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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 November 11, 2018 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.El 113.Pp 114If 115.Fn fchmodat 116is passed the special value 117.Dv AT_FDCWD 118in the 119.Fa fd 120parameter, the current working directory is used. 121If also 122.Fa flag 123is zero, the behavior is identical to a call to 124.Fn chmod . 125.Pp 126A mode is created from 127.Em or'd 128permission bit masks 129defined in 130.In sys/stat.h : 131.Pp 132.Bd -literal -offset indent -compact 133#define S_IRWXU 0000700 /* RWX mask for owner */ 134#define S_IRUSR 0000400 /* R for owner */ 135#define S_IWUSR 0000200 /* W for owner */ 136#define S_IXUSR 0000100 /* X for owner */ 137 138#define S_IRWXG 0000070 /* RWX mask for group */ 139#define S_IRGRP 0000040 /* R for group */ 140#define S_IWGRP 0000020 /* W for group */ 141#define S_IXGRP 0000010 /* X for group */ 142 143#define S_IRWXO 0000007 /* RWX mask for other */ 144#define S_IROTH 0000004 /* R for other */ 145#define S_IWOTH 0000002 /* W for other */ 146#define S_IXOTH 0000001 /* X for other */ 147 148#define S_ISUID 0004000 /* set user id on execution */ 149#define S_ISGID 0002000 /* set group id on execution */ 150#define S_ISVTX 0001000 /* sticky bit */ 151.Ed 152.Pp 153The non-standard 154.Dv S_ISTXT 155is a synonym for 156.Dv S_ISVTX . 157.Pp 158The 159.Fx 160VM system totally ignores the sticky bit 161.Pq Dv S_ISVTX 162for executables. 163On UFS-based file systems (FFS, LFS) the sticky 164bit may only be set upon directories. 165.Pp 166If mode 167.Dv S_ISVTX 168(the `sticky bit') is set on a directory, 169an unprivileged user may not delete or rename 170files of other users in that directory. 171The sticky bit may be 172set by any user on a directory which the user owns or has appropriate 173permissions. 174For more details of the properties of the sticky bit, see 175.Xr sticky 7 . 176.Pp 177If mode ISUID (set UID) is set on a directory, 178and the MNT_SUIDDIR option was used in the mount of the file system, 179then the owner of any new files and sub-directories 180created within this directory are set 181to be the same as the owner of that directory. 182If this function is enabled, new directories will inherit 183the bit from their parents. 184Execute bits are removed from 185the file, and it will not be given to root. 186This behavior does not change the 187requirements for the user to be allowed to write the file, but only the eventual 188owner after it has been created. 189Group inheritance is not affected. 190.Pp 191This feature is designed for use on fileservers serving PC users via 192ftp, SAMBA, or netatalk. 193It provides security holes for shell users and as 194such should not be used on shell machines, especially on home directories. 195This option requires the SUIDDIR 196option in the kernel to work. 197Only UFS file systems support this option. 198For more details of the suiddir mount option, see 199.Xr mount 8 . 200.Pp 201Writing or changing the owner of a file 202turns off the set-user-id and set-group-id bits 203unless the user is the super-user. 204This makes the system somewhat more secure 205by protecting set-user-id (set-group-id) files 206from remaining set-user-id (set-group-id) if they are modified, 207at the expense of a degree of compatibility. 208.Sh RETURN VALUES 209.Rv -std 210.Sh ERRORS 211The 212.Fn chmod 213system call 214will fail and the file mode will be unchanged if: 215.Bl -tag -width Er 216.It Bq Er ENOTDIR 217A component of the path prefix is not a directory. 218.It Bq Er ENAMETOOLONG 219A component of a pathname exceeded 255 characters, 220or an entire path name exceeded 1023 characters. 221.It Bq Er ENOENT 222The named file does not exist. 223.It Bq Er EACCES 224Search permission is denied for a component of the path prefix. 225.It Bq Er ELOOP 226Too many symbolic links were encountered in translating the pathname. 227.It Bq Er EPERM 228The effective user ID does not match the owner of the file and 229the effective user ID is not the super-user. 230.It Bq Er EPERM 231The effective user ID is not the super-user, the effective user ID do match the 232owner of the file, but the group ID of the file does not match the effective 233group ID nor one of the supplementary group IDs. 234.It Bq Er EPERM 235The named file has its immutable or append-only flag set, see the 236.Xr chflags 2 237manual page for more information. 238.It Bq Er EROFS 239The named file resides on a read-only file system. 240.It Bq Er EFAULT 241The 242.Fa path 243argument 244points outside the process's allocated address space. 245.It Bq Er EIO 246An I/O error occurred while reading from or writing to the file system. 247.It Bq Er EFTYPE 248The effective user ID is not the super-user, the mode includes the sticky bit 249.Dv ( S_ISVTX ) , 250and path does not refer to a directory. 251.El 252.Pp 253The 254.Fn fchmod 255system call will fail if: 256.Bl -tag -width Er 257.It Bq Er EBADF 258The descriptor is not valid. 259.It Bq Er EINVAL 260The 261.Fa fd 262argument 263refers to a socket, not to a file. 264.It Bq Er EROFS 265The file resides on a read-only file system. 266.It Bq Er EIO 267An I/O error occurred while reading from or writing to the file system. 268.El 269.Pp 270In addition to the 271.Fn chmod 272errors, 273.Fn fchmodat 274fails if: 275.Bl -tag -width Er 276.It Bq Er EBADF 277The 278.Fa path 279argument does not specify an absolute path and the 280.Fa fd 281argument is neither 282.Fa AT_FDCWD 283nor a valid file descriptor open for searching. 284.It Bq Er EINVAL 285The value of the 286.Fa flag 287argument is not valid. 288.It Bq Er ENOTDIR 289The 290.Fa path 291argument is not an absolute path and 292.Fa fd 293is neither 294.Dv AT_FDCWD 295nor a file descriptor associated with a directory. 296.It Bq Er ENOTCAPABLE 297.Fa path 298is an absolute path, 299or contained a ".." component leading to a 300directory outside of the directory hierarchy specified by 301.Fa fd , 302and the process is in capability mode. 303.It Bq Er ENOTCAPABLE 304The 305.Dv AT_BENEATH 306flag was provided to 307.Fn fchmodat , 308and the absolute 309.Fa path 310does not have its tail fully contained under the topping directory, 311or the relative 312.Fa path 313escapes it. 314.El 315.Sh SEE ALSO 316.Xr chmod 1 , 317.Xr chflags 2 , 318.Xr chown 2 , 319.Xr open 2 , 320.Xr stat 2 , 321.Xr sticky 7 322.Sh STANDARDS 323The 324.Fn chmod 325system call is expected to conform to 326.St -p1003.1-90 , 327except for the return of 328.Er EFTYPE . 329The 330.Dv S_ISVTX 331bit on directories is expected to conform to 332.St -susv3 . 333The 334.Fn fchmodat 335system call is expected to conform to 336.St -p1003.1-2008 . 337.Sh HISTORY 338The 339.Fn chmod 340function appeared in 341.At v1 . 342The 343.Fn fchmod 344system call appeared in 345.Bx 4.2 . 346The 347.Fn lchmod 348system call appeared in 349.Fx 3.0 . 350The 351.Fn fchmodat 352system call appeared in 353.Fx 8.0 . 354