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@(#)chmod.2 8.1 (Berkeley) 6/4/93
$FreeBSD: stable/10/lib/libc/sys/chmod.2 221845 2011-05-13 16:29:57Z pluknet $
.Dd April 10, 2008 .Dt CHMOD 2 .Os .Sh NAME .Nm chmod , .Nm fchmod , .Nm lchmod , .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 fchmod "int fd" "mode_t mode" .Ft int .Fn lchmod "const char *path" "mode_t mode" .Ft int .Fn fchmodat "int fd" "const char *path" "mode_t mode" "int flag" .Sh DESCRIPTION The file permission bits of the file named specified by .Fa path or referenced by the file descriptor .Fa fd are changed to .Fa mode . The .Fn chmod system call verifies that the process owner (user) either owns the file specified by .Fa path (or .Fa fd ) , or is the super-user. The .Fn chmod system call follows symbolic links to operate on the target of the link rather than the link itself.
p The .Fn lchmod system call is similar to .Fn chmod but does not follow symbolic links.
p The .Fn fchmodat is equivalent to either .Fn chmod or .Fn lchmod depending on the .Fa flag 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 n fcntl.h : l -tag -width indent t Dv AT_SYMLINK_NOFOLLOW If .Fa path names a symbolic link, then the mode of the symbolic link is changed. .El
p 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 .
p A mode is created from .Em or'd permission bit masks defined in n sys/stat.h :
p 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 */ #ifndef __BSD_VISIBLE #define S_ISTXT 0001000 /* sticky bit */ #endif .Ed
p The .Fx VM system totally ignores the sticky bit
q Dv ISTXT for executables. On UFS-based file systems (FFS, LFS) the sticky bit may only be set upon directories.
p If mode .Dv ISTXT (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 7 .
p If mode ISUID (set UID) is set on a directory, and the MNT_SUIDDIR option was used in the mount of the file system, then the owner of any new files and sub-directories created within this directory are set to be the same as the owner of that directory. If this function is enabled, new directories will inherit the bit from their parents. Execute bits are removed from the file, and it will not be given to root. This behavior does not change the requirements for the user to be allowed to write the file, but only the eventual owner after it has been created. Group inheritance is not affected.
p This feature is designed for use on fileservers serving PC users via ftp, SAMBA, or netatalk. It provides security holes for shell users and as such should not be used on shell machines, especially on home directories. This option requires the SUIDDIR option in the kernel to work. Only UFS file systems support this option. For more details of the suiddir mount option, see .Xr mount 8 .
p 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 .Rv -std .Sh ERRORS The .Fn chmod system call will fail and the file mode will be unchanged if: l -tag -width Er t Bq Er ENOTDIR A component of the path prefix is not a directory. t Bq Er ENAMETOOLONG A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters. t Bq Er ENOENT The named file does not exist. t Bq Er EACCES Search permission is denied for a component of the path prefix. t Bq Er ELOOP Too many symbolic links were encountered in translating the pathname. 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. t Bq Er EPERM The effective user ID is not the super-user, the effective user ID do match the owner of the file, but the group ID of the file does not match the effective group ID nor one of the supplementary group IDs. t Bq Er EPERM The named file has its immutable or append-only flag set, see the .Xr chflags 2 manual page for more information. t Bq Er EROFS The named file resides on a read-only file system. t Bq Er EFAULT The .Fa path argument points outside the process's allocated address space. t Bq Er EIO An I/O error occurred while reading from or writing to the file system. t Bq Er EFTYPE The effective user ID is not the super-user, the mode includes the sticky bit .Dv ( S_ISVTX ) , and path does not refer to a directory. .El
p The .Fn fchmod system call will fail if: l -tag -width Er t Bq Er EBADF The descriptor is not valid. t Bq Er EINVAL The .Fa fd argument refers to a socket, not to a file. t Bq Er EROFS The file resides on a read-only file system. t Bq Er EIO An I/O error occurred while reading from or writing to the file system. .El
p In addition to the .Fn chmod errors, .Fn fchmodat fails if: l -tag -width Er t 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. t Bq Er EINVAL The value of the .Fa flag argument is not valid. t 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 SEE ALSO .Xr chmod 1 , .Xr chflags 2 , .Xr chown 2 , .Xr open 2 , .Xr stat 2 , .Xr sticky 7 .Sh STANDARDS The .Fn chmod system call is expected to conform to .St -p1003.1-90 , except for the return of .Er EFTYPE and the use of .Dv S_ISTXT . The .Fn fchmodat system call follows The Open Group Extended API Set 2 specification. .Sh HISTORY The .Fn chmod function appeared in .At v7 . The .Fn fchmod system call appeared in x 4.2 . The .Fn lchmod system call appeared in .Fx 3.0 . The .Fn fchmodat system call appeared in .Fx 8.0 .