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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 February 23, 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.El 114.Pp 115If 116.Fn fchmodat 117is passed the special value 118.Dv AT_FDCWD 119in the 120.Fa fd 121parameter, the current working directory is used. 122If also 123.Fa flag 124is zero, the behavior is identical to a call to 125.Fn chmod . 126.Pp 127A mode is created from 128.Em or'd 129permission bit masks 130defined in 131.In sys/stat.h : 132.Pp 133.Bd -literal -offset indent -compact 134#define S_IRWXU 0000700 /* RWX mask for owner */ 135#define S_IRUSR 0000400 /* R for owner */ 136#define S_IWUSR 0000200 /* W for owner */ 137#define S_IXUSR 0000100 /* X for owner */ 138 139#define S_IRWXG 0000070 /* RWX mask for group */ 140#define S_IRGRP 0000040 /* R for group */ 141#define S_IWGRP 0000020 /* W for group */ 142#define S_IXGRP 0000010 /* X for group */ 143 144#define S_IRWXO 0000007 /* RWX mask for other */ 145#define S_IROTH 0000004 /* R for other */ 146#define S_IWOTH 0000002 /* W for other */ 147#define S_IXOTH 0000001 /* X for other */ 148 149#define S_ISUID 0004000 /* set user id on execution */ 150#define S_ISGID 0002000 /* set group id on execution */ 151#define S_ISVTX 0001000 /* sticky bit */ 152.Ed 153.Pp 154The non-standard 155.Dv S_ISTXT 156is a synonym for 157.Dv S_ISVTX . 158.Pp 159The 160.Fx 161VM system totally ignores the sticky bit 162.Pq Dv S_ISVTX 163for executables. 164On UFS-based file systems (FFS, LFS) the sticky 165bit may only be set upon directories. 166.Pp 167If mode 168.Dv S_ISVTX 169(the `sticky bit') is set on a directory, 170an unprivileged user may not delete or rename 171files of other users in that directory. 172The sticky bit may be 173set by any user on a directory which the user owns or has appropriate 174permissions. 175For more details of the properties of the sticky bit, see 176.Xr sticky 7 . 177.Pp 178If mode ISUID (set UID) is set on a directory, 179and the MNT_SUIDDIR option was used in the mount of the file system, 180then the owner of any new files and sub-directories 181created within this directory are set 182to be the same as the owner of that directory. 183If this function is enabled, new directories will inherit 184the bit from their parents. 185Execute bits are removed from 186the file, and it will not be given to root. 187This behavior does not change the 188requirements for the user to be allowed to write the file, but only the eventual 189owner after it has been created. 190Group inheritance is not affected. 191.Pp 192This feature is designed for use on fileservers serving PC users via 193ftp, SAMBA, or netatalk. 194It provides security holes for shell users and as 195such should not be used on shell machines, especially on home directories. 196This option requires the SUIDDIR 197option in the kernel to work. 198Only UFS file systems support this option. 199For more details of the suiddir mount option, see 200.Xr mount 8 . 201.Pp 202Writing or changing the owner of a file 203turns off the set-user-id and set-group-id bits 204unless the user is the super-user. 205This makes the system somewhat more secure 206by protecting set-user-id (set-group-id) files 207from remaining set-user-id (set-group-id) if they are modified, 208at the expense of a degree of compatibility. 209.Sh RETURN VALUES 210.Rv -std 211.Sh ERRORS 212The 213.Fn chmod 214system call 215will fail and the file mode will be unchanged if: 216.Bl -tag -width Er 217.It Bq Er ENOTDIR 218A component of the path prefix is not a directory. 219.It Bq Er ENAMETOOLONG 220A component of a pathname exceeded 255 characters, 221or an entire path name exceeded 1023 characters. 222.It Bq Er ENOENT 223The named file does not exist. 224.It Bq Er EACCES 225Search permission is denied for a component of the path prefix. 226.It Bq Er ELOOP 227Too many symbolic links were encountered in translating the pathname. 228.It Bq Er EPERM 229The effective user ID does not match the owner of the file and 230the effective user ID is not the super-user. 231.It Bq Er EPERM 232The effective user ID is not the super-user, the effective user ID do match the 233owner of the file, but the group ID of the file does not match the effective 234group ID nor one of the supplementary group IDs. 235.It Bq Er EPERM 236The named file has its immutable or append-only flag set, see the 237.Xr chflags 2 238manual page for more information. 239.It Bq Er EROFS 240The named file resides on a read-only file system. 241.It Bq Er EFAULT 242The 243.Fa path 244argument 245points outside the process's allocated address space. 246.It Bq Er EIO 247An I/O error occurred while reading from or writing to the file system. 248.It Bq Er EINTEGRITY 249Corrupted data was detected while reading from the file system. 250.It Bq Er EFTYPE 251The effective user ID is not the super-user, the mode includes the sticky bit 252.Dv ( S_ISVTX ) , 253and path does not refer to a directory. 254.El 255.Pp 256The 257.Fn fchmod 258system call will fail if: 259.Bl -tag -width Er 260.It Bq Er EBADF 261The descriptor is not valid. 262.It Bq Er EINVAL 263The 264.Fa fd 265argument 266refers to a socket, not to a file. 267.It Bq Er EROFS 268The file resides on a read-only file system. 269.It Bq Er EIO 270An I/O error occurred while reading from or writing to the file system. 271.It Bq Er EINTEGRITY 272Corrupted data was detected while reading from the file system. 273.El 274.Pp 275In addition to the 276.Fn chmod 277errors, 278.Fn fchmodat 279fails if: 280.Bl -tag -width Er 281.It Bq Er EBADF 282The 283.Fa path 284argument does not specify an absolute path and the 285.Fa fd 286argument is neither 287.Fa AT_FDCWD 288nor a valid file descriptor open for searching. 289.It Bq Er EINVAL 290The value of the 291.Fa flag 292argument is not valid. 293.It Bq Er ENOTDIR 294The 295.Fa path 296argument is not an absolute path and 297.Fa fd 298is neither 299.Dv AT_FDCWD 300nor a file descriptor associated with a directory. 301.It Bq Er ENOTCAPABLE 302.Fa path 303is an absolute path, 304or contained a ".." component leading to a 305directory outside of the directory hierarchy specified by 306.Fa fd , 307and the process is in capability mode or the 308.Dv AT_RESOLVE_BENEATH 309flag was specified. 310.El 311.Sh SEE ALSO 312.Xr chmod 1 , 313.Xr chflags 2 , 314.Xr chown 2 , 315.Xr open 2 , 316.Xr stat 2 , 317.Xr sticky 7 318.Sh STANDARDS 319The 320.Fn chmod 321system call is expected to conform to 322.St -p1003.1-90 , 323except for the return of 324.Er EFTYPE . 325The 326.Dv S_ISVTX 327bit on directories is expected to conform to 328.St -susv3 . 329The 330.Fn fchmodat 331system call is expected to conform to 332.St -p1003.1-2008 . 333.Sh HISTORY 334The 335.Fn chmod 336function appeared in 337.At v1 . 338The 339.Fn fchmod 340system call appeared in 341.Bx 4.2 . 342The 343.Fn lchmod 344system call appeared in 345.Fx 3.0 . 346The 347.Fn fchmodat 348system call appeared in 349.Fx 8.0 . 350