-.\" (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
+.\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
.\"
+.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
-.\" License.
+.\" %%%LICENSE_END
+.\"
.\" Modified Wed Jul 21 22:35:42 1993 by Rik Faith (faith@cs.unc.edu)
.\" Modified 18 Mar 1996 by Martin Schulze (joey@infodrom.north.de):
.\" Corrected description of getwd().
.\" Modified Mon Dec 11 13:32:51 MET 2000 by aeb
.\" Modified Thu Apr 22 03:49:15 CEST 2002 by Roger Luethi <rl@hellgate.ch>
.\"
-.TH GETCWD 3 2007-07-26 "GNU" "Linux Programmer's Manual"
+.TH GETCWD 3 2018-04-30 "GNU" "Linux Programmer's Manual"
.SH NAME
-getcwd, getwd, get_current_dir_name \- Get current working directory
+getcwd, getwd, get_current_dir_name \- get current working directory
.SH SYNOPSIS
.nf
.B #include <unistd.h>
-.sp
+.PP
.BI "char *getcwd(char *" buf ", size_t " size );
-.sp
+.PP
.BI "char *getwd(char *" buf );
-.sp
+.PP
.B "char *get_current_dir_name(void);"
.fi
-.sp
+.PP
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
-.sp
-.BR getcwd ():
-_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
-.br
+.PP
.BR get_current_dir_name ():
+.RS
_GNU_SOURCE
+.RE
+.PP
+.BR getwd ():
+.ad l
+.RS 4
+.PD 0
+.TP 4
+Since glibc 2.12:
+.nf
+(_XOPEN_SOURCE\ >=\ 500) && ! (_POSIX_C_SOURCE\ >=\ 200809L)
+ || /* Glibc since 2.19: */ _DEFAULT_SOURCE
+ || /* Glibc versions <= 2.19: */ _BSD_SOURCE
+.TP 4
+.fi
+Before glibc 2.12:
+_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
+.\" || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
+.PD
+.RE
+.ad b
.SH 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
+.IR buf ,
+if present.
+.PP
The
.BR getcwd ()
function copies an absolute pathname of the current working directory
which is of length
.IR size .
.PP
-If the current absolute pathname would require a buffer longer than
+If the length of the absolute pathname of the current working directory,
+including the terminating null byte, exceeds
.I size
-elements, NULL is returned, and
+bytes, NULL is returned, and
.I errno
is set to
.BR ERANGE ;
an application should check for this error, and allocate a larger
buffer if necessary.
.PP
-If
-.I buf
-is NULL, the behavior of
-.BR getcwd ()
-is undefined.
-.PP
-As an extension to the POSIX.1-2001 standard, Linux (libc4, libc5, glibc)
+As an extension to the POSIX.1-2001 standard, glibc's
.BR getcwd ()
allocates the buffer dynamically using
.BR malloc (3)
if
.I buf
-is NULL on call.
+is NULL.
In this case, the allocated buffer has the length
.I size
unless
is zero, when
.I buf
is allocated as big as necessary.
-It is possible (and, indeed,
-advisable) to
+The caller should
.BR free (3)
-the buffers if they have been obtained this way.
-
-.BR get_current_dir_name (),
+the returned buffer.
+.PP
+.BR get_current_dir_name ()
will
.BR malloc (3)
-an array big enough to hold the current directory name.
+an array big enough to hold the absolute pathname of
+the current working directory.
If the environment
variable
.B PWD
is set, and its value is correct, then that value will be returned.
-
-.BR getwd (),
+The caller should
+.BR free (3)
+the returned buffer.
+.PP
+.BR getwd ()
does not
.BR malloc (3)
any memory.
argument should be a pointer to an array at least
.B PATH_MAX
bytes long.
-.BR getwd ()
-does only return the first
+If the length of the absolute pathname of the current working directory,
+including the terminating null byte, exceeds
.B PATH_MAX
-bytes of the actual pathname.
-Note that
+bytes, NULL is returned, and
+.I errno
+is set to
+.BR ENAMETOOLONG .
