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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 October 20, 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 starting directory. 107.El 108.Pp 109If 110.Fn fchmodat 111is passed the special value 112.Dv AT_FDCWD 113in the 114.Fa fd 115parameter, the current working directory is used. 116If also 117.Fa flag 118is zero, the behavior is identical to a call to 119.Fn chmod . 120.Pp 121A mode is created from 122.Em or'd 123permission bit masks 124defined in 125.In sys/stat.h : 126.Pp 127.Bd -literal -offset indent -compact 128#define S_IRWXU 0000700 /* RWX mask for owner */ 129#define S_IRUSR 0000400 /* R for owner */ 130#define S_IWUSR 0000200 /* W for owner */ 131#define S_IXUSR 0000100 /* X for owner */ 132 133#define S_IRWXG 0000070 /* RWX mask for group */ 134#define S_IRGRP 0000040 /* R for group */ 135#define S_IWGRP 0000020 /* W for group */ 136#define S_IXGRP 0000010 /* X for group */ 137 138#define S_IRWXO 0000007 /* RWX mask for other */ 139#define S_IROTH 0000004 /* R for other */ 140#define S_IWOTH 0000002 /* W for other */ 141#define S_IXOTH 0000001 /* X for other */ 142 143#define S_ISUID 0004000 /* set user id on execution */ 144#define S_ISGID 0002000 /* set group id on execution */ 145#define S_ISVTX 0001000 /* sticky bit */ 146.Ed 147.Pp 148The non-standard 149.Dv S_ISTXT 150is a synonym for 151.Dv S_ISVTX . 152.Pp 153The 154.Fx 155VM system totally ignores the sticky bit 156.Pq Dv S_ISVTX 157for executables. 158On UFS-based file systems (FFS, LFS) the sticky 159bit may only be set upon directories. 160.Pp 161If mode 162.Dv S_ISVTX 163(the `sticky bit') is set on a directory, 164an unprivileged user may not delete or rename 165files of other users in that directory. 166The sticky bit may be 167set by any user on a directory which the user owns or has appropriate 168permissions. 169For more details of the properties of the sticky bit, see 170.Xr sticky 7 . 171.Pp 172If mode ISUID (set UID) is set on a directory, 173and the MNT_SUIDDIR option was used in the mount of the file system, 174then the owner of any new files and sub-directories 175created within this directory are set 176to be the same as the owner of that directory. 177If this function is enabled, new directories will inherit 178the bit from their parents. 179Execute bits are removed from 180the file, and it will not be given to root. 181This behavior does not change the 182requirements for the user to be allowed to write the file, but only the eventual 183owner after it has been created. 184Group inheritance is not affected. 185.Pp 186This feature is designed for use on fileservers serving PC users via 187ftp, SAMBA, or netatalk. 188It provides security holes for shell users and as 189such should not be used on shell machines, especially on home directories. 190This option requires the SUIDDIR 191option in the kernel to work. 192Only UFS file systems support this option. 193For more details of the suiddir mount option, see 194.Xr mount 8 . 195.Pp 196Writing or changing the owner of a file 197turns off the set-user-id and set-group-id bits 198unless the user is the super-user. 199This makes the system somewhat more secure 200by protecting set-user-id (set-group-id) files 201from remaining set-user-id (set-group-id) if they are modified, 202at the expense of a degree of compatibility. 203.Sh RETURN VALUES 204.Rv -std 205.Sh ERRORS 206The 207.Fn chmod 208system call 209will fail and the file mode will be unchanged if: 210.Bl -tag -width Er 211.It Bq Er ENOTDIR 212A component of the path prefix is not a directory. 213.It Bq Er ENAMETOOLONG 214A component of a pathname exceeded 255 characters, 215or an entire path name exceeded 1023 characters. 216.It Bq Er ENOENT 217The named file does not exist. 218.It Bq Er EACCES 219Search permission is denied for a component of the path prefix. 220.It Bq Er ELOOP 221Too many symbolic links were encountered in translating the pathname. 222.It Bq Er EPERM 223The effective user ID does not match the owner of the file and 224the effective user ID is not the super-user. 225.It Bq Er EPERM 226The effective user ID is not the super-user, the effective user ID do match the 227owner of the file, but the group ID of the file does not match the effective 228group ID nor one of the supplementary group IDs. 229.It Bq Er EPERM 230The named file has its immutable or append-only flag set, see the 231.Xr chflags 2 232manual page for more information. 233.It Bq Er EROFS 234The named file resides on a read-only file system. 235.It Bq Er EFAULT 236The 237.Fa path 238argument 239points outside the process's allocated address space. 240.It Bq Er EIO 241An I/O error occurred while reading from or writing to the file system. 242.It Bq Er EFTYPE 243The effective user ID is not the super-user, the mode includes the sticky bit 244.Dv ( S_ISVTX ) , 245and path does not refer to a directory. 246.El 247.Pp 248The 249.Fn fchmod 250system call will fail if: 251.Bl -tag -width Er 252.It Bq Er EBADF 253The descriptor is not valid. 254.It Bq Er EINVAL 255The 256.Fa fd 257argument 258refers to a socket, not to a file. 259.It Bq Er EROFS 260The file resides on a read-only file system. 261.It Bq Er EIO 262An I/O error occurred while reading from or writing to the file system. 263.El 264.Pp 265In addition to the 266.Fn chmod 267errors, 268.Fn fchmodat 269fails if: 270.Bl -tag -width Er 271.It Bq Er EBADF 272The 273.Fa path 274argument does not specify an absolute path and the 275.Fa fd 276argument is neither 277.Fa AT_FDCWD 278nor a valid file descriptor open for searching. 279.It Bq Er EINVAL 280The value of the 281.Fa flag 282argument is not valid. 283.It Bq Er ENOTDIR 284The 285.Fa path 286argument is not an absolute path and 287.Fa fd 288is neither 289.Dv AT_FDCWD 290nor a file descriptor associated with a directory. 291.It Bq Er ENOTCAPABLE 292The 293.Dv AT_BENEATH 294flag was specified but 295.Fa path 296is not strictly relative to the starting directory. 297For example, 298.Fa path 299is absolute or includes a ".." component that escapes the starting directory. 300.El 301.Sh SEE ALSO 302.Xr chmod 1 , 303.Xr chflags 2 , 304.Xr chown 2 , 305.Xr open 2 , 306.Xr stat 2 , 307.Xr sticky 7 308.Sh STANDARDS 309The 310.Fn chmod 311system call is expected to conform to 312.St -p1003.1-90 , 313except for the return of 314.Er EFTYPE . 315The 316.Dv S_ISVTX 317bit on directories is expected to conform to 318.St -susv3 . 319The 320.Fn fchmodat 321system call is expected to conform to 322.St -p1003.1-2008 . 323.Sh HISTORY 324The 325.Fn chmod 326function appeared in 327.At v1 . 328The 329.Fn fchmod 330system call appeared in 331.Bx 4.2 . 332The 333.Fn lchmod 334system call appeared in 335.Fx 3.0 . 336The 337.Fn fchmodat 338system call appeared in 339.Fx 8.0 . 340