man3/getcwd.3

   1 .\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
   2 .\"
   3 .\" %%%LICENSE_START(VERBATIM)
   4 .\" Permission is granted to make and distribute verbatim copies of this
   5 .\" manual provided the copyright notice and this permission notice are
   6 .\" preserved on all copies.
   7 .\"
   8 .\" Permission is granted to copy and distribute modified versions of this
   9 .\" manual under the conditions for verbatim copying, provided that the
  10 .\" entire resulting derived work is distributed under the terms of a
  11 .\" permission notice identical to this one.
  12 .\"
  13 .\" Since the Linux kernel and libraries are constantly changing, this
  14 .\" manual page may be incorrect or out-of-date.  The author(s) assume no
  15 .\" responsibility for errors or omissions, or for damages resulting from
  16 .\" the use of the information contained herein.  The author(s) may not
  17 .\" have taken the same level of care in the production of this manual,
  18 .\" which is licensed free of charge, as they might when working
  19 .\" professionally.
  20 .\"
  21 .\" Formatted or processed versions of this manual, if unaccompanied by
  22 .\" the source, must acknowledge the copyright and authors of this work.
  23 .\" %%%LICENSE_END
  24 .\"
  25 .\" Modified Wed Jul 21 22:35:42 1993 by Rik Faith (faith@cs.unc.edu)
  26 .\" Modified 18 Mar 1996 by Martin Schulze (joey@infodrom.north.de):
  27 .\"   Corrected description of getwd().
  28 .\" Modified Sat Aug 21 12:32:12 MET 1999 by aeb - applied fix by aj
  29 .\" Modified Mon Dec 11 13:32:51 MET 2000 by aeb
  30 .\" Modified Thu Apr 22 03:49:15 CEST 2002 by Roger Luethi <rl@hellgate.ch>
  31 .\"
  32 .TH GETCWD 3 2018-04-30 "GNU" "Linux Programmer's Manual"
  33 .SH NAME
  34 getcwd, getwd, get_current_dir_name \- get current working directory
  35 .SH SYNOPSIS
  36 .nf
  37 .B #include <unistd.h>
  38 .PP
  39 .BI "char *getcwd(char *" buf ", size_t " size );
  40 .PP
  41 .BI "char *getwd(char *" buf );
  42 .PP
  43 .B "char *get_current_dir_name(void);"
  44 .fi
  45 .PP
  46 .in -4n
  47 Feature Test Macro Requirements for glibc (see
  48 .BR feature_test_macros (7)):
  49 .in
  50 .PP
  51 .BR get_current_dir_name ():
  52 .RS
  53 _GNU_SOURCE
  54 .RE
  55 .PP
  56 .BR getwd ():
  57 .ad l
  58 .RS 4
  59 .PD 0
  60 .TP 4
  61 Since glibc 2.12:
  62 .nf
  63 (_XOPEN_SOURCE\ >=\ 500) && ! (_POSIX_C_SOURCE\ >=\ 200809L)
  64     || /* Glibc since 2.19: */ _DEFAULT_SOURCE
  65     || /* Glibc versions <= 2.19: */ _BSD_SOURCE
  66 .TP 4
  67 .fi
  68 Before glibc 2.12:
  69 _BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
  70 .\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
  71 .PD
  72 .RE
  73 .ad b
  74 .SH DESCRIPTION
  75 These functions return a null-terminated string containing an
  76 absolute pathname that is the current working directory of
  77 the calling process.
  78 The pathname is returned as the function result and via the argument
  79 .IR buf ,
  80 if present.
  81 .PP
  82 The
  83 .BR getcwd ()
  84 function copies an absolute pathname of the current working directory
  85 to the array pointed to by
  86 .IR buf ,
  87 which is of length
  88 .IR size .
