1GETCWD(3) Linux Programmer's Manual GETCWD(3)
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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);
14 char *get_current_dir_name(void);
16 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
18 get_current_dir_name():
20 _GNU_SOURCE
21 getwd():
23 Since glibc 2.12:
24 (_XOPEN_SOURCE >= 500) && ! (_POSIX_C_SOURCE >= 200809L)
25 || /* Glibc since 2.19: */ _DEFAULT_SOURCE
26 || /* Glibc versions <= 2.19: */ _BSD_SOURCE
27 Before glibc 2.12:
28 _BSD_SOURCE || _XOPEN_SOURCE >= 500
29
31 These functions return a null-terminated string containing an absolute
32 pathname that is the current working directory of the calling process.
33 The pathname is returned as the function result and via the argument
34 buf, if present.
35 The getcwd() function copies an absolute pathname of the current work‐
37 ing directory to the array pointed to by buf, which is of length size.
38 If the length of the absolute pathname of the current working direc‐
40 tory, including the terminating null byte, exceeds size bytes, NULL is
41 returned, and errno is set to ERANGE; an application should check for
42 this error, and allocate a larger buffer if necessary.
43 As an extension to the POSIX.1-2001 standard, glibc's getcwd() allo‐
45 cates the buffer dynamically using malloc(3) if buf is NULL. In this
46 case, the allocated buffer has the length size unless size is zero,
47 when buf is allocated as big as necessary. The caller should free(3)
48 the returned buffer.
49 get_current_dir_name() will malloc(3) an array big enough to hold the
51 absolute pathname of the current working directory. If the environment
52 variable PWD is set, and its value is correct, then that value will be
53 returned. The caller should free(3) the returned buffer.
54 getwd() does not malloc(3) any memory. The buf argument should be a
56 pointer to an array at least PATH_MAX bytes long. If the length of the
57 absolute pathname of the current working directory, including the ter‐
58 minating null byte, exceeds PATH_MAX bytes, NULL is returned, and errno
59 is set to ENAMETOOLONG. (Note that on some systems, PATH_MAX may not
60 be a compile-time constant; furthermore, its value may depend on the
61 filesystem, see pathconf(3).) For portability and security reasons,
62 use of getwd() is deprecated.
63
65 On success, these functions return a pointer to a string containing the
66 pathname of the current working directory. In the case getcwd() and
67 getwd() this is the same value as buf.
68 On failure, these functions return NULL, and errno is set to indicate
70 the error. The contents of the array pointed to by buf are undefined
71 on error.
72
74 EACCES Permission to read or search a component of the filename was
75 denied.
76 EFAULT buf points to a bad address.
78 EINVAL The size argument is zero and buf is not a null pointer.
80 EINVAL getwd(): buf is NULL.
82 ENAMETOOLONG
84 getwd(): The size of the null-terminated absolute pathname
85 string exceeds PATH_MAX bytes.
86 ENOENT The current working directory has been unlinked.
88 ENOMEM Out of memory.
90 ERANGE The size argument is less than the length of the absolute path‐
92 name of the working directory, including the terminating null
93 byte. You need to allocate a bigger array and try again.
94
96 For an explanation of the terms used in this section, see
97 attributes(7).
98 ┌───────────────────────┬───────────────┬─────────────┐
100 │Interface │ Attribute │ Value │
101 ├───────────────────────┼───────────────┼─────────────┤
102 │getcwd(), getwd() │ Thread safety │ MT-Safe │
103 ├───────────────────────┼───────────────┼─────────────┤
104 │get_current_dir_name() │ Thread safety │ MT-Safe env │
105 └───────────────────────┴───────────────┴─────────────┘
107 getcwd() conforms to POSIX.1-2001. Note however that POSIX.1-2001
108 leaves the behavior of getcwd() unspecified if buf is NULL.
109 getwd() is present in POSIX.1-2001, but marked LEGACY. POSIX.1-2008
111 removes the specification of getwd(). Use getcwd() instead.
112 POSIX.1-2001 does not define any errors for getwd().
113 get_current_dir_name() is a GNU extension.
115
117 Under Linux, these functions make use of the getcwd() system call
118 (available since Linux 2.1.92). On older systems they would query
119 /proc/self/cwd. If both system call and proc filesystem are missing, a
120 generic implementation is called. Only in that case can these calls
121 fail under Linux with EACCES.
122 These functions are often used to save the location of the current
124 working directory for the purpose of returning to it later. Opening
125 the current directory (".") and calling fchdir(2) to return is usually
126 a faster and more reliable alternative when sufficiently many file
127 descriptors are available, especially on platforms other than Linux.
128 C library/kernel differences
130 On Linux, the kernel provides a getcwd() system call, which the func‐
131 tions described in this page will use if possible. The system call
132 takes the same arguments as the library function of the same name, but
133 is limited to returning at most PATH_MAX bytes. (Before Linux 3.12,
134 the limit on the size of the returned pathname was the system page
135 size. On many architectures, PATH_MAX and the system page size are
136 both 4096 bytes, but a few architectures have a larger page size.) If
137 the length of the pathname of the current working directory exceeds
138 this limit, then the system call fails with the error ENAMETOOLONG. In
139 this case, the library functions fall back to a (slower) alternative
140 implementation that returns the full pathname.
141 Following a change in Linux 2.6.36, the pathname returned by the
143 getcwd() system call will be prefixed with the string "(unreachable)"
144 if the current directory is not below the root directory of the current
145 process (e.g., because the process set a new filesystem root using
146 chroot(2) without changing its current directory into the new root).
147 Such behavior can also be caused by an unprivileged user by changing
148 the current directory into another mount namespace. When dealing with
149 pathname from untrusted sources, callers of the functions described in
150 this page should consider checking whether the returned pathname starts
151 with '/' or '(' to avoid misinterpreting an unreachable path as a rela‐
152 tive pathname.
153
155 Since the Linux 2.6.36 change that added "(unreachable)" in the circum‐
156 stances described above, the glibc implementation of getcwd() has
157 failed to conform to POSIX and returned a relative pathname when the
158 API contract requires an absolute pathname. With glibc 2.27 onwards
159 this is corrected; calling getcwd() from such a pathname will now
160 result in failure with ENOENT.
161
163 pwd(1), chdir(2), fchdir(2), open(2), unlink(2), free(3), malloc(3)
164
166 This page is part of release 5.04 of the Linux man-pages project. A
167 description of the project, information about reporting bugs, and the
168 latest version of this page, can be found at
169 https://www.kernel.org/doc/man-pages/.
170GNU 2018-04-30 GETCWD(3)