readlink

, readlinkat

- read the contents of a symbolic link

Synopsis

#include <unistd.h>

ssize_t readlink(const char *restrict path, char *restrict buf, 
     size_t bufsiz);

ssize_t readlinkat(int fd, const char *restrict path,
char *restrict buf, size_t bufsize);

Description

The readlink() function places the contents of the symbolic link referred to by path in the buffer buf which has size bufsiz. If the number of bytes in the symbolic link is less than bufsiz, the contents of the remainder of buf are left unchanged. If the buf argument is not large enough to contain the link content, the first bufsize bytes are placed in buf.

Upon successful completion, readlink() marks for update the last data access timestamp of the symbolic link.

The readlinkat() function is equivalent to the readlink() function except in the case where path specifies a relative path. In this case the symbolic link whose content is read is relative to the directory associated with the file descriptor fd instead of the current working directory. If the file descriptor was opened without O_SEARCH, the function checks whether directory searches are permitted using the current permissions of the directory underlying the file descriptor. If the file descriptor was opened with O_SEARCH, the function does not perform the check.

If readlinkat() is passed the special value AT_FDCWD in the fd parameter, the current working directory is used and the behavior is identical to a call to readlink().

Return Values

Upon successful completion, readlink() and readlinkat() return the count of bytes placed in the buffer. Otherwise, it returns -1, leaves the buffer unchanged, and sets errno to indicate the error.

Errors

The readlink() and readlinkat() functions will fail if:

EACCES

Search permission is denied for a component of the path prefix of path.

EFAULT

path or buf points to an illegal address.

EINVAL

The path argument names a file that is not a symbolic link.

EIO

An I/O error occurred while reading from the file system.

ENOENT

A component of path does not name an existing file or path is an empty string.

ELOOP

A loop exists in symbolic links encountered during resolution of the path argument.

ENAMETOOLONG

The length of path exceeds {PATH_MAX}, or a pathname component is longer than {NAME_MAX} while _POSIX_NO_TRUNC is in effect.

ENOTDIR

A component of the path prefix is not a directory.

ENOSYS

The file system does not support symbolic links.

The readlinkat() function will fail if:

EACCES

fd was not opened with O_SEARCH and the permissions of the directory underlying fd do not permit directory searches.

EBADF

The path 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.

The readlink() and readlinkat() functions may fail if:

EACCES

Read permission is denied for the directory.

ELOOP

More than {SYMLOOP_MAX} symbolic links were encountered in resolving path.

ENAMETOOLONG

As a result of encountering a symbolic link in resolution of the path argument, the length of the substituted pathname string exceeded {PATH_MAX}.

The readlinkat() function may fail if:

ENOTDIR

The path argument is not an absolute path and fd is neither AT_FDCWD nor a file descriptor associated with a directory.

Usage

Portable applications should not assume that the returned contents of the symbolic link are null-terminated.

Attributes

See attributes(5) for descriptions of the following attributes:

See Also

stat(2), symlink(2), attributes(5), standards(5)