  89 .PP
  90 If the length of the absolute pathname of the current working directory,
  91 including the terminating null byte, exceeds
  92 .I size
  93 bytes, NULL is returned, and
  94 .I errno
  95 is set to
  96 .BR ERANGE ;
  97 an application should check for this error, and allocate a larger
  98 buffer if necessary.
  99 .PP
 100 As an extension to the POSIX.1-2001 standard, glibc's
 101 .BR getcwd ()
 102 allocates the buffer dynamically using
 103 .BR malloc (3)
 104 if
 105 .I buf
 106 is NULL.
 107 In this case, the allocated buffer has the length
 108 .I size
 109 unless
 110 .I size
 111 is zero, when
 112 .I buf
 113 is allocated as big as necessary.
 114 The caller should
 115 .BR free (3)
 116 the returned buffer.
 117 .PP
 118 .BR get_current_dir_name ()
 119 will
 120 .BR malloc (3)
 121 an array big enough to hold the absolute pathname of
 122 the current working directory.
 123 If the environment
 124 variable
 125 .B PWD
 126 is set, and its value is correct, then that value will be returned.
 127 The caller should
 128 .BR free (3)
 129 the returned buffer.
 130 .PP
 131 .BR getwd ()
 132 does not
 133 .BR malloc (3)
 134 any memory.
 135 The
 136 .I buf
 137 argument should be a pointer to an array at least
 138 .B PATH_MAX
 139 bytes long.
 140 If the length of the absolute pathname of the current working directory,
 141 including the terminating null byte, exceeds
 142 .B PATH_MAX
 143 bytes, NULL is returned, and
 144 .I errno
 145 is set to
 146 .BR ENAMETOOLONG .
 147 (Note that on some systems,
 148 .B PATH_MAX
 149 may not be a compile-time constant;
 150 furthermore, its value may depend on the filesystem, see
 151 .BR pathconf (3).)
 152 For portability and security reasons, use of
 153 .BR getwd ()
 154 is deprecated.
 155 .SH RETURN VALUE
 156 On success, these functions return a pointer to a string containing
 157 the pathname of the current working directory.
 158 In the case of
 159 .BR getcwd ()
 160 and
 161 .BR getwd ()
 162 this is the same value as
 163 .IR buf .
 164 .PP
 165 On failure, these functions return NULL, and
 166 .I errno
 167 is set to indicate the error.
 168 The contents of the array pointed to by
 169 .I buf
 170 are undefined on error.
 171 .SH ERRORS
 172 .TP
 173 .B EACCES
 174 Permission to read or search a component of the filename was denied.
 175 .TP
 176 .B EFAULT
 177 .I buf
 178 points to a bad address.
 179 .TP
 180 .B EINVAL
 181 The
 182 .I size
 183 argument is zero and
 184 .I buf
 185 is not a null pointer.
 186 .TP
 187 .B EINVAL
 188 .BR getwd ():
 189 .I buf
 190 is NULL.
 191 .TP
 192 .B ENAMETOOLONG
 193 .BR getwd ():
 194 The size of the null-terminated absolute pathname string exceeds
 195 .B PATH_MAX
 196 bytes.
 197 .TP
 198 .B ENOENT
 199 The current working directory has been unlinked.
 200 .TP
 201 .B ENOMEM
 202 Out of memory.
 203 .TP
 204 .B ERANGE
 205 The
 206 .I size
 207 argument is less than the length of the absolute pathname of the
 208 working directory, including the terminating null byte.
 209 You need to allocate a bigger array and try again.
 210 .SH ATTRIBUTES
 211 For an explanation of the terms used in this section, see
 212 .BR attributes (7).
 213 .TS
 214 allbox;
 215 lbw22 lb lb
 216 l l l.
 217 Interface       Attribute       Value
 218 T{
 219 .BR getcwd (),
 220 .BR getwd ()
 221 T}      Thread safety   MT-Safe
 222 T{
 223 .BR get_current_dir_name ()
 224 T}      Thread safety   MT-Safe env
 225 .TE
 226 .SH CONFORMING TO
 227 .BR getcwd ()
 228 conforms to POSIX.1-2001.
