getcwd(3) - Linux manual page (original) (raw)
getcwd(3) Library Functions Manual getcwd(3)
NAME top
getcwd, getwd, get_current_dir_name - get current working
directoryLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#include <unistd.h>**
**char *getcwd(char** _buf_**[.**_size_**], size_t** _size_**);**
**char *get_current_dir_name(void);**
**[[deprecated]] char *getwd(char** _buf_**[PATH_MAX]);**Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
**get_current_dir_name**():
_GNU_SOURCE
**getwd**():
Since glibc 2.12:
(_XOPEN_SOURCE >= 500) && ! (_POSIX_C_SOURCE >= 200809L)
|| /* glibc >= 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE
Before glibc 2.12:
_BSD_SOURCE || _XOPEN_SOURCE >= 500DESCRIPTION top
These functions return a null-terminated string containing an
absolute pathname that is the current working directory of the
calling process. The pathname is returned as the function result
and via the argument _buf_, if present.
The **getcwd**() function copies an absolute pathname of the current
working directory to the array pointed to by _buf_, which is of
length _size_.
If the length of the absolute pathname of the current working
directory, including the terminating null byte, exceeds _size_
bytes, NULL is returned, and _[errno](../man3/errno.3.html)_ is set to **ERANGE**; an
application should check for this error, and allocate a larger
buffer if necessary.
As an extension to the POSIX.1-2001 standard, glibc's **getcwd**()
allocates the buffer dynamically using [malloc(3)](../man3/malloc.3.html) if _buf_ is NULL.
In this case, the allocated buffer has the length _size_ unless _size_
is zero, when _buf_ is allocated as big as necessary. The caller
should [free(3)](../man3/free.3.html) the returned buffer.
**get_current_dir_name**() will [malloc(3)](../man3/malloc.3.html) an array big enough to hold
the absolute pathname of the current working directory. If the
environment variable **PWD** is set, and its value is correct, then
that value will be returned. The caller should [free(3)](../man3/free.3.html) the
returned buffer.
**getwd**() does not [malloc(3)](../man3/malloc.3.html) any memory. The _buf_ argument should be
a pointer to an array at least **PATH_MAX** bytes long. If the length
of the absolute pathname of the current working directory,
including the terminating null byte, exceeds **PATH_MAX** bytes, NULL
is returned, and _[errno](../man3/errno.3.html)_ is set to **ENAMETOOLONG**. (Note that on some
systems, **PATH_MAX** may not be a compile-time constant; furthermore,
its value may depend on the filesystem, see [pathconf(3)](../man3/pathconf.3.html).) For
portability and security reasons, use of **getwd**() is deprecated.RETURN VALUE top
On success, these functions return a pointer to a string
containing the pathname of the current working directory. In the
case of **getcwd**() and **getwd**() this is the same value as _buf_.
On failure, these functions return NULL, and _[errno](../man3/errno.3.html)_ is set to
indicate the error. The contents of the array pointed to by _buf_
are undefined on error.ERRORS top
**EACCES** Permission to read or search a component of the filename
was denied.
**EFAULT** _buf_ points to a bad address.
**EINVAL** The _size_ argument is zero and _buf_ is not a null pointer.
**EINVAL getwd**(): _buf_ is NULL.
**ENAMETOOLONG**
**getwd**(): The size of the null-terminated absolute pathname
string exceeds **PATH_MAX** bytes.
**ENOENT** The current working directory has been unlinked.
**ENOMEM** Out of memory.
**ERANGE** The _size_ argument is less than the length of the absolute
pathname of the working directory, including the
terminating null byte. You need to allocate a bigger array
and try again.ATTRIBUTES top
For an explanation of the terms used in this section, see
[attributes(7)](../man7/attributes.7.html).
┌──────────────────────────────────┬───────────────┬─────────────┐
│ **Interface** │ **Attribute** │ **Value** │
├──────────────────────────────────┼───────────────┼─────────────┤
│ **getcwd**(), **getwd**() │ Thread safety │ MT-Safe │
├──────────────────────────────────┼───────────────┼─────────────┤
│ **get_current_dir_name**() │ Thread safety │ MT-Safe env │
└──────────────────────────────────┴───────────────┴─────────────┘VERSIONS top
POSIX.1-2001 leaves the behavior of **getcwd**() unspecified if _buf_ is
NULL.
POSIX.1-2001 does not define any errors for **getwd**().VERSIONS top
C library/kernel differences On Linux, the kernel provides a getcwd() system call, which the functions described in this page will use if possible. The system call takes the same arguments as the library function of the same name, but is limited to returning at most PATH_MAX bytes. (Before Linux 3.12, the limit on the size of the returned pathname was the system page size. On many architectures, PATH_MAX and the system page size are both 4096 bytes, but a few architectures have a larger page size.) If the length of the pathname of the current working directory exceeds this limit, then the system call fails with the error ENAMETOOLONG. In this case, the library functions fall back to a (slower) alternative implementation that returns the full pathname.
Following a change in Linux 2.6.36, the pathname returned by the
**getcwd**() system call will be prefixed with the string
"(unreachable)" if the current directory is not below the root
directory of the current process (e.g., because the process set a
new filesystem root using [chroot(2)](../man2/chroot.2.html) without changing its current
directory into the new root). Such behavior can also be caused by
an unprivileged user by changing the current directory into
another mount namespace. When dealing with pathname from
untrusted sources, callers of the functions described in this page
should consider checking whether the returned pathname starts with
'/' or '(' to avoid misinterpreting an unreachable path as a
relative pathname.STANDARDS top
**getcwd**()
POSIX.1-2008.
**get_current_dir_name**()
GNU.
**getwd**()
None.HISTORY top
**getcwd**()
POSIX.1-2001.
**getwd**()
POSIX.1-2001, but marked LEGACY. Removed in POSIX.1-2008.
Use **getcwd**() instead.
Under Linux, these functions make use of the **getcwd**() system call
(available since Linux 2.1.92). On older systems they would query
_/proc/self/cwd_. If both system call and proc filesystem are
missing, a generic implementation is called. Only in that case
can these calls fail under Linux with **EACCES**.NOTES top
These functions are often used to save the location of the current
working directory for the purpose of returning to it later.
Opening the current directory (".") and calling [fchdir(2)](../man2/fchdir.2.html) to
return is usually a faster and more reliable alternative when
sufficiently many file descriptors are available, especially on
platforms other than Linux.BUGS top
Since the Linux 2.6.36 change that added "(unreachable)" in the
circumstances described above, the glibc implementation of
**getcwd**() has failed to conform to POSIX and returned a relative
pathname when the API contract requires an absolute pathname.
With glibc 2.27 onwards this is corrected; calling **getcwd**() from
such a pathname will now result in failure with **ENOENT**.SEE ALSO top
[pwd(1)](../man1/pwd.1.html), [chdir(2)](../man2/chdir.2.html), [fchdir(2)](../man2/fchdir.2.html), [open(2)](../man2/open.2.html), [unlink(2)](../man2/unlink.2.html), [free(3)](../man3/free.3.html),
[malloc(3)](../man3/malloc.3.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-07-23 getcwd(3)
Pages that refer to this page:pwd(1), chdir(2), syscalls(2), realpath(3), core(5)