1CHOWN(P) POSIX Programmer's Manual CHOWN(P)
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6 chown - change owner and group of a file
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9 #include <unistd.h>
10 int chown(const char *path, uid_t owner, gid_t group);
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15 The chown() function shall change the user and group ownership of a
16 file.
17 The path argument points to a pathname naming a file. The user ID and
19 group ID of the named file shall be set to the numeric values contained
20 in owner and group, respectively.
21 Only processes with an effective user ID equal to the user ID of the
23 file or with appropriate privileges may change the ownership of a file.
24 If _POSIX_CHOWN_RESTRICTED is in effect for path:
25 * Changing the user ID is restricted to processes with appropriate
27 privileges.
28 * Changing the group ID is permitted to a process with an effective
30 user ID equal to the user ID of the file, but without appropriate
31 privileges, if and only if owner is equal to the file's user ID or (
32 uid_t)-1 and group is equal either to the calling process' effective
33 group ID or to one of its supplementary group IDs.
34 If the specified file is a regular file, one or more of the S_IXUSR,
36 S_IXGRP, or S_IXOTH bits of the file mode are set, and the process does
37 not have appropriate privileges, the set-user-ID (S_ISUID) and set-
38 group-ID (S_ISGID) bits of the file mode shall be cleared upon success‐
39 ful return from chown(). If the specified file is a regular file, one
40 or more of the S_IXUSR, S_IXGRP, or S_IXOTH bits of the file mode are
41 set, and the process has appropriate privileges, it is implementation-
42 defined whether the set-user-ID and set-group-ID bits are altered. If
43 the chown() function is successfully invoked on a file that is not a
44 regular file and one or more of the S_IXUSR, S_IXGRP, or S_IXOTH bits
45 of the file mode are set, the set-user-ID and set-group-ID bits may be
46 cleared.
47 If owner or group is specified as ( uid_t)-1 or ( gid_t)-1, respec‐
49 tively, the corresponding ID of the file shall not be changed. If both
50 owner and group are -1, the times need not be updated.
51 Upon successful completion, chown() shall mark for update the st_ctime
53 field of the file.
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56 Upon successful completion, 0 shall be returned; otherwise, -1 shall be
57 returned and errno set to indicate the error. If -1 is returned, no
58 changes are made in the user ID and group ID of the file.
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61 The chown() function shall fail if:
62 EACCES Search permission is denied on a component of the path prefix.
64 ELOOP A loop exists in symbolic links encountered during resolution of
66 the path argument.
67 ENAMETOOLONG
69 The length of the path argument exceeds {PATH_MAX} or a pathname
70 component is longer than {NAME_MAX}.
71 ENOTDIR
73 A component of the path prefix is not a directory.
74 ENOENT A component of path does not name an existing file or path is an
76 empty string.
77 EPERM The effective user ID does not match the owner of the file, or
79 the calling process does not have appropriate privileges and
80 _POSIX_CHOWN_RESTRICTED indicates that such privilege is
81 required.
82 EROFS The named file resides on a read-only file system.
84 The chown() function may fail if:
87 EIO An I/O error occurred while reading or writing to the file sys‐
89 tem.
90 EINTR The chown() function was interrupted by a signal which was
92 caught.
93 EINVAL The owner or group ID supplied is not a value supported by the
95 implementation.
96 ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
98 resolution of the path argument.
99 ENAMETOOLONG
101 As a result of encountering a symbolic link in resolution of the
102 path argument, the length of the substituted pathname string
103 exceeded {PATH_MAX}.
104 The following sections are informative.
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109 None.
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112 Although chown() can be used on some implementations by the file owner
113 to change the owner and group to any desired values, the only portable
114 use of this function is to change the group of a file to the effective
115 GID of the calling process or to a member of its group set.
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118 System III and System V allow a user to give away files; that is, the
119 owner of a file may change its user ID to anything. This is a serious
120 problem for implementations that are intended to meet government secu‐
121 rity regulations. Version 7 and 4.3 BSD permit only the superuser to
122 change the user ID of a file. Some government agencies (usually not
123 ones concerned directly with security) find this limitation too confin‐
124 ing. This volume of IEEE Std 1003.1-2001 uses may to permit secure
125 implementations while not disallowing System V.
126 System III and System V allow the owner of a file to change the group
128 ID to anything. Version 7 permits only the superuser to change the
129 group ID of a file. 4.3 BSD permits the owner to change the group ID of
130 a file to its effective group ID or to any of the groups in the list of
131 supplementary group IDs, but to no others.
132 The POSIX.1-1990 standard requires that the chown() function invoked by
134 a non-appropriate privileged process clear the S_ISGID and the S_ISUID
135 bits for regular files, and permits them to be cleared for other types
136 of files. This is so that changes in accessibility do not accidentally
137 cause files to become security holes. Unfortunately, requiring these
138 bits to be cleared on non-executable data files also clears the manda‐
139 tory file locking bit (shared with S_ISGID), which is an extension on
140 many implementations (it first appeared in System V). These bits should
141 only be required to be cleared on regular files that have one or more
142 of their execute bits set.
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145 None.
146
148 chmod() , pathconf() , the Base Definitions volume of
149 IEEE Std 1003.1-2001, <sys/types.h>, <unistd.h>
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152 Portions of this text are reprinted and reproduced in electronic form
153 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
154 -- Portable Operating System Interface (POSIX), The Open Group Base
155 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
156 Electrical and Electronics Engineers, Inc and The Open Group. In the
157 event of any discrepancy between this version and the original IEEE and
158 The Open Group Standard, the original IEEE and The Open Group Standard
159 is the referee document. The original Standard can be obtained online
160 at http://www.opengroup.org/unix/online.html .
161IEEE/The Open Group 2003 CHOWN(P)