1CHOWN(3P) POSIX Programmer's Manual CHOWN(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
13 chown, fchownat — change owner and group of a file relative to direc‐
14 tory file descriptor
15
17 #include <unistd.h>
18 int chown(const char *path, uid_t owner, gid_t group);
20 int fchownat(int fd, const char *path, uid_t owner, gid_t group,
21 int flag);
22
24 The chown() function shall change the user and group ownership of a
25 file.
26 The path argument points to a pathname naming a file. The user ID and
28 group ID of the named file shall be set to the numeric values contained
29 in owner and group, respectively.
30 Only processes with an effective user ID equal to the user ID of the
32 file or with appropriate privileges may change the ownership of a file.
33 If _POSIX_CHOWN_RESTRICTED is in effect for path:
34 * Changing the user ID is restricted to processes with appropriate
36 privileges.
37 * Changing the group ID is permitted to a process with an effective
39 user ID equal to the user ID of the file, but without appropriate
40 privileges, if and only if owner is equal to the file's user ID or
41 (uid_t)−1 and group is equal either to the calling process' effec‐
42 tive group ID or to one of its supplementary group IDs.
43 If the specified file is a regular file, one or more of the S_IXUSR,
45 S_IXGRP, or S_IXOTH bits of the file mode are set, and the process does
46 not have appropriate privileges, the set-user-ID (S_ISUID) and set-
47 group-ID (S_ISGID) bits of the file mode shall be cleared upon success‐
48 ful return from chown(). If the specified file is a regular file, one
49 or more of the S_IXUSR, S_IXGRP, or S_IXOTH bits of the file mode are
50 set, and the process has appropriate privileges, it is implementation-
51 defined whether the set-user-ID and set-group-ID bits are altered. If
52 the chown() function is successfully invoked on a file that is not a
53 regular file and one or more of the S_IXUSR, S_IXGRP, or S_IXOTH bits
54 of the file mode are set, the set-user-ID and set-group-ID bits may be
55 cleared.
56 If owner or group is specified as (uid_t)−1 or (gid_t)−1, respectively,
58 the corresponding ID of the file shall not be changed. If both owner
59 and group are −1, the times need not be updated.
60 Upon successful completion, chown() shall mark for update the last file
62 status change timestamp of the file.
63 The fchownat() function shall be equivalent to the chown() and lchown()
65 functions except in the case where path specifies a relative path. In
66 this case the file to be changed is determined relative to the direc‐
67 tory associated with the file descriptor fd instead of the current
68 working directory. If the file descriptor was opened without O_SEARCH,
69 the function shall check whether directory searches are permitted using
70 the current permissions of the directory underlying the file descrip‐
71 tor. If the file descriptor was opened with O_SEARCH, the function
72 shall not perform the check.
73 Values for flag are constructed by a bitwise-inclusive OR of flags from
75 the following list, defined in <fcntl.h>:
76 AT_SYMLINK_NOFOLLOW
78 If path names a symbolic link, ownership of the symbolic link is
79 changed.
80 If fchownat() is passed the special value AT_FDCWD in the fd parameter,
82 the current working directory shall be used and the behavior shall be
83 identical to a call to chown() or lchown() respectively, depending on
84 whether or not the AT_SYMLINK_NOFOLLOW bit is set in the flag argument.
85
87 Upon successful completion, these functions shall return 0. Otherwise,
88 these functions shall return −1 and set errno to indicate the error. If
89 −1 is returned, no changes are made in the user ID and group ID of the
90 file.
91
93 These functions shall fail if:
94 EACCES Search permission is denied on a component of the path prefix.
96 ELOOP A loop exists in symbolic links encountered during resolution of
98 the path argument.
99 ENAMETOOLONG
101 The length of a component of a pathname is longer than
102 {NAME_MAX}.
103 ENOENT A component of path does not name an existing file or path is an
105 empty string.
106 ENOTDIR
108 A component of the path prefix names an existing file that is
109 neither a directory nor a symbolic link to a directory, or the
110 path argument contains at least one non-<slash> character and
111 ends with one or more trailing <slash> characters and the last
112 pathname component names an existing file that is neither a
113 directory nor a symbolic link to a directory.
