.\" 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 2016-03-15 "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
.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)):
-.sp
.in
+.PP
.BR get_current_dir_name ():
.RS
_GNU_SOURCE
.RE
-.sp
+.PP
.BR getwd ():
.ad l
.RS 4
The pathname is returned as the function result and via the argument
.IR buf ,
if present.
-
-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),
-then, since Linux 2.6.36,
-.\" commit 8df9d1a4142311c084ffeeacb67cd34d190eff74
-the returned path will be prefixed with the string "(unreachable)".
-Such behavior can also be caused by an unprivileged user by changing
-the current directory into another mount namespace.
-When dealing with paths from untrusted sources, callers of these
-functions should consider checking whether the returned path starts
-with '/' or '(' to avoid misinterpreting an unreachable path
-as a relative path.
-
+.PP
The
.BR getcwd ()
function copies an absolute pathname of the current working directory
The caller should
.BR free (3)
the returned buffer.
-
+.PP
.BR get_current_dir_name ()
will
.BR malloc (3)
The caller should
.BR free (3)
the returned buffer.
-
+.PP
.BR getwd ()
does not
.BR malloc (3)
.BR getwd ()
this is the same value as
.IR buf .
-
+.PP
On failure, these functions return NULL, and
.I errno
is set to indicate the error.
.B PATH_MAX
bytes.
.TP
-.B ENOMEM
-Out of memory.
-.TP
.B ENOENT
The current working directory has been unlinked.
.TP
+.B ENOMEM
+Out of memory.
+.TP
.B ERANGE
The
.I size
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
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 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.
+.\"
+.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),
projects / thirdparty / man-pages.git / blobdiff