| .\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de) |
| .\" |
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| .\" Since the Linux kernel and libraries are constantly changing, this |
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| .\" Modified Wed Jul 21 22:35:42 1993 by Rik Faith (faith@cs.unc.edu) |
| .\" Modified 18 Mar 1996 by Martin Schulze (joey@infodrom.north.de): |
| .\" Corrected description of getwd(). |
| .\" Modified Sat Aug 21 12:32:12 MET 1999 by aeb - applied fix by aj |
| .\" 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 2021-03-22 "GNU" "Linux Programmer's Manual" |
| .SH NAME |
| getcwd, getwd, get_current_dir_name \- get current working directory |
| .SH SYNOPSIS |
| .nf |
| .B #include <unistd.h> |
| .PP |
| .BI "char *getcwd(char *" buf ", size_t " size ); |
| .BI "char *getwd(char *" buf ); |
| .B "char *get_current_dir_name(void);" |
| .fi |
| .PP |
| .RS -4 |
| Feature Test Macro Requirements for glibc (see |
| .BR feature_test_macros (7)): |
| .RE |
| .PP |
| .BR get_current_dir_name (): |
| .nf |
| _GNU_SOURCE |
| .fi |
| .PP |
| .BR getwd (): |
| .nf |
| Since glibc 2.12: |
| (_XOPEN_SOURCE >= 500) && ! (_POSIX_C_SOURCE >= 200809L) |
| || /* Glibc since 2.19: */ _DEFAULT_SOURCE |
| || /* Glibc <= 2.19: */ _BSD_SOURCE |
| Before glibc 2.12: |
| _BSD_SOURCE || _XOPEN_SOURCE >= 500 |
| .\" || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED |
| .fi |
| .SH DESCRIPTION |
| 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 |
| .IR buf , |
| if present. |
| .PP |
| The |
| .BR getcwd () |
| function copies an absolute pathname of the current working directory |
| to the array pointed to by |
| .IR buf , |
| which is of length |
| .IR size . |
| .PP |
| If the length of the absolute pathname of the current working directory, |
| including the terminating null byte, exceeds |
| .I size |
| bytes, NULL is returned, and |
| .I errno |
| is set to |
| .BR ERANGE ; |
| an application should check for this error, and allocate a larger |
| buffer if necessary. |
| .PP |
| As an extension to the POSIX.1-2001 standard, glibc's |
| .BR getcwd () |
| allocates the buffer dynamically using |
| .BR malloc (3) |
| if |
| .I buf |
| is NULL. |
| In this case, the allocated buffer has the length |
| .I size |
| unless |
| .I size |
| is zero, when |
| .I buf |
| is allocated as big as necessary. |
| The caller should |
| .BR free (3) |
| the returned buffer. |
| .PP |
| .BR get_current_dir_name () |
| will |
| .BR malloc (3) |
| an array big enough to hold the absolute pathname of |
| the current working directory. |
| If the environment |
| variable |
| .B PWD |
| is set, and its value is correct, then that value will be returned. |
| The caller should |
| .BR free (3) |
| the returned buffer. |
| .PP |
| .BR getwd () |
| does not |
| .BR malloc (3) |
| any memory. |
| The |
| .I buf |
| argument should be a pointer to an array at least |
| .B PATH_MAX |
| bytes long. |
| If the length of the absolute pathname of the current working directory, |
| including the terminating null byte, exceeds |
| .B PATH_MAX |
| bytes, NULL is returned, and |
| .I errno |
| is set to |
| .BR ENAMETOOLONG . |
| (Note that on some systems, |
| .B PATH_MAX |
| may not be a compile-time constant; |
| furthermore, its value may depend on the filesystem, see |
| .BR pathconf (3).) |
| For portability and security reasons, use of |
| .BR getwd () |
| is deprecated. |
| .SH RETURN VALUE |
| On success, these functions return a pointer to a string containing |
| the pathname of the current working directory. |
| In the case of |
| .BR getcwd () |
| and |
| .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. |
| The contents of the array pointed to by |
| .I buf |
| are undefined on error. |
| .SH ERRORS |
| .TP |
| .B EACCES |
| Permission to read or search a component of the filename was denied. |
| .TP |
| .B EFAULT |
| .I buf |
| points to a bad address. |
| .TP |
| .B EINVAL |
| The |
| .I size |
| argument is zero and |
| .I buf |
| is not a null pointer. |
| .TP |
| .B EINVAL |
| .BR getwd (): |
| .I buf |
| is NULL. |
| .TP |
| .B ENAMETOOLONG |
| .BR getwd (): |
| The size of the null-terminated absolute pathname string exceeds |
| .B PATH_MAX |
| bytes. |
| .TP |
| .B ENOENT |
| The current working directory has been unlinked. |
| .TP |
| .B ENOMEM |
| Out of memory. |
| .TP |
| .B ERANGE |
| The |
| .I size |
| argument is less than the length of the absolute pathname of the |
| working directory, including the terminating null byte. |
| You need to allocate a bigger array and try again. |
| .SH ATTRIBUTES |
| For an explanation of the terms used in this section, see |
| .BR attributes (7). |
| .ad l |
| .nh |
| .TS |
| allbox; |
| lbx lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR getcwd (), |
| .BR getwd () |
| T} Thread safety MT-Safe |
| T{ |
| .BR get_current_dir_name () |
| T} Thread safety MT-Safe env |
| .TE |
| .hy |
| .ad |
| .sp 1 |
| .SH CONFORMING TO |
| .BR getcwd () |
| conforms to POSIX.1-2001. |
| Note however that POSIX.1-2001 leaves the behavior of |
| .BR getcwd () |
| 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 |
| .BR getwd (). |
| Use |
| .BR getcwd () |
| instead. |
| 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, these functions make use of the |
| .BR getcwd () |
| 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 . |
| .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 |
| directory (".") and calling |
| .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), |
| .BR fchdir (2), |
| .BR open (2), |
| .BR unlink (2), |
| .BR free (3), |
| .BR malloc (3) |