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link - make a new name for a file
#include <unistd.h> int link(const char *oldpath, const char *newpath);
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.
EACCES 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).) EEXIST newpath already exists. EFAULT oldpath or newpath points outside your accessible address space. EIO An I/O error occurred. ELOOP Too many symbolic links were encountered in resolving oldpath or newpath. EMLINK The file referred to by oldpath already has the maximum number of links to it. ENAMETOOLONG oldpath or newpath was too long. ENOENT A directory component in oldpath or newpath does not exist or is a dangling symbolic link. ENOMEM Insufficient kernel memory was available. ENOSPC The device containing the file has no room for the new directory entry. ENOTDIR A component used as a directory in oldpath or newpath is not, in fact, a directory. EPERM oldpath is a directory. EPERM The file system containing oldpath and newpath does not support the creation of hard links. EROFS The file is on a read-only file system. EXDEV oldpath and newpath are not on the same mounted file system. (Linux permits a file system to be mounted at multiple points, but link() does not work across different mount points, even if the same file system is mounted on both.)
SVr4, 4.3BSD, POSIX.1-2001 (but see NOTES).
Hard links, as created by link(), cannot span file systems. 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, see linkat(2).
On NFS file systems, 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), linkat(2), open(2), rename(2), stat(2), symlink(2), unlink(2), path_resolution(7), symlink(7)
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