 229 Note however that POSIX.1-2001 leaves the behavior of
 230 .BR getcwd ()
 231 unspecified if
 232 .I buf
 233 is NULL.
 234 .PP
 235 .BR getwd ()
 236 is present in POSIX.1-2001, but marked LEGACY.
 237 POSIX.1-2008 removes the specification of
 238 .BR getwd ().
 239 Use
 240 .BR getcwd ()
 241 instead.
 242 POSIX.1-2001
 243 does not define any errors for
 244 .BR getwd ().
 245 .PP
 246 .BR get_current_dir_name ()
 247 is a GNU extension.
 248 .SH NOTES
 249 Under Linux, these functions make use of the
 250 .BR getcwd ()
 251 system call (available since Linux 2.1.92).
 252 On older systems they would query
 253 .IR /proc/self/cwd .
 254 If both system call and proc filesystem are missing, a
 255 generic implementation is called.
 256 Only in that case can
 257 these calls fail under Linux with
 258 .BR EACCES .
 259 .PP
 260 These functions are often used to save the location of the current working
 261 directory for the purpose of returning to it later.
 262 Opening the current
 263 directory (".") and calling
 264 .BR fchdir (2)
 265 to return is usually a faster and more reliable alternative when sufficiently
 266 many file descriptors are available, especially on platforms other than Linux.
 267 .\"
 268 .SS C library/kernel differences
 269 On Linux, the kernel provides a
 270 .BR getcwd ()
 271 system call, which the functions described in this page will use if possible.
 272 The system call takes the same arguments as the library function
 273 of the same name, but is limited to returning at most
 274 .BR PATH_MAX
 275 bytes.
 276 (Before Linux 3.12,
 277 .\" commit 3272c544da48f8915a0e34189182aed029bd0f2b
 278 the limit on the size of the returned pathname was the system page size.
 279 On many architectures,
 280 .BR PATH_MAX
 281 and the system page size are both 4096 bytes,
 282 but a few architectures have a larger page size.)
 283 If the length of the pathname of the current working directory
 284 exceeds this limit, then the system call fails with the error
 285 .BR ENAMETOOLONG .
 286 In this case, the library functions fall back to
 287 a (slower) alternative implementation that returns the full pathname.
 288 .PP
 289 Following a change in Linux 2.6.36,
 290 .\" commit 8df9d1a4142311c084ffeeacb67cd34d190eff74
 291 the pathname returned by the
 292 .BR getcwd ()
 293 system call will be prefixed with the string "(unreachable)"
 294 if the current directory is not below the root directory of the current
 295 process (e.g., because the process set a new filesystem root using
 296 .BR chroot (2)
 297 without changing its current directory into the new root).
 298 Such behavior can also be caused by an unprivileged user by changing
 299 the current directory into another mount namespace.
 300 When dealing with pathname from untrusted sources, callers of the
 301 functions described in this page
 302 should consider checking whether the returned pathname starts
 303 with '/' or '(' to avoid misinterpreting an unreachable path
 304 as a relative pathname.
 305 .SH BUGS
 306 Since the Linux 2.6.36 change that added "(unreachable)" in the
 307 circumstances described above, the glibc implementation of
 308 .BR getcwd ()
 309 has failed to conform to POSIX and returned a relative pathname when the API
 310 contract requires an absolute pathname.
 311 With glibc 2.27 onwards this is corrected;
 312 calling
 313 .BR getcwd ()
 314 from such a pathname will now result in failure with
 315 .BR ENOENT .
 316 .SH SEE ALSO
 317 .BR pwd (1),
 318 .BR chdir (2),
 319 .BR fchdir (2),
 320 .BR open (2),
 321 .BR unlink (2),
 322 .BR free (3),
 323 .BR malloc (3)