getcwd(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON

GETCWD(3)               Linux Programmer's Manual              GETCWD(3)

NAME         top

       getcwd, getwd, get_current_dir_name - get current working
       directory

SYNOPSIS         top

       #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 <= 2.19: */ _BSD_SOURCE
           Before glibc 2.12:
               _BSD_SOURCE || _XOPEN_SOURCE >= 500

DESCRIPTION         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 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.

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 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).

       ┌──────────────────────────────────┬───────────────┬─────────────┐
       │Interface                         Attribute     Value       │
       ├──────────────────────────────────┼───────────────┼─────────────┤
       │getcwd(), getwd()                 │ Thread safety │ MT-Safe     │
       ├──────────────────────────────────┼───────────────┼─────────────┤
       │get_current_dir_name()            │ Thread safety │ MT-Safe env │
       └──────────────────────────────────┴───────────────┴─────────────┘

CONFORMING TO         top

       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         top

       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.

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), chdir(2), fchdir(2), open(2), unlink(2), free(3),
       malloc(3)

COLOPHON         top

       This page is part of release 5.12 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                            2021-03-22                      GETCWD(3)

Pages that refer to this page: pwd(1)chdir(2)syscalls(2)realpath(3)core(5)