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    Command:

    readlinkat

    
    
    

    SYNOPSIS

           #include <unistd.h>
    
           ssize_t readlink(const char *pathname, char *buf, size_t bufsiz);
    
           #include <fcntl.h>           /* Definition of AT_* constants */
           #include <unistd.h>
    
           int readlinkat(int dirfd, const char *pathname,
                          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
    
           readlinkat():
               Since glibc 2.10:
                   _XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L
               Before glibc 2.10:
                   _ATFILE_SOURCE
    
    
    

    DESCRIPTION

           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  con-
           tents.
    
       readlinkat()
           The  readlinkat() system call operates in exactly the same way as read-
           link(), 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 pathname).
    
           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 readlink()).
    
           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 file referred to by dirfd  (which  may  have  been
           obtained using the open(2) O_PATH flag).  In this case, dirfd can refer
           to any type of file, not just a directory.
    
           See openat(2) for an explanation of the need for readlinkat().
    
           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.
    
           The following additional errors can occur for readlinkat():
    
           EBADF  dirfd is not a valid file descriptor.
    
           ENOTDIR
                  pathname is relative and dirfd is a file descriptor referring to
                  a file other than a directory.
    
    
    

    VERSIONS

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

    CONFORMING TO

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

    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() and read-
           linkat() 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  porta-
           bility  problem  when  using PATH_MAX for the buffer size, as this con-
           stant 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() dynami-
               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("readlink");
                   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),  stat(2),  symlink(2), path_resolution(7), sym-
           link(7)
    
    
    

    Linux 2014-02-21 READLINK(2)

    
    
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