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       readlink, readlinkat - read value of a symbolic link


       #include <unistd.h>

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

       #include <fcntl.h>           /* Definition of AT_* constants */
       #include <unistd.h>

       ssize_t readlinkat(int dirfd, const char *pathname,
                          char *buf, size_t bufsiz);

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

           _POSIX_C_SOURCE >= 200112L

           Since glibc 2.10:
               _XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L
           Before glibc 2.10:


       readlink() places the contents of the symbolic link pathname 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.

       The  readlinkat()  system  call operates in exactly the same way as readlink(), except for
       the differences described here.

       If the pathname given in pathname is relative, then it  is  interpreted  relative  to  the
       directory  referred  to  by the file descriptor dirfd (rather than relative to the current
       working directory of the calling  process,  as  is  done  by  readlink()  for  a  relative

       If  pathname  is  relative  and  dirfd  is  the  special  value AT_FDCWD, then pathname is
       interpreted relative to the  current  working  directory  of  the  calling  process  (like

       If pathname is absolute, then dirfd is ignored.

       Since  Linux  2.6.39,  pathname can be an empty string, in which case the call operates on
       the symbolic link referred to by dirfd (which should have been obtained using open(2) with
       the O_PATH and O_NOFOLLOW flags).

       See openat(2) for an explanation of the need for readlinkat().


       On  success,  these  calls  return  the  number  of  bytes placed in buf.  On error, -1 is
       returned and errno is set to indicate the error.


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

       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.

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

       ENOENT The named file does not exist.

       ENOMEM Insufficient kernel memory was available.

              A component of the path prefix is not a directory.

       The following additional errors can occur for readlinkat():

       EBADF  dirfd is not a valid file descriptor.

              pathname  is relative and dirfd is a file descriptor referring to a file other than
              a directory.


       readlinkat() was added to Linux in kernel 2.6.16; library support was added  to  glibc  in
       version 2.4.


       readlink(): 4.4BSD (readlink() first appeared in 4.2BSD), POSIX.1-2001, POSIX.1-2008.

       readlinkat(): POSIX.1-2008.


       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

       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() and readlinkat() 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()
       and readlinkat() 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.

   Glibc notes
       On older kernels where readlinkat() is unavailable, the glibc wrapper function falls  back
       to  the  use  of  readlink().   When  pathname  is a relative pathname, glibc constructs a
       pathname based on the symbolic  link  in  /proc/self/fd  that  corresponds  to  the  dirfd


       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>

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

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

           if (lstat(argv[1], &sb) == -1) {

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

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

           if (r == -1) {

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

           linkname[r] = '\0';

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




       readlink(1), lstat(2), stat(2), symlink(2), realpath(3), path_resolution(7), symlink(7)


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