELOOP
Too many symbolic links were encountered in translating
path.
EMLINK
The maximum number of links to a file would be
exceeded.
ENAMETOOLONG
The length of the existing or new argument
exceeds PATH_MAX, or the length of a existing or new
component exceeds NAME_MAX while _POSIX_NO_TRUNC is in
effect.
ENOENT
The existing or new argument is a null
pathname; a component of either path prefix does not exist; or the file named
by existing does not exist.
ENOLINK
The existing or new argument points to a
remote machine and the link to that machine is no longer active.
ENOSPC
The directory that would contain the link cannot be
extended.
ENOTDIR
A component of either path prefix is not a
directory.
EPERM
The file named by
existing is a directory and the
{
PRIV_SYS_LINKDIR} privilege is not asserted in the effective set of
the calling process.
The effective user ID does not match the owner of the file and the
{PRIV_FILE_LINK_ANY} privilege is not asserted in the effective set
of the calling process.
EROFS
The requested link requires writing in a directory on a
read-only file system.
EXDEV
The link named by new and the file named by
existing are on different logical devices (file systems).
The linkat() functions will fail if:
EBADF
If either existing or new is a relative
path and efd or nfd respectively are not a valid file descriptor
or the value AT_FDCWD.
EINVAL
An invalid value is set in flag. The only valid
values are 0 and fBAT_SYMLINK_FOLLOW.
ENOTDIR
If either existing or new is a relative
path and efd or nfd respectively refer to a valid descriptor
which is not a directory.
See attributes(5) for descriptions of the following attributes:
| ATTRIBUTE
TYPE |
ATTRIBUTE VALUE |
| Interface Stability |
Standard |
| MT-Level |
Async-Signal-Safe |