Ubuntu Manpage: getcwd, getwd, get_current_dir_name

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 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

       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  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 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() 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 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

       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.