getcwd

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 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 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  at-
       tributes(7).

       +-----------------------+---------------+-------------+
       |Interface              | Attribute     | Value       |
       +-----------------------+---------------+-------------+
       |getcwd(), getwd()      | Thread safety | MT-Safe     |
       +-----------------------+---------------+-------------+
       |get_current_dir_name() | 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 5.05 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)