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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON |
GETCWD(3) Linux Programmer's Manual GETCWD(3)
getcwd, getwd, get_current_dir_name - get current working directory
#include <unistd.h>
char *getcwd(char *buf, size_t size);
char *getwd(char *buf);
char *get_current_dir_name(void);
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 since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE
Before glibc 2.12:
_BSD_SOURCE || _XOPEN_SOURCE >= 500
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 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) 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) the returned buffer.
get_current_dir_name() will malloc(3) 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) the returned
buffer.
getwd() does not malloc(3) 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 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).) For portability and security
reasons, use of getwd() is deprecated.
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 is set to indicate
the error. The contents of the array pointed to by buf are undefined
on error.
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.
For an explanation of the terms used in this section, see
attributes(7).
┌───────────────────────┬───────────────┬─────────────┐
│Interface │ Attribute │ Value │
├───────────────────────┼───────────────┼─────────────┤
│getcwd(), getwd() │ Thread safety │ MT-Safe │
├───────────────────────┼───────────────┼─────────────┤
│get_current_dir_name() │ Thread safety │ MT-Safe env │
└───────────────────────┴───────────────┴─────────────┘
getcwd() conforms to POSIX.1-2001. Note however that POSIX.1-2001
leaves the behavior of getcwd() unspecified if buf is NULL.
getwd() is present in POSIX.1-2001, but marked LEGACY. POSIX.1-2008
removes the specification of getwd(). Use getcwd() instead.
POSIX.1-2001 does not define any errors for getwd().
get_current_dir_name() is a GNU extension.
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.
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) to return is
usually a faster and more reliable alternative when sufficiently many
file descriptors are available, especially on platforms other than
Linux.
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) 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.
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.
pwd(1), chdir(2), fchdir(2), open(2), unlink(2), free(3), malloc(3)
This page is part of release 5.08 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/.
GNU 2018-04-30 GETCWD(3)
Pages that refer to this page: pwd(1) , chdir(2) , fchdir(2) , realpath(3)
Copyright and license for this manual page