| GETCWD(3) | Linux Programmer's Manual | GETCWD(3) |
getcwd, getwd, get_current_dir_name - get current working directory
#include <unistd.h>
char *getcwd(char *buf, size_t size);
char *getwd(char *buf);
char *get_current_dir_name(void);
get_current_dir_name():
getwd():
(_XOPEN_SOURCE >= 500) && ! (_POSIX_C_SOURCE >= 200809L)
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE
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 buf, if present.
The getcwd() function copies an absolute pathname of the current working directory to the array pointed to by buf, which is of length size.
If the length of the absolute pathname of the current working directory, including the terminating null byte, exceeds size bytes, NULL is returned, and errno is set to ERANGE; an application should check for this error, and allocate a larger buffer if necessary.
As an extension to the POSIX.1-2001 standard, glibc's getcwd() allocates the buffer dynamically using malloc(3) if buf is NULL. In this case, the allocated buffer has the length size unless size is zero, when buf is allocated as big as necessary. The caller should free(3) the returned buffer.
get_current_dir_name() will malloc(3) an array big enough to hold the absolute pathname of the current working directory. If the environment variable PWD is set, and its value is correct, then that value will be returned. The caller should free(3) the returned buffer.
getwd() does not malloc(3) any memory. The buf argument should be a pointer to an array at least PATH_MAX bytes long. If the length of the absolute pathname of the current working directory, including the terminating null byte, exceeds PATH_MAX bytes, NULL is returned, and errno is set to ENAMETOOLONG. (Note that on some systems, PATH_MAX may not be a compile-time constant; furthermore, its value may depend on the filesystem, see pathconf(3).) For portability and security reasons, use of getwd() is deprecated.
On success, these functions return a pointer to a string containing the pathname of the current working directory. In the case of getcwd() and getwd() this is the same value as buf.
On failure, these functions return NULL, and errno is set to indicate the error. The contents of the array pointed to by buf are undefined on error.
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
| getcwd (), getwd () | Thread safety | MT-Safe |
| get_current_dir_name () | Thread safety | MT-Safe env |
getcwd() conforms to POSIX.1-2001. Note however that POSIX.1-2001 leaves the behavior of getcwd() unspecified if buf is NULL.
getwd() is present in POSIX.1-2001, but marked LEGACY. POSIX.1-2008 removes the specification of getwd(). Use getcwd() instead. POSIX.1-2001 does not define any errors for getwd().
get_current_dir_name() is a GNU extension.
Under Linux, these functions make use of the getcwd() system call (available since Linux 2.1.92). On older systems they would query /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 EACCES.
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 directory (".") and calling 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.
On Linux, the kernel provides a 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 PATH_MAX bytes. (Before Linux 3.12, the limit on the size of the returned pathname was the system page size. On many architectures, 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 ENAMETOOLONG. In this case, the library functions fall back to a (slower) alternative implementation that returns the full pathname.
Following a change in Linux 2.6.36, the pathname returned by the 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 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.
Since the Linux 2.6.36 change that added "(unreachable)" in the circumstances described above, the glibc implementation of 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 getcwd() from such a pathname will now result in failure with ENOENT.
pwd(1), chdir(2), fchdir(2), open(2), unlink(2), free(3), malloc(3)
This page is part of release 5.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
| 2018-04-30 | GNU |