--- name: "readlink" section: "2" platform: "linux" package: "man-pages" version: "6.19-1" release: "Arch Linux 2026-11-01" platforms: ["linux", "freebsd", "macos"] url: "https://new.carta.tech/readlink/2" --- # readlink(2) read value of a symbolic link ## NAME readlink, readlinkat - read value of a symbolic link ## LIBRARY Standard C library (*libc*, *-lc*) ## SYNOPSIS ``` #include ``` **ssize\_t readlink(**size\_t bufsiz; **const char \*restrict** *path***,** **char** *buf***\[restrict** *bufsiz***\], size\_t** *bufsiz***);** **#include \** /\* Definition of **AT\_\*** constants \*/ **#include \** **ssize\_t readlinkat(**size\_t bufsiz; **int** *dirfd***, const char \*restrict** *path***,** **char** *buf***\[restrict** *bufsiz***\], size\_t** *bufsiz***);** Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)): **readlink**(): ``` _XOPEN_SOURCE >= 500 || _POSIX_C_SOURCE >= 200112L || /* glibc <= 2.19: */ _BSD_SOURCE ``` **readlinkat**(): ``` Since glibc 2.10: _POSIX_C_SOURCE >= 200809L Before glibc 2.10: _ATFILE_SOURCE ``` ## DESCRIPTION **readlink**() places the contents of the symbolic link *path* in the buffer *buf*, which has size *bufsiz*. **readlink**() does not append a terminating null byte to *buf*. It will (silently) truncate the contents (to a length of *bufsiz* characters), in case the buffer is too small to hold all of the contents. ### readlinkat() The **readlinkat**() system call operates in exactly the same way as **readlink**(), except for the differences described here. If *path* 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 *path* is relative and *dirfd* is the special value **AT\_FDCWD**, then *path* is interpreted relative to the current working directory of the calling process (like **readlink**()). If *path* is absolute, then *dirfd* is ignored. Since Linux 2.6.39, *path* 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)](/open/2.md) with the **O\_PATH** and **O\_NOFOLLOW** flags). See [**openat**(2)](/openat/2.md) for an explanation of the need for **readlinkat**(). ## RETURN VALUE On success, these calls return the number of bytes placed in *buf*. (If the returned value equals *bufsiz*, then truncation may have occurred.) 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)](/path_resolution/7.md).) - **EBADF** (**readlinkat**()) *path* is relative but *dirfd* is neither **AT\_FDCWD** nor a valid file descriptor. - **EFAULT** *buf* extends outside the process's allocated address space. - **EINVAL** *bufsiz* is not positive. - **EINVAL** The named file (i.e., the final filename component of *path*) 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. - **ENOTDIR** (**readlinkat**()) *path* is relative and *dirfd* is a file descriptor referring to a file other than a directory. ## STANDARDS POSIX.1-2024. ## HISTORY - **readlink**() 4\.4BSD (first appeared in 4.2BSD), POSIX.1-2001, POSIX.1-2008. - **readlinkat**() POSIX.1-2008. Linux 2.6.16, glibc 2.4. 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. ### glibc On older kernels where **readlinkat**() is unavailable, the glibc wrapper function falls back to the use of **readlink**(). When *path* is relative, glibc constructs a pathname based on the symbolic link in */proc/self/fd* that corresponds to the *dirfd* argument. ## NOTES 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)](/lstat/2.md) 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. ## EXAMPLES The following program allocates the buffer needed by **readlink**() dynamically from the information provided by [**lstat**(2)](/lstat/2.md), falling back to a buffer of size **PATH\_MAX** in cases where [**lstat**(2)](/lstat/2.md) reports a size of zero. ``` #include #include #include #include #include #include int main(int argc, char *argv[]) { char *buf; ssize_t nbytes, bufsiz; struct stat sb; if (argc != 2) { fprintf(stderr, "Usage: %s \n", argv[0]); exit(EXIT_FAILURE); } if (lstat(argv[1], &sb) == -1) { perror("lstat"); exit(EXIT_FAILURE); } /* Add one to the link size, so that we can determine whether the buffer returned by readlink() was truncated. */ bufsiz = sb.st_size + 1; /* Some magic symlinks under (for example) /proc and /sys report 'st_size' as zero. In that case, take PATH_MAX as a "good enough" estimate. */ if (sb.st_size == 0) bufsiz = PATH_MAX; buf = malloc(bufsiz); if (buf == NULL) { perror("malloc"); exit(EXIT_FAILURE); } nbytes = readlink(argv[1], buf, bufsiz); if (nbytes == -1) { perror("readlink"); exit(EXIT_FAILURE); } /* Print only 'nbytes' of 'buf', as it doesn't contain a terminating null byte ('\0'). */ printf("'%s' points to '%.*s'\n", argv[1], (int) nbytes, buf); /* If the return value was equal to the buffer size, then the link target was larger than expected (perhaps because the target was changed between the call to lstat() and the call to readlink()). Warn the user that the returned target may have been truncated. */ if (nbytes == bufsiz) printf("(Returned buffer may have been truncated)\n"); free(buf); exit(EXIT_SUCCESS); } ``` ## SEE ALSO [**readlink**(1)](/readlink/1.md), [**lstat**(2)](/lstat/2.md), [**stat**(2)](/stat/2.md), [**symlink**(2)](/symlink/2.md), [**realpath**(3)](/realpath/3.md), [**path\_resolution**(7)](/path_resolution/7.md), [**symlink**(7)](/symlink/7.md)