NAME

       readlink - read value of a symbolic link

SYNOPSIS

       #include <unistd.h>

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

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       readlink():
           _BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED ||
           _POSIX_C_SOURCE >= 200112L

DESCRIPTION

       readlink()  places  the  contents  of  the  symbolic  link path in the buffer buf, which has size bufsiz.
       readlink() does not append a null byte to buf.  It will truncate the contents  (to  a  length  of  bufsiz
       characters), in case the buffer is too small to hold all of the contents.

RETURN VALUE

       On  success, readlink() returns the number of bytes placed in buf.  On error, -1 is returned and errno is
       set to indicate the error.

ERRORS

       EACCES Search permission is denied for a component of the path prefix.  (See also path_resolution(7).)

       EFAULT buf extends outside the process's allocated address space.

       EINVAL bufsiz is not positive.

       EINVAL The named file is not a symbolic link.

       EIO    An I/O error occurred while reading from the filesystem.

       ELOOP  Too many symbolic links were encountered in translating the pathname.

       ENAMETOOLONG
              A pathname, or a component of a pathname, was too long.

       ENOENT The named file does not exist.

       ENOMEM Insufficient kernel memory was available.

       ENOTDIR
              A component of the path prefix is not a directory.

CONFORMING TO

       4.4BSD (readlink() first appeared in 4.2BSD), POSIX.1-2001.

NOTES

       In versions of glibc up to and including glibc 2.4, the return type of readlink() was  declared  as  int.
       Nowadays, the return type is declared as ssize_t, as (newly) required in POSIX.1-2001.

       Using  a  statically  sized  buffer  might  not  provide enough room for the symbolic link contents.  The
       required size for the buffer can be obtained from the stat.st_size value returned by a call  to  lstat(2)
       on  the link.  However, the number of bytes written by readlink() should be checked to make sure that the
       size of the symbolic link did not increase between the calls.   Dynamically  allocating  the  buffer  for
       readlink()  also  addresses a common portability problem when using PATH_MAX for the buffer size, as this
       constant is not guaranteed to be defined per POSIX if the system does not have such limit.

EXAMPLE

       The following program allocates the buffer needed by readlink() dynamically from the information provided
       by lstat(), making sure there's no race condition between the calls.

       #include <sys/types.h>
       #include <sys/stat.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>

       int
       main(int argc, char *argv[])
       {
           struct stat sb;
           char *linkname;
           ssize_t r;

           if (argc != 2) {
               fprintf(stderr, "Usage: %s <pathname>\n", argv[0]);
               exit(EXIT_FAILURE);
           }

           if (lstat(argv[1], &sb) == -1) {
               perror("lstat");
               exit(EXIT_FAILURE);
           }

           linkname = malloc(sb.st_size + 1);
           if (linkname == NULL) {
               fprintf(stderr, "insufficient memory\n");
               exit(EXIT_FAILURE);
           }

           r = readlink(argv[1], linkname, sb.st_size + 1);

           if (r == -1) {
               perror("lstat");
               exit(EXIT_FAILURE);
           }

           if (r > sb.st_size) {
               fprintf(stderr, "symlink increased in size "
                               "between lstat() and readlink()\n");
               exit(EXIT_FAILURE);
           }

           linkname[r] = '\0';

           printf("'%s' points to '%s'\n", argv[1], linkname);

           exit(EXIT_SUCCESS);
       }

SEE ALSO

       readlink(1), lstat(2), readlinkat(2), stat(2), symlink(2), path_resolution(7), symlink(7)

COLOPHON

       This page is part of release 3.54 of the Linux man-pages project.  A  description  of  the  project,  and
       information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.

Linux                                              2013-07-18                                        READLINK(2)