man2/chmod.2

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   3 .\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
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  25 .\" Modified by Michael Haardt <michael@moria.de>
  26 .\" Modified 1993-07-21 by Rik Faith <faith@cs.unc.edu>
  27 .\" Modified 1997-01-12 by Michael Haardt
  28 .\"   <michael@cantor.informatik.rwth-aachen.de>: NFS details
  29 .\" Modified 2004-06-23 by Michael Kerrisk <mtk-manpages@gmx.net>
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  31 .TH CHMOD 2 2007-07-26 "Linux" "Linux Programmer's Manual"
  32 .SH NAME
  33 chmod, fchmod \- change permissions of a file
  34 .SH SYNOPSIS
  35 .B #include <sys/stat.h>
  36 .sp
  37 .BI "int chmod(const char *" path ", mode_t " mode );
  38 .br
  39 .BI "int fchmod(int " fildes ", mode_t " mode );
  40 .sp
  41 .in -4n
  42 Feature Test Macro Requirements for glibc (see
  43 .BR feature_test_macros (7)):
  44 .in
  45 .sp
  46 .BR fchmod ():
  47 _BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
  48 .SH DESCRIPTION
  49 The mode of the file given by
  50 .I path
  51 or referenced by
  52 .I fildes
  53 is changed.
  54
  55 Modes are specified by
  56 .IR or'ing
  57 the following:
  58 .RS
  59 .TP 1.0i
  60 .B S_ISUID
  61 04000 set user ID on execution
  62 .TP
  63 .B S_ISGID
  64 02000 set group ID on execution
  65 .TP
  66 .B S_ISVTX
  67 01000 sticky bit
  68 .TP
  69 .B S_IRUSR
  70 00400 read by owner
  71 .TP
  72 .B S_IWUSR
  73 00200 write by owner
  74 .TP
  75 .B S_IXUSR
  76 00100 execute/search by owner
  77 .TP
  78 .B S_IRGRP
  79 00040 read by group
  80 .TP
  81 .B S_IWGRP
  82 00020 write by group
  83 .TP
  84 .B S_IXGRP
  85 00010 execute/search by group
  86 .TP
  87 .B S_IROTH
  88 00004 read by others
  89 .TP
  90 .B S_IWOTH
  91 00002 write by others
  92 .TP
  93 .B S_IXOTH
  94 00001 execute/search by others
  95 .RE
  96 .PP
  97 The effective UID of the calling process must match the owner of the file,
  98 or the process must be privileged (Linux: it must have the
  99 .B CAP_FOWNER
 100 capability).
 101
 102 If the calling process is not privileged (Linux: does not have the
 103 .B CAP_FSETID
 104 capability), and the group of the file does not match
 105 the effective group ID of the process or one of its
 106 supplementary group IDs, the
 107 .B S_ISGID
 108 bit will be turned off,
 109 but this will not cause an error to be returned.
 110
 111 As a security measure, depending on the file system,
 112 the set-user-ID and set-group-ID execution bits
 113 may be turned off if a file is written.
 114 (On Linux this occurs if the writing process does not have the
 115 .B CAP_FSETID
 116 capability.)
 117 On some file systems, only the superuser can set the sticky bit,
 118 which may have a special meaning.
 119 For the sticky bit, and for set-user-ID and set-group-ID bits on
 120 directories, see
 121 .BR stat (2).
 122
 123 On NFS file systems, restricting the permissions will immediately influence
 124 already open files, because the access control is done on the server, but
 125 open files are maintained by the client.
 126 Widening the permissions may be
 127 delayed for other clients if attribute caching is enabled on them.
 128 .SH "RETURN VALUE"
 129 On success, zero is returned.
 130 On error, \-1 is returned, and
 131 .I errno
 132 is set appropriately.
 133 .SH ERRORS
 134 Depending on the file system, other errors can be returned.
 135 The more general errors for
 136 .BR chmod ()
 137 are listed below:
 138 .TP
 139 .B EACCES
 140 Search permission is denied on a component of the path prefix.
 141 (See also
 142 .BR path_resolution (7).)
 143 .TP
 144 .B EFAULT
 145 .I path
 146 points outside your accessible address space.
 147 .TP
 148 .B EIO
 149 An I/O error occurred.
 150 .TP
 151 .B ELOOP
 152 Too many symbolic links were encountered in resolving
 153 .IR path .
 154 .TP
 155 .B ENAMETOOLONG
 156 .I path
 157 is too long.
 158 .TP
 159 .B ENOENT
 160 The file does not exist.
 161 .TP
 162 .B ENOMEM
 163 Insufficient kernel memory was available.
 164 .TP
 165 .B ENOTDIR
 166 A component of the path prefix is not a directory.
 167 .TP
 168 .B EPERM
 169 The effective UID does not match the owner of the file,
 170 and the process is not privileged (Linux: it does not have the
 171 .B CAP_FOWNER
 172 capability).
 173 .TP
 174 .B EROFS
 175 The named file resides on a read-only file system.
 176 .PP
 177 The general errors for
 178 .BR fchmod ()
 179 are listed below:
 180 .TP
 181 .B EBADF
 182 The file descriptor
 183 .I fildes
 184 is not valid.
 185 .TP
 186 .B EIO
 187 See above.
 188 .TP
 189 .B EPERM
 190 See above.
 191 .TP
 192 .B EROFS
 193 See above.
 194 .SH "CONFORMING TO"
 195 4.4BSD, SVr4, POSIX.1-2001.
 196 .SH "SEE ALSO"
 197 .BR chown (2),
 198 .BR execve (2),
 199 .BR fchmodat (2),
 200 .BR open (2),
 201 .BR stat (2),
 202 .BR path_resolution (7)