link man page
link, linkat — make a new name for a file
#include <unistd.h> int link(const char *oldpath, const char *newpath); #include <fcntl.h> /* Definition of AT_* constants */ #include <unistd.h> int linkat(int olddirfd, const char *oldpath, int newdirfd, const char *newpath, int flags);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
- Since glibc 2.10:
_POSIX_C_SOURCE >= 200809L
- Before glibc 2.10:
link() creates a new link (also known as a hard link) to an existing file.
If newpath exists, it will not be overwritten.
This new name may be used exactly as the old one for any operation; both names refer to the same file (and so have the same permissions and ownership) and it is impossible to tell which name was the "original".
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
Write access to the directory containing newpath is denied, or search permission is denied for one of the directories in the path prefix of oldpath or newpath. (See also path_resolution(7).)
The user's quota of disk blocks on the filesystem has been exhausted.
newpath already exists.
oldpath or newpath points outside your accessible address space.
An I/O error occurred.
Too many symbolic links were encountered in resolving oldpath or newpath.
The file referred to by oldpath already has the maximum number of links to it. For example, on an ext4(5) filesystem that does not employ the dir_index feature, the limit on the number of hard links to a file is 65,000; on btrfs(5), the limit is 65,535 links.
oldpath or newpath was too long.
A directory component in oldpath or newpath does not exist or is a dangling symbolic link.
Insufficient kernel memory was available.
The device containing the file has no room for the new directory entry.
A component used as a directory in oldpath or newpath is not, in fact, a directory.
oldpath is a directory.
The filesystem containing oldpath and newpath does not support the creation of hard links.
- EPERM (since Linux 3.6)
The caller does not have permission to create a hard link to this file (see the description of /proc/sys/fs/protected_hardlinks in proc(5)).
oldpath is marked immutable or append-only. (See ioctl_iflags(2).)
The file is on a read-only filesystem.
oldpath and newpath are not on the same mounted filesystem. (Linux permits a filesystem to be mounted at multiple points, but link() does not work across different mount points, even if the same filesystem is mounted on both.)
The following additional errors can occur for linkat():
olddirfd or newdirfd is not a valid file descriptor.
An invalid flag value was specified in flags.
AT_EMPTY_PATH was specified in flags, but the caller did not have the CAP_DAC_READ_SEARCH capability.
An attempt was made to link to the /proc/self/fd/NN file corresponding to a file descriptor created with
open(path, O_TMPFILE | O_EXCL, mode);
oldpath is a relative pathname and olddirfd refers to a directory that has been deleted, or newpath is a relative pathname and newdirfd refers to a directory that has been deleted.
oldpath is relative and olddirfd is a file descriptor referring to a file other than a directory; or similar for newpath and newdirfd
AT_EMPTY_PATH was specified in flags, oldpath is an empty string, and olddirfd refers to a directory.
linkat() was added to Linux in kernel 2.6.16; library support was added to glibc in version 2.4.
link(): SVr4, 4.3BSD, POSIX.1-2001 (but see Notes), POSIX.1-2008.
Hard links, as created by link(), cannot span filesystems. Use symlink(2) if this is required.
POSIX.1-2001 says that link() should dereference oldpath if it is a symbolic link. However, since kernel 2.0, Linux does not do so: if oldpath is a symbolic link, then newpath is created as a (hard) link to the same symbolic link file (i.e., newpath becomes a symbolic link to the same file that oldpath refers to). Some other implementations behave in the same manner as Linux. POSIX.1-2008 changes the specification of link(), making it implementation-dependent whether or not oldpath is dereferenced if it is a symbolic link. For precise control over the treatment of symbolic links when creating a link, use linkat().
On older kernels where linkat() is unavailable, the glibc wrapper function falls back to the use of link(), unless the AT_SYMLINK_FOLLOW is specified. When oldpath and newpath are relative pathnames, glibc constructs pathnames based on the symbolic links in /proc/self/fd that correspond to the olddirfd and newdirfd arguments.
On NFS filesystems, the return code may be wrong in case the NFS server performs the link creation and dies before it can say so. Use stat(2) to find out if the link got created.
ln(1), open(2), rename(2), stat(2), symlink(2), unlink(2), path_resolution(7), symlink(7)
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
capabilities(7), dotlockfile(1), explain(1), explain(3), explain_link(3), explain_linkat(3), explain_linkat_or_die(3), explain_link_or_die(3), fcntl(2), inode(7), inotify(7), jpegoptim(1), link(1), ln(1), lockfile_create(3), mbox(5), mmdf(5), nfslogsum(8), ocfs2(7), open(2), open_excl(3), remove(3), rename(2), signal-safety(7), sshfs(1), star(1), symlink(2), symlink(7), syscalls(2), tar_extract_file(3), unlink(2).
The man page linkat(2) is an alias of link(2).