1GETCWD(3) Linux Programmer's Manual GETCWD(3)
2
6 getcwd, getwd, get_current_dir_name - get current working directory
7
9 #include <unistd.h>
10 char *getcwd(char *buf, size_t size);
12 char *getwd(char *buf);
13 char *get_current_dir_name(void);
14 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
16 get_current_dir_name():
18 _GNU_SOURCE
19 getwd():
21 Since glibc 2.12:
22 (_XOPEN_SOURCE >= 500) && ! (_POSIX_C_SOURCE >= 200809L)
23 || /* Glibc since 2.19: */ _DEFAULT_SOURCE
24 || /* Glibc <= 2.19: */ _BSD_SOURCE
25 Before glibc 2.12:
26 _BSD_SOURCE || _XOPEN_SOURCE >= 500
27
29 These functions return a null-terminated string containing an absolute
30 pathname that is the current working directory of the calling process.
31 The pathname is returned as the function result and via the argument
32 buf, if present.
33 The getcwd() function copies an absolute pathname of the current work‐
35 ing directory to the array pointed to by buf, which is of length size.
36 If the length of the absolute pathname of the current working direc‐
38 tory, including the terminating null byte, exceeds size bytes, NULL is
39 returned, and errno is set to ERANGE; an application should check for
40 this error, and allocate a larger buffer if necessary.
41 As an extension to the POSIX.1-2001 standard, glibc's getcwd() allo‐
43 cates the buffer dynamically using malloc(3) if buf is NULL. In this
44 case, the allocated buffer has the length size unless size is zero,
45 when buf is allocated as big as necessary. The caller should free(3)
46 the returned buffer.
47 get_current_dir_name() will malloc(3) an array big enough to hold the
49 absolute pathname of the current working directory. If the environment
50 variable PWD is set, and its value is correct, then that value will be
51 returned. The caller should free(3) the returned buffer.
52 getwd() does not malloc(3) any memory. The buf argument should be a
54 pointer to an array at least PATH_MAX bytes long. If the length of the
55 absolute pathname of the current working directory, including the ter‐
56 minating null byte, exceeds PATH_MAX bytes, NULL is returned, and errno
57 is set to ENAMETOOLONG. (Note that on some systems, PATH_MAX may not
58 be a compile-time constant; furthermore, its value may depend on the
59 filesystem, see pathconf(3).) For portability and security reasons,
60 use of getwd() is deprecated.
61
63 On success, these functions return a pointer to a string containing the
64 pathname of the current working directory. In the case of getcwd() and
65 getwd() this is the same value as buf.
66 On failure, these functions return NULL, and errno is set to indicate
68 the error. The contents of the array pointed to by buf are undefined
69 on error.
70
72 EACCES Permission to read or search a component of the filename was de‐
73 nied.
74 EFAULT buf points to a bad address.
76 EINVAL The size argument is zero and buf is not a null pointer.
78 EINVAL getwd(): buf is NULL.
80 ENAMETOOLONG
82 getwd(): The size of the null-terminated absolute pathname
83 string exceeds PATH_MAX bytes.
84 ENOENT The current working directory has been unlinked.
86 ENOMEM Out of memory.
88 ERANGE The size argument is less than the length of the absolute path‐
90 name of the working directory, including the terminating null
91 byte. You need to allocate a bigger array and try again.
92
94 For an explanation of the terms used in this section, see at‐
95 tributes(7).
96 ┌────────────────────────────────────────┬───────────────┬─────────────┐
98 │Interface │ Attribute │ Value │
99 ├────────────────────────────────────────┼───────────────┼─────────────┤
100 │getcwd(), getwd() │ Thread safety │ MT-Safe │
101 ├────────────────────────────────────────┼───────────────┼─────────────┤
102 │get_current_dir_name() │ Thread safety │ MT-Safe env │
103 └────────────────────────────────────────┴───────────────┴─────────────┘
104
106 getcwd() conforms to POSIX.1-2001. Note however that POSIX.1-2001
107 leaves the behavior of getcwd() unspecified if buf is NULL.
108 getwd() is present in POSIX.1-2001, but marked LEGACY. POSIX.1-2008
110 removes the specification of getwd(). Use getcwd() instead.
111 POSIX.1-2001 does not define any errors for getwd().
112 get_current_dir_name() is a GNU extension.
114
116 Under Linux, these functions make use of the getcwd() system call
117 (available since Linux 2.1.92). On older systems they would query
118 /proc/self/cwd. If both system call and proc filesystem are missing, a
119 generic implementation is called. Only in that case can these calls
120 fail under Linux with EACCES.
121 These functions are often used to save the location of the current
123 working directory for the purpose of returning to it later. Opening
124 the current directory (".") and calling fchdir(2) to return is usually
125 a faster and more reliable alternative when sufficiently many file de‐
126 scriptors are available, especially on platforms other than Linux.
127 C library/kernel differences
129 On Linux, the kernel provides a getcwd() system call, which the func‐
130 tions described in this page will use if possible. The system call
131 takes the same arguments as the library function of the same name, but
132 is limited to returning at most PATH_MAX bytes. (Before Linux 3.12,
133 the limit on the size of the returned pathname was the system page
134 size. On many architectures, PATH_MAX and the system page size are
135 both 4096 bytes, but a few architectures have a larger page size.) If
136 the length of the pathname of the current working directory exceeds
137 this limit, then the system call fails with the error ENAMETOOLONG. In
138 this case, the library functions fall back to a (slower) alternative
139 implementation that returns the full pathname.
140 Following a change in Linux 2.6.36, the pathname returned by the
142 getcwd() system call will be prefixed with the string "(unreachable)"
143 if the current directory is not below the root directory of the current
144 process (e.g., because the process set a new filesystem root using ch‐
145 root(2) without changing its current directory into the new root).
146 Such behavior can also be caused by an unprivileged user by changing
147 the current directory into another mount namespace. When dealing with
148 pathname from untrusted sources, callers of the functions described in
149 this page should consider checking whether the returned pathname starts
150 with '/' or '(' to avoid misinterpreting an unreachable path as a rela‐
151 tive pathname.
152
154 Since the Linux 2.6.36 change that added "(unreachable)" in the circum‐
155 stances described above, the glibc implementation of getcwd() has
156 failed to conform to POSIX and returned a relative pathname when the
157 API contract requires an absolute pathname. With glibc 2.27 onwards
158 this is corrected; calling getcwd() from such a pathname will now re‐
159 sult in failure with ENOENT.
160
162 pwd(1), chdir(2), fchdir(2), open(2), unlink(2), free(3), malloc(3)
163
165 This page is part of release 5.12 of the Linux man-pages project. A
166 description of the project, information about reporting bugs, and the
167 latest version of this page, can be found at
168 https://www.kernel.org/doc/man-pages/.
169GNU 2021-03-22 GETCWD(3)