114 EPERM The effective user ID does not match the owner of the file, or
116 the calling process does not have appropriate privileges and
117 _POSIX_CHOWN_RESTRICTED indicates that such privilege is
118 required.
119 EROFS The named file resides on a read-only file system.
121 The fchownat() function shall fail if:
123 EACCES fd was not opened with O_SEARCH and the permissions of the
125 directory underlying fd do not permit directory searches.
126 EBADF The path argument does not specify an absolute path and the fd
128 argument is neither AT_FDCWD nor a valid file descriptor open
129 for reading or searching.
130 ENOTDIR
132 The path argument is not an absolute path and fd is a file
133 descriptor associated with a non-directory file.
134 These functions may fail if:
136 EIO An I/O error occurred while reading or writing to the file sys‐
138 tem.
139 EINTR The chown() function was interrupted by a signal which was
141 caught.
142 EINVAL The owner or group ID supplied is not a value supported by the
144 implementation.
145 ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
147 resolution of the path argument.
148 ENAMETOOLONG
150 The length of a pathname exceeds {PATH_MAX}, or pathname resolu‐
151 tion of a symbolic link produced an intermediate result with a
152 length that exceeds {PATH_MAX}.
153 The fchownat() function may fail if:
155 EINVAL The value of the flag argument is not valid.
157 The following sections are informative.
159
161 None.
162
164 Although chown() can be used on some implementations by the file owner
165 to change the owner and group to any desired values, the only portable
166 use of this function is to change the group of a file to the effective
167 GID of the calling process or to a member of its group set.
168
170 System III and System V allow a user to give away files; that is, the
171 owner of a file may change its user ID to anything. This is a serious
172 problem for implementations that are intended to meet government secu‐
173 rity regulations. Version 7 and 4.3 BSD permit only the superuser to
174 change the user ID of a file. Some government agencies (usually not
175 ones concerned directly with security) find this limitation too confin‐
176 ing. This volume of POSIX.1‐2008 uses may to permit secure implementa‐
177 tions while not disallowing System V.
178 System III and System V allow the owner of a file to change the group
180 ID to anything. Version 7 permits only the superuser to change the
181 group ID of a file. 4.3 BSD permits the owner to change the group ID
182 of a file to its effective group ID or to any of the groups in the list
183 of supplementary group IDs, but to no others.
184 The POSIX.1‐1990 standard requires that the chown() function invoked by
186 a non-appropriate privileged process clear the S_ISGID and the S_ISUID
187 bits for regular files, and permits them to be cleared for other types
188 of files. This is so that changes in accessibility do not accidentally
189 cause files to become security holes. Unfortunately, requiring these
190 bits to be cleared on non-executable data files also clears the manda‐
191 tory file locking bit (shared with S_ISGID), which is an extension on
192 many implementations (it first appeared in System V). These bits should
193 only be required to be cleared on regular files that have one or more
194 of their execute bits set.
195 The purpose of the fchownat() function is to enable changing ownership
197 of files in directories other than the current working directory with‐
198 out exposure to race conditions. Any part of the path of a file could
199 be changed in parallel to a call to chown() or lchown(), resulting in
200 unspecified behavior. By opening a file descriptor for the target
201 directory and using the fchownat() function it can be guaranteed that
202 the changed file is located relative to the desired directory.
203
205 None.
206
208 chmod(), fpathconf(), lchown()
209 The Base Definitions volume of POSIX.1‐2008, <fcntl.h>, <sys_types.h>,
211 <unistd.h>
212
214 Portions of this text are reprinted and reproduced in electronic form
215 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
216 -- Portable Operating System Interface (POSIX), The Open Group Base
217 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
218 cal and Electronics Engineers, Inc and The Open Group. (This is
219 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
220 event of any discrepancy between this version and the original IEEE and
221 The Open Group Standard, the original IEEE and The Open Group Standard
222 is the referee document. The original Standard can be obtained online
223 at http://www.unix.org/online.html .
224 Any typographical or formatting errors that appear in this page are
226 most likely to have been introduced during the conversion of the source
227 files to man page format. To report such errors, see https://www.ker‐
228 nel.org/doc/man-pages/reporting_bugs.html .
229IEEE/The Open Group 2013 CHOWN(3P)