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 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 │
       └───────────────────────┴───────────────┴─────────────┘
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
       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.

SEE ALSO
       pwd(1), chdir(2), fchdir(2), open(2), unlink(2), free(3), malloc(3)

COLOPHON
       This page is part of release 5.09 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)