1.\" $NetBSD: chmod.2,v 1.37 2010/05/31 12:16:20 njoly Exp $ 2.\" 3.\" Copyright (c) 1980, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)chmod.2 8.1 (Berkeley) 6/4/93 31.\" 32.Dd January 4, 2009 33.Dt CHMOD 2 34.Os 35.Sh NAME 36.Nm chmod , 37.Nm lchmod , 38.Nm fchmod 39.Nd change mode of file 40.Sh LIBRARY 41.Lb libc 42.Sh SYNOPSIS 43.In sys/stat.h 44.Ft int 45.Fn chmod "const char *path" "mode_t mode" 46.Ft int 47.Fn lchmod "const char *path" "mode_t mode" 48.Ft int 49.Fn fchmod "int fd" "mode_t mode" 50.Sh DESCRIPTION 51The function 52.Fn chmod 53sets the file permission bits 54of the file 55specified by the pathname 56.Fa path 57to 58.Fa mode . 59.Fn fchmod 60sets the permission bits of the specified 61file descriptor 62.Fa fd . 63.Fn lchmod 64is like 65.Fn chmod 66except in the case where the named file is a symbolic link, 67in which case 68.Fn lchmod 69sets the permission bits of the link, 70while 71.Fn chmod 72sets the bits of the file the link references. 73.Fn chmod 74verifies that the process owner (user) either owns 75the file specified by 76.Fa path 77(or 78.Fa fd ) , 79or 80is the super-user. 81A mode is created from 82.Em or'd 83permission bit masks 84defined in 85.In sys/stat.h : 86.Bd -literal -offset indent -compact 87#define S_IRWXU 0000700 /* RWX mask for owner */ 88#define S_IRUSR 0000400 /* R for owner */ 89#define S_IWUSR 0000200 /* W for owner */ 90#define S_IXUSR 0000100 /* X for owner */ 91 92#define S_IRWXG 0000070 /* RWX mask for group */ 93#define S_IRGRP 0000040 /* R for group */ 94#define S_IWGRP 0000020 /* W for group */ 95#define S_IXGRP 0000010 /* X for group */ 96 97#define S_IRWXO 0000007 /* RWX mask for other */ 98#define S_IROTH 0000004 /* R for other */ 99#define S_IWOTH 0000002 /* W for other */ 100#define S_IXOTH 0000001 /* X for other */ 101 102#define S_ISUID 0004000 /* set user id on execution */ 103#define S_ISGID 0002000 /* set group id on execution */ 104#define S_ISVTX 0001000 /* save swapped text even after use */ 105.Ed 106.Pp 107If mode 108.Dv ISVTX 109(the 110.Sq sticky bit ) 111is set on a regular file, it historically meant that the system should 112save a shareable copy of the program text in the swap area. 113When applied to commonly used programs like the shell or editor, this 114would decrease memory usage and startup time. 115In 116.Nx , 117the sticky bit may still be set on regular files by the super-user, 118but has no effect. 119The historical meaning became obsolete in the 1980s with the advent of 120memory-mapped executables, and is only documented as a matter of 121historical interest. 122.Pp 123If mode 124.Dv ISVTX 125(the 126.Sq sticky bit ) 127is set on a directory, 128an unprivileged user may not delete or rename 129files of other users in that directory. 130The sticky bit may be set by any user on a directory which the user 131owns or has appropriate permissions. 132.Pp 133For more information about the properties of the sticky bit, see 134.Xr sticky 7 . 135.Pp 136Changing the owner of a file 137turns off the set-user-id and set-group-id bits; 138writing to a file 139turns off the set-user-id and set-group-id bits 140unless the user is the super-user. 141This makes the system somewhat more secure 142by protecting set-user-id (set-group-id) files 143from remaining set-user-id (set-group-id) if they are modified, 144at the expense of a degree of compatibility. 145.Sh RETURN VALUES 146Upon successful completion, a value of 0 is returned. 147Otherwise, a value of \-1 is returned and 148.Va errno 149is set to indicate the error. 150.Sh ERRORS 151.Fn chmod 152and 153.Fn lchmod 154will fail and the file mode will be unchanged if: 155.Bl -tag -width Er 156.It Bq Er ENOTDIR 157A component of the path prefix is not a directory. 158.It Bq Er ENAMETOOLONG 159A component of a pathname exceeded 160.Brq Dv NAME_MAX 161characters, or an entire path name exceeded 162.Brq Dv PATH_MAX 163characters. 164.It Bq Er ENOENT 165The named file does not exist. 166.It Bq Er EACCES 167Search permission is denied for a component of the path prefix. 168.It Bq Er ELOOP 169Too many symbolic links were encountered in translating the pathname. 170.It Bq Er EPERM 171The effective user ID does not match the owner of the file and 172the effective user ID is not the super-user. 173.It Bq Er EPERM 174The mode includes the setgid bit 175.Pq Dv S_ISGID 176but the file's group is neither the effective group ID nor is it in the 177group access list. 178.It Bq Er EROFS 179The named file resides on a read-only file system. 180.It Bq Er EFAULT 181.Fa path 182points outside the process's allocated address space. 183.It Bq Er EIO 184An I/O error occurred while reading from or writing to the file system. 185.It Bq Er EFTYPE 186The effective user ID is not the super-user, the 187.Fa mode 188includes the sticky bit 189.Pq Dv S_ISVTX , 190and 191.Fa path 192does not refer to a directory. 193.El 194.Pp 195.Fn fchmod 196will fail if: 197.Bl -tag -width Er 198.It Bq Er EBADF 199The descriptor is not valid. 200.It Bq Er EINVAL 201.Fa fd 202refers to a socket, not to a file. 203.It Bq Er EPERM 204The effective user ID does not match the owner of the file and 205the effective user ID is not the super-user. 206.It Bq Er EPERM 207The mode includes the setgid bit 208.Pq Dv S_ISGID 209but the file's group is neither the effective group ID nor is it in the 210group access list. 211.It Bq Er EROFS 212The file resides on a read-only file system. 213.It Bq Er EIO 214An I/O error occurred while reading from or writing to the file system. 215.It Bq Er EFTYPE 216The effective user ID is not the super-user, the 217.Fa mode 218includes the sticky bit 219.Pq Dv S_ISVTX , 220and 221.Fa fd 222does not refer to a directory. 223.El 224.Sh SEE ALSO 225.Xr chmod 1 , 226.Xr chflags 2 , 227.Xr chown 2 , 228.Xr open 2 , 229.Xr stat 2 , 230.Xr getmode 3 , 231.Xr setmode 3 , 232.Xr sticky 7 , 233.Xr symlink 7 234.Sh STANDARDS 235The 236.Fn chmod 237function conforms to 238.St -p1003.1-90 . 239.Sh HISTORY 240The 241.Fn fchmod 242function call 243appeared in 244.Bx 4.2 . 245The 246.Fn lchmod 247function call appeared in 248.Nx 1.3 . 249