1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)chmod.2 8.1 (Berkeley) 6/4/93 29.\" $FreeBSD$ 30.\" 31.Dd March 30, 2021 32.Dt CHMOD 2 33.Os 34.Sh NAME 35.Nm chmod , 36.Nm fchmod , 37.Nm lchmod , 38.Nm fchmodat 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 fchmod "int fd" "mode_t mode" 48.Ft int 49.Fn lchmod "const char *path" "mode_t mode" 50.Ft int 51.Fn fchmodat "int fd" "const char *path" "mode_t mode" "int flag" 52.Sh DESCRIPTION 53The file permission bits of the file named specified by 54.Fa path 55or referenced by the file descriptor 56.Fa fd 57are changed to 58.Fa mode . 59The 60.Fn chmod 61system call verifies that the process owner (user) either owns 62the file specified by 63.Fa path 64(or 65.Fa fd ) , 66or 67is the super-user. 68The 69.Fn chmod 70system call follows symbolic links to operate on the target of the link 71rather than the link itself. 72.Pp 73The 74.Fn lchmod 75system call is similar to 76.Fn chmod 77but does not follow symbolic links. 78.Pp 79The 80.Fn fchmodat 81is equivalent to either 82.Fn chmod 83or 84.Fn lchmod 85depending on the 86.Fa flag 87except in the case where 88.Fa path 89specifies a relative path. 90In this case the file to be changed is determined relative to the directory 91associated with the file descriptor 92.Fa fd 93instead of the current working directory. 94The values for the 95.Fa flag 96are constructed by a bitwise-inclusive OR of flags from the following list, defined 97in 98.In fcntl.h : 99.Bl -tag -width indent 100.It Dv AT_SYMLINK_NOFOLLOW 101If 102.Fa path 103names a symbolic link, then the mode of the symbolic link is changed. 104.It Dv AT_RESOLVE_BENEATH 105Only walk paths below the directory specified by the 106.Ar fd 107descriptor. 108See the description of the 109.Dv O_RESOLVE_BENEATH 110flag in the 111.Xr open 2 112manual page. 113.It Dv AT_EMPTY_PATH 114If the 115.Fa path 116argument is an empty string, operate on the file or directory 117referenced by the descriptor 118.Fa fd . 119If 120.Fa fd 121is equal to 122.Dv AT_FDCWD , 123operate on the current working directory. 124.El 125.Pp 126If 127.Fn fchmodat 128is passed the special value 129.Dv AT_FDCWD 130in the 131.Fa fd 132parameter, the current working directory is used. 133If also 134.Fa flag 135is zero, the behavior is identical to a call to 136.Fn chmod . 137.Pp 138A mode is created from 139.Em or'd 140permission bit masks 141defined in 142.In sys/stat.h : 143.Pp 144.Bd -literal -offset indent -compact 145#define S_IRWXU 0000700 /* RWX mask for owner */ 146#define S_IRUSR 0000400 /* R for owner */ 147#define S_IWUSR 0000200 /* W for owner */ 148#define S_IXUSR 0000100 /* X for owner */ 149 150#define S_IRWXG 0000070 /* RWX mask for group */ 151#define S_IRGRP 0000040 /* R for group */ 152#define S_IWGRP 0000020 /* W for group */ 153#define S_IXGRP 0000010 /* X for group */ 154 155#define S_IRWXO 0000007 /* RWX mask for other */ 156#define S_IROTH 0000004 /* R for other */ 157#define S_IWOTH 0000002 /* W for other */ 158#define S_IXOTH 0000001 /* X for other */ 159 160#define S_ISUID 0004000 /* set user id on execution */ 161#define S_ISGID 0002000 /* set group id on execution */ 162#define S_ISVTX 0001000 /* sticky bit */ 163.Ed 164.Pp 165The non-standard 166.Dv S_ISTXT 167is a synonym for 168.Dv S_ISVTX . 169.Pp 170The 171.Fx 172VM system totally ignores the sticky bit 173.Pq Dv S_ISVTX 174for executables. 175On UFS-based file systems (FFS, LFS) the sticky 176bit may only be set upon directories. 177.Pp 178If mode 179.Dv S_ISVTX 180(the `sticky bit') is set on a directory, 181an unprivileged user may not delete or rename 182files of other users in that directory. 183The sticky bit may be 184set by any user on a directory which the user owns or has appropriate 185permissions. 186For more details of the properties of the sticky bit, see 187.Xr sticky 7 . 188.Pp 189If mode ISUID (set UID) is set on a directory, 190and the MNT_SUIDDIR option was used in the mount of the file system, 191then the owner of any new files and sub-directories 192created within this directory are set 193to be the same as the owner of that directory. 194If this function is enabled, new directories will inherit 195the bit from their parents. 196Execute bits are removed from 197the file, and it will not be given to root. 198This behavior does not change the 199requirements for the user to be allowed to write the file, but only the eventual 200owner after it has been created. 