---
name: "realpath"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/realpath/3"
---

# realpath(3)

return the canonicalized absolute pathname

## NAME

realpath - return the canonicalized absolute pathname

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <limits.h>
#include <stdlib.h>
```

**char \*realpath(const char \*restrict** *path***,**                **char \*restrict** *resolved\_path***);**

Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)):

**realpath**():

```
    _XOPEN_SOURCE >= 500
        || /* glibc >= 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE
```

## DESCRIPTION

**realpath**() expands all symbolic links and resolves references to */./*, */../* and extra '/' characters in the null-terminated string named by *path* to produce a canonicalized absolute pathname. The resulting pathname is stored as a null-terminated string, up to a maximum of **PATH\_MAX** bytes, in the buffer pointed to by *resolved\_path*. The resulting path will have no symbolic link, */./* or */../* components.

If *resolved\_path* is specified as NULL, then **realpath**() uses [**malloc**(3)](/malloc/3.md) to allocate a buffer of up to **PATH\_MAX** bytes to hold the resolved pathname, and returns a pointer to this buffer. The caller should deallocate this buffer using [**free**(3)](/free/3.md).

## RETURN VALUE

If there is no error, **realpath**() returns a pointer to the *resolved\_path*.

Otherwise, it returns NULL, the contents of the array *resolved\_path* are undefined, and *errno* is set to indicate the error.

## ERRORS

- **EACCES**

  Read or search permission was denied for a component of the path prefix.

- **EINVAL**

  *path* is NULL. (Before glibc 2.3, this error is also returned if *resolved\_path* is NULL.)

- **EIO**

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

- **ELOOP**

  Too many symbolic links were encountered in translating the pathname.

- **ENAMETOOLONG**

  A component of a pathname exceeded **NAME\_MAX** characters, or an entire pathname exceeded **PATH\_MAX** characters.

- **ENOENT**

  The named file does not exist.

- **ENOMEM**

  Out of memory.

- **ENOTDIR**

  A component of the path prefix is not a directory.

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **realpath**() | Thread safety | MT-Safe |

## VERSIONS

### GNU extensions

If the call fails with either **EACCES** or **ENOENT** and *resolved\_path* is not NULL, then the prefix of *path* that is not readable or does not exist is returned in *resolved\_path*.

## STANDARDS

POSIX.1-2008.

## HISTORY

4\.4BSD, POSIX.1-2001, Solaris.

POSIX.1-2001 says that the behavior if *resolved\_path* is NULL is implementation-defined. POSIX.1-2008 specifies the behavior described in this page.

In 4.4BSD and Solaris, the limit on the pathname length is **MAXPATHLEN** (found in *\<sys/param.h\>*). SUSv2 prescribes **PATH\_MAX** and **NAME\_MAX**, as found in *\<limits.h\>* or provided by the [**pathconf**(3)](/pathconf/3.md) function. A typical source fragment would be

```
#ifdef PATH_MAX
  path_max = PATH_MAX;
#else
  path_max = pathconf(path, _PC_PATH_MAX);
  if (path_max <= 0)
    path_max = 4096;
#endif
```

(But see the BUGS section.)

## BUGS

The POSIX.1-2001 standard version of this function is broken by design, since it is impossible to determine a suitable size for the output buffer, *resolved\_path*. According to POSIX.1-2001 a buffer of size **PATH\_MAX** suffices, but **PATH\_MAX** need not be a defined constant, and may have to be obtained using [**pathconf**(3)](/pathconf/3.md). And asking [**pathconf**(3)](/pathconf/3.md) does not really help, since, on the one hand POSIX warns that the result of [**pathconf**(3)](/pathconf/3.md) may be huge and unsuitable for mallocing memory, and on the other hand [**pathconf**(3)](/pathconf/3.md) may return -1 to signify that **PATH\_MAX** is not bounded. The *resolved\_path == NULL* feature, not standardized in POSIX.1-2001, but standardized in POSIX.1-2008, allows this design problem to be avoided.

## SEE ALSO

[**realpath**(1)](/realpath/1.md), [**readlink**(2)](/readlink/2.md), [**canonicalize\_file\_name**(3)](/canonicalize_file_name/3.md), [**getcwd**(3)](/getcwd/3.md), [**pathconf**(3)](/pathconf/3.md), [**sysconf**(3)](/sysconf/3.md)