.\" $NetBSD: chmod.2,v 1.7 1995/02/27 12:32:06 cgd Exp $ .\" .\" 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. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the University of .\" California, Berkeley and its contributors. .\" 4. 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 June 4, 1993 .Dt CHMOD 2 .Os BSD 4 .Sh NAME .Nm chmod , .Nm fchmod , .Nm fchmodat .Nd change mode of file .Sh SYNOPSIS .Fd #include .Fd #include .Ft int .Fo chmod .Fa "const char *path" .Fa "mode_t mode" .Fc .Ft int .Fo fchmod .Fa "int fildes" .Fa "mode_t mode" .Fc .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 fildes . .Fn chmod verifies that the process owner (user) either owns the file specified by .Fa path (or .Fa fildes ) , or is the super-user. .Pp The .Fn fchmodat is equivalent to .Fn chmod except in the case where .Fa path specifies a relative path. In this case the file to be changed is determined relative to the directory associated with the file descriptor .Fa fd instead of the current working directory. The values for the .Fa flag are constructed by a bitwise-inclusive OR of flags from the following list, defined in .In fcntl.h : .Bl -tag -width indent .It Dv AT_SYMLINK_NOFOLLOW If .Fa path names a symbolic link, then the mode of the symbolic link is changed. .El .Pp If .Fn fchmodat is passed the special value .Dv AT_FDCWD in the .Fa fd parameter, the current working directory is used. If also .Fa flag is zero, the behavior is identical to a call to .Fn chmod . A mode is created from .Em or'd permission bit masks defined in .Aq Pa sys/stat.h : .Bd -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 /* save swapped text even after use */ .Ed .Pp The .Dv ISVTX (the .Em sticky bit ) indicates to the system which executable files are shareable (the default) and the system maintains the program text of the files in the swap area. The sticky bit may only be set by the super user on shareable executable files. .Pp If mode .Dv ISVTX (the `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. For more details of the properties of the sticky bit, see .Xr sticky 8 . .Pp Writing or changing the owner of 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 Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and .Va errno is set to indicate the error. .Sh ERRORS The .Fn chmod system call will fail and the file mode will be unchanged if: .Bl -tag -width Er .\" ========== .It Bq Er EACCES Search permission is denied for a component of the path prefix. .\" ========== .It Bq Er EFAULT .Fa Path points outside the process's allocated address space. .\" ========== .It Bq Er EINTR Its execution was interrupted by a signal. .\" ========== .It Bq Er EIO An I/O error occurred while reading from or writing to the file system. .\" ========== .It Bq Er ELOOP Too many symbolic links were encountered in translating the pathname. This is taken to be indicative of a looping symbolic link. .\" ========== .It Bq Er ENAMETOOLONG A component of a pathname exceeded .Dv {NAME_MAX} characters, or an entire path name exceeded .Dv {PATH_MAX} characters. .\" ========== .It Bq Er ENOENT The named file does not exist. .\" ========== .It Bq Er ENOTDIR A component of the path prefix is not a directory. .\" ========== .It 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. .\" ========== .It Bq Er EROFS The named file resides on a read-only file system. .El .Pp .Fn fchmod will fail if: .Bl -tag -width Er .\" ========== .It Bq Er EBADF .Fa fildes is not a valid file descriptor. .\" ========== .It Bq Er EINVAL .Fa fildes refers to a socket, not to a file. .\" ========== .It Bq Er EINVAL .Fa mode is not a valid file mode. .\" ========== .It Bq Er EINTR Its execution was interrupted by a signal. .\" ========== .It Bq Er EIO An I/O error occurred while reading from or writing to the file system. .\" ========== .It 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. .\" ========== .It Bq Er EROFS The file resides on a read-only file system. .El .Pp In addition to the .Fn chmod errors, .Fn fchmodat fails if: .Bl -tag -width Er .It Bq Er EBADF The .Fa path argument does not specify an absolute path and the .Fa fd argument is neither .Fa AT_FDCWD nor a valid file descriptor open for searching. .It Bq Er EINVAL The value of the .Fa flag argument is not valid. .It Bq Er ENOTDIR The .Fa path argument is not an absolute path and .Fa fd is neither .Dv AT_FDCWD nor a file descriptor associated with a directory. .El .Sh LEGACY SYNOPSIS .Fd #include .Fd #include .Pp The include file .In sys/types.h is necessary. .Sh SEE ALSO .Xr chmod 1 , .Xr chown 2 , .Xr open 2 , .Xr stat 2 , .Xr compat 5 , .Xr sticky 8 .Sh STANDARDS The .Fn chmod function is expected to conform to .St -p1003.1-88 . The .Fn fchmodat function is expected to conform to POSIX.1-2008 . .Sh HISTORY The .Fn fchmod function call appeared in .Bx 4.2 . The .Fn fchmodat system call appeared in OS X 10.10