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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 September 23, 2020 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_BENEATH 105Only allow to change permissions of a file which is beneath of 106the topping directory. 107See the description of the 108.Dv O_BENEATH 109flag in the 110.Xr open 2 111manual page. 112.It Dv AT_RESOLVE_BENEATH 113Only walks paths below the topping directory. 114See the description of the 115.Dv O_RESOLVE_BENEATH 116flag in the 117.Xr open 2 118manual page. 119.El 120.Pp 121If 122.Fn fchmodat 123is passed the special value 124.Dv AT_FDCWD 125in the 126.Fa fd 127parameter, the current working directory is used. 128If also 129.Fa flag 130is zero, the behavior is identical to a call to 131.Fn chmod . 132.Pp 133A mode is created from 134.Em or'd 135permission bit masks 136defined in 137.In sys/stat.h : 138.Pp 139.Bd -literal -offset indent -compact 140#define S_IRWXU 0000700 /* RWX mask for owner */ 141#define S_IRUSR 0000400 /* R for owner */ 142#define S_IWUSR 0000200 /* W for owner */ 143#define S_IXUSR 0000100 /* X for owner */ 144 145#define S_IRWXG 0000070 /* RWX mask for group */ 146#define S_IRGRP 0000040 /* R for group */ 147#define S_IWGRP 0000020 /* W for group */ 148#define S_IXGRP 0000010 /* X for group */ 149 150#define S_IRWXO 0000007 /* RWX mask for other */ 151#define S_IROTH 0000004 /* R for other */ 152#define S_IWOTH 0000002 /* W for other */ 153#define S_IXOTH 0000001 /* X for other */ 154 155#define S_ISUID 0004000 /* set user id on execution */ 156#define S_ISGID 0002000 /* set group id on execution */ 157#define S_ISVTX 0001000 /* sticky bit */ 158.Ed 159.Pp 160The non-standard 161.Dv S_ISTXT 162is a synonym for 163.Dv S_ISVTX . 164.Pp 165The 166.Fx 167VM system totally ignores the sticky bit 168.Pq Dv S_ISVTX 169for executables. 170On UFS-based file systems (FFS, LFS) the sticky 171bit may only be set upon directories. 172.Pp 173If mode 174.Dv S_ISVTX 175(the `sticky bit') is set on a directory, 176an unprivileged user may not delete or rename 177files of other users in that directory. 178The sticky bit may be 179set by any user on a directory which the user owns or has appropriate 180permissions. 181For more details of the properties of the sticky bit, see 182.Xr sticky 7 . 183.Pp 184If mode ISUID (set UID) is set on a directory, 185and the MNT_SUIDDIR option was used in the mount of the file system, 186then the owner of any new files and sub-directories 187created within this directory are set 188to be the same as the owner of that directory. 189If this function is enabled, new directories will inherit 190the bit from their parents. 191Execute bits are removed from 192the file, and it will not be given to root. 193This behavior does not change the 194requirements for the user to be allowed to write the file, but only the eventual 195owner after it has been created. 196Group inheritance is not affected. 197.Pp 198This feature is designed for use on fileservers serving PC users via 199ftp, SAMBA, or netatalk. 200It provides security holes for shell users and as 201such should not be used on shell machines, especially on home directories. 202This option requires the SUIDDIR 203option in the kernel to work. 204Only UFS file systems support this option. 205For more details of the suiddir mount option, see 206.Xr mount 8 . 207.Pp 208Writing or changing the owner of a file 209turns off the set-user-id and set-group-id bits 210unless the user is the super-user. 211This makes the system somewhat more secure 212by protecting set-user-id (set-group-id) files 213from remaining set-user-id (set-group-id) if they are modified, 214at the expense of a degree of compatibility. 