Copyright (c) 1980, 1991, 1993
The Regents of the University of California. All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
3. Neither the name of the University nor the names of its contributors
may be used to endorse or promote products derived from this software
without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.
@(#)chmod.2 8.1 (Berkeley) 6/4/93
.Dd November 20, 2021 .Dt CHMOD 2 .Os .Sh NAME .Nm chmod , .Nm lchmod , .Nm fchmod , .Nm fchmodat .Nd change mode of file .Sh LIBRARY .Lb libc .Sh SYNOPSIS n sys/stat.h .Ft int .Fn chmod "const char *path" "mode_t mode" .Ft int .Fn lchmod "const char *path" "mode_t mode" .Ft int .Fn fchmod "int fd" "mode_t mode" n sys/stat.h n fcntl.h .Ft int .Fn fchmodat "int fd" "const char *path" "mode_t mode" "int flag" .Sh DESCRIPTION The function .Fn chmod sets the file permission bits of the file specified by the pathname .Fa path to .Fa mode . .Fn fchmod sets the permission bits of the specified file descriptor .Fa fd . .Fn lchmod is like .Fn chmod except in the case where the named file is a symbolic link, in which case .Fn lchmod sets the permission bits of the link, while .Fn chmod sets the bits of the file the link references.
p
.Fn fchmodat
works the same way as
.Fn chmod
(or
.Fn lchmod
if
.Dv AT_SYMLINK_NOFOLLOW
is set in
.Fa flag )
except if
.Fa path
is relative.
In that case, it is looked up from a directory whose file
descriptor was passed as
.Fa fd .
Search permission is required on this directory.
(These alternatives await a decision about the semantics of O_SEARCH)
Search permission is required on this directory
except if
.Fa fd
was opened with the
.Dv O_SEARCH
flag.
- or -
This file descriptor must have been opened with the
.Dv O_SEARCH
flag.
.Fa fd
except if that file descriptor was opened with the
.Dv O_SEARCH
flag.
.Fa fd
can be set to
.Dv AT_FDCWD
in order to specify the current directory.
p .Fn chmod verifies that the process owner (user) either owns the file specified by .Fa path (or .Fa fd ) , or is the super-user. A mode is created from .Em or'd permission bit masks defined in n sys/stat.h : d -literal -offset indent -compact #define S_IRWXU 0000700 /* RWX mask for owner */ #define S_IRUSR 0000400 /* R for owner */ #define S_IWUSR 0000200 /* W for owner */ #define S_IXUSR 0000100 /* X for owner */ #define S_IRWXG 0000070 /* RWX mask for group */ #define S_IRGRP 0000040 /* R for group */ #define S_IWGRP 0000020 /* W for group */ #define S_IXGRP 0000010 /* X for group */ #define S_IRWXO 0000007 /* RWX mask for other */ #define S_IROTH 0000004 /* R for other */ #define S_IWOTH 0000002 /* W for other */ #define S_IXOTH 0000001 /* X for other */ #define S_ISUID 0004000 /* set user id on execution */ #define S_ISGID 0002000 /* set group id on execution */ #define S_ISVTX 0001000 /* sticky bit */ .Ed
p The mode .Dv ISVTX (the .Sq sticky bit ) can be set on regular files, but has no effect. For historical reasons this can be done only by the super-user.
p If mode .Dv ISVTX (the .Sq sticky bit ) is set on a directory, an unprivileged user may not delete or rename files of other users in that directory. The sticky bit may be set by any user on a directory which the user owns or has appropriate permissions.
p For more information about the history and properties of the sticky bit, see .Xr sticky 7 .
p Changing the owner of a file turns off the set-user-id and set-group-id bits; writing to a file turns off the set-user-id and set-group-id bits unless the user is the super-user. This makes the system somewhat more secure by protecting set-user-id (set-group-id) files from remaining set-user-id (set-group-id) if they are modified, at the expense of a degree of compatibility. .Sh RETURN VALUES .Rv -std chmod lchmod fchmod fchmodat .Sh ERRORS .Fn chmod , .Fn lchmod and .Fn fchmodat will fail and the file mode will be unchanged if: l -tag -width Er t Bq Er EACCES Search permission is denied for a component of the path prefix. t Bq Er EFAULT .Fa path points outside the process's allocated address space. t Bq Er EFTYPE The effective user ID is not the super-user, the .Fa mode includes the sticky bit
q Dv S_ISVTX , and .Fa path does not refer to a directory. t Bq Er EIO An I/O error occurred while reading from or writing to the file system. t Bq Er ELOOP Too many symbolic links were encountered in translating the pathname. t Bq Er ENAMETOOLONG A component of a pathname exceeded rq Dv NAME_MAX characters, or an entire path name exceeded rq Dv PATH_MAX characters. t Bq Er ENOENT The named file does not exist. t Bq Er ENOTDIR A component of the path prefix is not a directory. t Bq Er EPERM The effective user ID does not match the owner of the file and the effective user ID is not the super-user; or the mode includes the setgid bit
q Dv S_ISGID but the file's group is neither the effective group ID nor is it in the group access list. t Bq Er EROFS The named file resides on a read-only file system. .El
p In addition, .Fn fchmodat will fail if: l -tag -width Er t Bq Er EBADF .Fa path does not specify an absolute path and .Fa fd is neither .Dv AT_FDCWD nor a valid file descriptor open for reading or searching. t Bq Er ENOTDIR .Fa path is not an absolute path and .Fa fd is a file descriptor associated with a non-directory file. .El
p .Fn fchmod will fail if: l -tag -width Er t Bq Er EBADF The descriptor is not valid. t Bq Er EFTYPE The effective user ID is not the super-user, the .Fa mode includes the sticky bit
q Dv S_ISVTX , and .Fa fd does not refer to a directory. t Bq Er EINVAL .Fa fd refers to a socket, not to a file. t Bq Er EIO An I/O error occurred while reading from or writing to the file system. t Bq Er EPERM The effective user ID does not match the owner of the file and the effective user ID is not the super-user; or the mode includes the setgid bit
q Dv S_ISGID but the file's group is neither the effective group ID nor is it in the group access list. t Bq Er EROFS The file resides on a read-only file system. .El .Sh SEE ALSO .Xr chmod 1 , .Xr chflags 2 , .Xr chown 2 , .Xr open 2 , .Xr stat 2 , .Xr getmode 3 , .Xr setmode 3 , .Xr sticky 7 , .Xr symlink 7 .Sh STANDARDS The .Fn chmod function conforms to .St -p1003.1-90 . The .Fn fchmod function conforms to .St -xpg4.2 . The .Fn fchmodat function conforms to .St -p1003.1-2008 . .Sh HISTORY The .Fn chmod function call appeared in .At v1 . The .Fn fchmod function call appeared in x 4.2 . The .Fn lchmod function call appeared in .Nx 1.3 .
Indexes created Sat Sep 20 22:09:52 GMT 2025