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Copyright (c) 2014, Joyent, Inc.
Copyright 1989 AT&T
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#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.
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.
The link named by new exists.
The existing or new argument points to an illegal address.
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.
A signal was caught during the execution of the link() or linkat() functions.
Too many symbolic links were encountered in translating path.
The maximum number of links to a file would be exceeded.
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.
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.
The existing or new argument points to a remote machine and the link to that machine is no longer active.
The directory that would contain the link cannot be extended.
A component of either path prefix is not a directory.
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.
The requested link requires writing in a directory on a read-only file system.
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.
An invalid value is set in flag. The only valid values are 0 and fBAT_SYMLINK_FOLLOW.
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 |
symlink(2), unlink(2), attributes(5), privileges(5), standards(5)