Understanding read-only bits

What a read-only bit is  

The read-only bit is a bit that is set on a file-by-file basis to reflect whether a file is writable or read-only.

Which clients set a read-only bit  

CIFS clients that use MS-DOS and Windows can set a per-file read-only bit. NFS clients do not set a per-file read-only bit because NFS clients do not have any protocol operations that use a per-file read-only bit.

When Data ONTAP can set a read-only bit  

Data ONTAP sets a read-only bit on a file when a CIFS client that uses MS-DOS or Windows creates that file. Data ONTAP can also set a read-only bit when a file is shared between NFS clients and CIFS clients because some software, when used by NFS clients and CIFS clients, requires that the read-only bit reflects whether the file is writable.

How Data ONTAP keeps appropriate permissions on shared files  

For Data ONTAP to keep the appropriate read and write permissions on a file shared between NFS clients and CIFS clients, it treats the read-only bit according to the following rules:

• Any file with the read-only bit turned on is treated, for all NFS operations, as if it had no write permission bits turned on.
• If a file has at least one write permission bit turned on and an NFS client turns off all write permission bits, the filer turns on the read-only bit for that file.
• If a file has no write permission bits turned on and an NFS client turns on any write permission bit, the filer turns off the read-only bit for that file.
• If the read-only bit for a file is turned on and an NFS client attempts to discover permission bits for the file, the permission bits for the file are not sent to the NFS client; instead, the filer sends the permission bits to the NFS client with the write permission bits masked off.
• If the read-only bit for a file is turned on and a CIFS client turns the read-only bit off, the filer turns on the owner's write permission bit for the file.
• Files with the read-only bit turned on are writable only by root.

  Note
  Changes to a file's permissions appear immediately on CIFS clients, but might not appear immediately on NFS clients if the NFS client enables attribute caching.

Deleting files with the read-only bit set  

Windows does not allow you to delete a file with the read-only bit set. Some multiprotocol source control applications require UNIX delete semantics; files for these applications with the read-only bit set also cannot be deleted.

To allow deletion of files using UNIX delete semantics when the read-only bit is set, complete the following step.

options cifs.perm_check_ro_del_ok on

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Part No. 210-00323
File: multi4.htm
Last updated: 01/15/03 15:46:09