realpath - return the canonicalized absolute pathname
char *realpath(const char *restrict path,
char *restrict resolved_path);
_XOPEN_SOURCE >= 500
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc <= 2.19: */ _BSD_SOURCE
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 /../
If resolved_path is specified as NULL, then
realpath() uses malloc(3) 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
If there is no error, realpath() returns a pointer to the
Otherwise, it returns NULL, the contents of the array
resolved_path are undefined, and errno is set to indicate the
For an explanation of the terms used in this section, see attributes(7).
- Read or search permission was denied for a component of the path
- path is NULL. (In glibc versions before 2.3, this error is also
returned if resolved_path is NULL.)
- An I/O error occurred while reading from the filesystem.
- Too many symbolic links were encountered in translating the pathname.
- A component of a pathname exceeded NAME_MAX characters, or an
entire pathname exceeded PATH_MAX characters.
- The named file does not exist.
- Out of memory.
- A component of the path prefix is not a directory.
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) function. A typical source fragment would be
path_max = PATH_MAX;
path_max = pathconf(path, _PC_PATH_MAX);
if (path_max <= 0)
path_max = 4096;
(But see the BUGS section.)
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.
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). And asking
pathconf(3) does not really help, since, on the one hand POSIX warns
that the result of pathconf(3) may be huge and unsuitable for mallocing
memory, and on the other hand pathconf(3) 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.
This page is part of release 5.13 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the latest
version of this page, can be found at https://www.kernel.org/doc/man-pages/.