getcwd(3) Library Functions Manual getcwd(3)
NAME
getcwd, getwd, get_current_dir_name - get current working directory
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#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 >= 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 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 buf‐
fer 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 neces‐
sary. 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.
RETURN VALUE
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.
ERRORS
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 terminat‐
ing null byte. You need to allocate a bigger array and try again.
ATTRIBUTES
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 │
└─────────────────────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────────┘
STANDARDS
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() in‐
stead. 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 lat‐
er. 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 "(un‐
reachable)" 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 path‐
name starts with '/' or '(' to avoid misinterpreting an unreachable path as a relative pathname.
BUGS
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 path‐
name. With glibc 2.27 onwards this is corrected; calling getcwd() from such a pathname will now result in failure with
ENOENT.
SEE ALSO
pwd(1), chdir(2), fchdir(2), open(2), unlink(2), free(3), malloc(3)
Linux man-pages 6.03 2023-02-05 getcwd(3)