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getcwd(3)
GETCWD(3) Linux Programmer's Manual GETCWD(3)
NAME
getcwd, getwd, get_current_dir_name - get current working directory
SYNOPSIS
#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
DESCRIPTION
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 work‐
ing directory to the array pointed to by buf, which is of length size.
If the length of the absolute pathname of the current working direc‐
tory, 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() allo‐
cates 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 ter‐
minating 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.
RETURN VALUE
On success, these functions return a pointer to a string containing the
pathname of the current working directory. In the case 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.
ERRORS
EACCES Permission to read or search a component of the filename was de‐
nied.
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 path‐
name of the working directory, including the terminating null
byte. You need to allocate a bigger array and try again.
ATTRIBUTES
For an explanation of the terms used in this section, see attrib‐
utes(7). allbox; lbw22 lb lb l l l. Interface Attribute Value T{
getcwd(), getwd() T} Thread safety MT-Safe T{ get_current_dir_name()
T} Thread safety MT-Safe env
CONFORMING TO
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.
NOTES
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 de‐
scriptors are available, especially on platforms other than Linux.
C library/kernel differences
On Linux, the kernel provides a getcwd() system call, which the func‐
tions 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 ch‐
root(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 rela‐
tive pathname.
BUGS
Since the Linux 2.6.36 change that added "(unreachable)" in the circum‐
stances 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 re‐
sult in failure with ENOENT.
SEE ALSO
pwd(1), chdir(2), fchdir(2), open(2), unlink(2), free(3), malloc(3)
COLOPHON
This page is part of release 5.02 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)