201Group inheritance is not affected. 202.Pp 203This feature is designed for use on fileservers serving PC users via 204ftp, SAMBA, or netatalk. 205It provides security holes for shell users and as 206such should not be used on shell machines, especially on home directories. 207This option requires the SUIDDIR 208option in the kernel to work. 209Only UFS file systems support this option. 210For more details of the suiddir mount option, see 211.Xr mount 8 . 212.Pp 213Writing or changing the owner of a file 214turns off the set-user-id and set-group-id bits 215unless the user is the super-user. 216This makes the system somewhat more secure 217by protecting set-user-id (set-group-id) files 218from remaining set-user-id (set-group-id) if they are modified, 219at the expense of a degree of compatibility. 220.Sh RETURN VALUES 221.Rv -std 222.Sh ERRORS 223The 224.Fn chmod 225system call 226will fail and the file mode will be unchanged if: 227.Bl -tag -width Er 228.It Bq Er ENOTDIR 229A component of the path prefix is not a directory. 230.It Bq Er ENAMETOOLONG 231A component of a pathname exceeded 255 characters, 232or an entire path name exceeded 1023 characters. 233.It Bq Er ENOENT 234The named file does not exist. 235.It Bq Er EACCES 236Search permission is denied for a component of the path prefix. 237.It Bq Er ELOOP 238Too many symbolic links were encountered in translating the pathname. 239.It Bq Er EPERM 240The effective user ID does not match the owner of the file and 241the effective user ID is not the super-user. 242.It Bq Er EPERM 243The effective user ID is not the super-user, the effective user ID do match the 244owner of the file, but the group ID of the file does not match the effective 245group ID nor one of the supplementary group IDs. 246.It Bq Er EPERM 247The named file has its immutable or append-only flag set, see the 248.Xr chflags 2 249manual page for more information. 250.It Bq Er EROFS 251The named file resides on a read-only file system. 252.It Bq Er EFAULT 253The 254.Fa path 255argument 256points outside the process's allocated address space. 257.It Bq Er EIO 258An I/O error occurred while reading from or writing to the file system. 259.It Bq Er EINTEGRITY 260Corrupted data was detected while reading from the file system. 261.It Bq Er EFTYPE 262The effective user ID is not the super-user, the mode includes the sticky bit 263.Dv ( S_ISVTX ) , 264and path does not refer to a directory. 265.El 266.Pp 267The 268.Fn fchmod 269system call will fail if: 270.Bl -tag -width Er 271.It Bq Er EBADF 272The descriptor is not valid. 273.It Bq Er EINVAL 274The 275.Fa fd 276argument 277refers to a socket, not to a file. 278.It Bq Er EROFS 279The file resides on a read-only file system. 280.It Bq Er EIO 281An I/O error occurred while reading from or writing to the file system. 282.It Bq Er EINTEGRITY 283Corrupted data was detected while reading from the file system. 284.El 285.Pp 286In addition to the 287.Fn chmod 288errors, 289.Fn fchmodat 290fails if: 291.Bl -tag -width Er 292.It Bq Er EBADF 293The 294.Fa path 295argument does not specify an absolute path and the 296.Fa fd 297argument is neither 298.Fa AT_FDCWD 299nor a valid file descriptor open for searching. 300.It Bq Er EINVAL 301The value of the 302.Fa flag 303argument is not valid. 304.It Bq Er ENOTDIR 305The 306.Fa path 307argument is not an absolute path and 308.Fa fd 309is neither 310.Dv AT_FDCWD 311nor a file descriptor associated with a directory. 312.It Bq Er ENOTCAPABLE 313.Fa path 314is an absolute path, 315or contained a ".." component leading to a 316directory outside of the directory hierarchy specified by 317.Fa fd , 318and the process is in capability mode or the 319.Dv AT_RESOLVE_BENEATH 320flag was specified. 321.El 322.Sh SEE ALSO 323.Xr chmod 1 , 324.Xr chflags 2 , 325.Xr chown 2 , 326.Xr open 2 , 327.Xr stat 2 , 328.Xr sticky 7 329.Sh STANDARDS 330The 331.Fn chmod 332system call is expected to conform to 333.St -p1003.1-90 , 334except for the return of 335.Er EFTYPE . 336The 337.Dv S_ISVTX 338bit on directories is expected to conform to 339.St -susv3 . 340The 341.Fn fchmodat 342system call is expected to conform to 343.St -p1003.1-2008 . 344.Sh HISTORY 345The 346.Fn chmod 347function appeared in 348.At v1 . 349The 350.Fn fchmod 351system call appeared in 352.Bx 4.2 . 353The 354.Fn lchmod 355system call appeared in 356.Fx 3.0 . 357The 358.Fn fchmodat 359system call appeared in 360.Fx 8.0 . 361