+(Note that on some systems,
.B PATH_MAX
-need not be a compile-time constant; it may depend on the file system
-and may even be unlimited.
+may not be a compile-time constant;
+furthermore, its value may depend on the filesystem, see
+.BR pathconf (3).)
For portability and security reasons, use of
.BR getwd ()
is deprecated.
-.SH "RETURN VALUE"
-NULL
-on failure with
+.SH RETURN VALUE
+On success, these functions return a pointer to a string containing
+the pathname of the current working directory.
+In the case
+.BR getcwd ()
+and
+.BR getwd ()
+this is the same value as
+.IR buf .
+.PP
+On failure, these functions return NULL, and
.I errno
-set accordingly, and
-.I buf
-on success.
+is set to indicate the error.
The contents of the array pointed to by
.I buf
-is undefined on error.
+are undefined on error.
.SH ERRORS
.TP
.B EACCES
.I buf
is not a null pointer.
.TP
+.B EINVAL
+.BR getwd ():
+.I buf
+is NULL.
+.TP
+.B ENAMETOOLONG
+.BR getwd ():
+The size of the null-terminated absolute pathname string exceeds
+.B PATH_MAX
+bytes.
+.TP
.B ENOENT
The current working directory has been unlinked.
.TP
+.B ENOMEM
+Out of memory.
+.TP
.B ERANGE
The
.I size
-argument is less than the length of the working directory name.
+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.
-.SH "CONFORMING TO"
+.SH ATTRIBUTES
+For an explanation of the terms used in this section, see
+.BR attributes (7).
+.TS
+allbox;
+lbw22 lb lb
+l l l.
+Interface Attribute Value
+T{
+.BR getcwd (),
+.BR getwd ()
+T} Thread safety MT-Safe
+T{
+.BR get_current_dir_name ()
+T} Thread safety MT-Safe env
+.TE
+.SH CONFORMING TO
.BR getcwd ()
conforms to POSIX.1-2001.
+Note however that POSIX.1-2001 leaves the behavior of
+.BR getcwd ()
+unspecified if
+.I buf
+is NULL.
+.PP
.BR getwd ()
is present in POSIX.1-2001, but marked LEGACY.
+POSIX.1-2008 removes the specification of
+.BR getwd ().
+Use
+.BR getcwd ()
+instead.
+POSIX.1-2001
+does not define any errors for
+.BR getwd ().
+.PP
.BR get_current_dir_name ()
is a GNU extension.
.SH NOTES
-Under Linux, the function
+Under Linux, these functions make use of the
.BR getcwd ()
-is a system call (since 2.1.92).
-On older systems it would query
+system call (available since Linux 2.1.92).
+On older systems they would query
.IR /proc/self/cwd .
-If both system call and proc file system are missing, a
+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
.BR EACCES .
-.LP
+.PP
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
.BR 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.
-.SH "SEE ALSO"
+.\"
+.SS C library/kernel differences
+On Linux, the kernel provides a
+.BR 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
+.BR PATH_MAX
+bytes.
+(Before Linux 3.12,
+.\" commit 3272c544da48f8915a0e34189182aed029bd0f2b
+the limit on the size of the returned pathname was the system page size.
+On many architectures,
+.BR 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
+.BR ENAMETOOLONG .
+In this case, the library functions fall back to
+a (slower) alternative implementation that returns the full pathname.
+.PP
+Following a change in Linux 2.6.36,
+.\" commit 8df9d1a4142311c084ffeeacb67cd34d190eff74
+the pathname returned by the
+.BR 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
+.BR 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.
+.SH BUGS
+Since the Linux 2.6.36 change that added "(unreachable)" in the
+circumstances described above, the glibc implementation of
+.BR 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
+.BR getcwd ()
+from such a pathname will now result in failure with
+.BR ENOENT .
+.SH SEE ALSO
+.BR pwd (1),
.BR chdir (2),
.BR fchdir (2),
.BR open (2),
projects / thirdparty / man-pages.git / blobdiff