215.Sh RETURN VALUES 216.Rv -std 217.Sh ERRORS 218The 219.Fn chmod 220system call 221will fail and the file mode will be unchanged if: 222.Bl -tag -width Er 223.It Bq Er ENOTDIR 224A component of the path prefix is not a directory. 225.It Bq Er ENAMETOOLONG 226A component of a pathname exceeded 255 characters, 227or an entire path name exceeded 1023 characters. 228.It Bq Er ENOENT 229The named file does not exist. 230.It Bq Er EACCES 231Search permission is denied for a component of the path prefix. 232.It Bq Er ELOOP 233Too many symbolic links were encountered in translating the pathname. 234.It Bq Er EPERM 235The effective user ID does not match the owner of the file and 236the effective user ID is not the super-user. 237.It Bq Er EPERM 238The effective user ID is not the super-user, the effective user ID do match the 239owner of the file, but the group ID of the file does not match the effective 240group ID nor one of the supplementary group IDs. 241.It Bq Er EPERM 242The named file has its immutable or append-only flag set, see the 243.Xr chflags 2 244manual page for more information. 245.It Bq Er EROFS 246The named file resides on a read-only file system. 247.It Bq Er EFAULT 248The 249.Fa path 250argument 251points outside the process's allocated address space. 252.It Bq Er EIO 253An I/O error occurred while reading from or writing to the file system. 254.It Bq Er EINTEGRITY 255Corrupted data was detected while reading from the file system. 256.It Bq Er EFTYPE 257The effective user ID is not the super-user, the mode includes the sticky bit 258.Dv ( S_ISVTX ) , 259and path does not refer to a directory. 260.El 261.Pp 262The 263.Fn fchmod 264system call will fail if: 265.Bl -tag -width Er 266.It Bq Er EBADF 267The descriptor is not valid. 268.It Bq Er EINVAL 269The 270.Fa fd 271argument 272refers to a socket, not to a file. 273.It Bq Er EROFS 274The file resides on a read-only file system. 275.It Bq Er EIO 276An I/O error occurred while reading from or writing to the file system. 277.It Bq Er EINTEGRITY 278Corrupted data was detected while reading from the file system. 279.El 280.Pp 281In addition to the 282.Fn chmod 283errors, 284.Fn fchmodat 285fails if: 286.Bl -tag -width Er 287.It Bq Er EBADF 288The 289.Fa path 290argument does not specify an absolute path and the 291.Fa fd 292argument is neither 293.Fa AT_FDCWD 294nor a valid file descriptor open for searching. 295.It Bq Er EINVAL 296The value of the 297.Fa flag 298argument is not valid. 299.It Bq Er ENOTDIR 300The 301.Fa path 302argument is not an absolute path and 303.Fa fd 304is neither 305.Dv AT_FDCWD 306nor a file descriptor associated with a directory. 307.It Bq Er ENOTCAPABLE 308.Fa path 309is an absolute path, 310or contained a ".." component leading to a 311directory outside of the directory hierarchy specified by 312.Fa fd , 313and the process is in capability mode. 314.It Bq Er ENOTCAPABLE 315The 316.Dv AT_BENEATH 317flag was provided to 318.Fn fchmodat , 319and the absolute 320.Fa path 321does not have its tail fully contained under the topping directory, 322or the relative 323.Fa path 324escapes it. 325.El 326.Sh SEE ALSO 327.Xr chmod 1 , 328.Xr chflags 2 , 329.Xr chown 2 , 330.Xr open 2 , 331.Xr stat 2 , 332.Xr sticky 7 333.Sh STANDARDS 334The 335.Fn chmod 336system call is expected to conform to 337.St -p1003.1-90 , 338except for the return of 339.Er EFTYPE . 340The 341.Dv S_ISVTX 342bit on directories is expected to conform to 343.St -susv3 . 344The 345.Fn fchmodat 346system call is expected to conform to 347.St -p1003.1-2008 . 348.Sh HISTORY 349The 350.Fn chmod 351function appeared in 352.At v1 . 353The 354.Fn fchmod 355system call appeared in 356.Bx 4.2 . 357The 358.Fn lchmod 359system call appeared in 360.Fx 3.0 . 361The 362.Fn fchmodat 363system call appeared in 364.Fx 8.0 . 365