Provided by: manpages-dev_3.35-0.1ubuntu1_all bug

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 file system.

       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 < 0) {
               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[sb.st_size] = '\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 3.35 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://man7.org/linux/man-pages/.