.\" Copyright (c) 1980, 1991 Regents of the University of California. .\" All rights reserved. .\" .\" %sccs.include.redist.man% .\" .\" @(#)chmod.2 6.6 (Berkeley) %G% .\" .Dd .Dt CHMOD 2 .Os BSD 4 .Sh NAME .Nm chmod , .Nm fchmod .Nd change mode of file .Sh SYNOPSIS .Fd #include .Ft int .Fn chmod "const char *path" "mode_t mode" .Ft int .Fn fchmod "int fd" "mode_t mode" .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 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 .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 .Fn Chmod will fail and the file mode will be unchanged if: .Bl -tag -width Er .It Bq Er ENOTDIR A component of the path prefix is not a directory. .It Bq Er EINVAL The pathname contains a character with the high-order bit set. .It Bq Er ENAMETOOLONG A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters. .It Bq Er ENOENT The named file does not exist. .It Bq Er EACCES Search permission is denied for a component of the path prefix. .It Bq Er ELOOP Too many symbolic links were encountered in translating the pathname. .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. .It Bq Er EFAULT .Fa Path points outside the process's allocated address space. .It Bq Er EIO An I/O error occurred while reading from or writing to the file system. .El .Pp .Fn Fchmod will fail if: .Bl -tag -width Er .It Bq Er EBADF The descriptor is not valid. .It Bq Er EINVAL .Fa Fd refers to a socket, not to a file. .It Bq Er EROFS The file resides on a read-only file system. .It Bq Er EIO An I/O error occurred while reading from or writing to the file system. .El .Sh SEE ALSO .Xr chmod 1 , .Xr open 2 , .Xr chown 2 , .Xr stat 2 , .Xr sticky 8 .Sh STANDARDS .Fn Chmod is expected to conform to IEEE Std 1003.1-1988 .Pq Dq Tn POSIX . .Sh HISTORY The .Fn fchmod function call appeared in .Bx 4.2 .