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 (disabled) or read-only (enabled).

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 can set 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. Some software, when used by NFS clients and CIFS clients, requires the read-only bit to be enabled.

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:

• NFS treats any file with the read-only bit enabled as if it has no write permission bits enabled.
• If an NFS client disables all write permission bits and at least one of those bits had previously been enabled, Data ONTAP enables the read-only bit for that file.
• If an NFS client enables any write permission bit, Data ONTAP disables the read-only bit for that file.
• If the read-only bit for a file is enabled and an NFS client attempts to discover permissions for the file, the permission bits for the file are not sent to the NFS client; instead, Data ONTAP sends the permission bits to the NFS client with the write permission bits masked.
• If the read-only bit for a file is enabled and a CIFS client disables the read-only bit, Data ONTAP enables the owner's write permission bit for the file.
• Files with the read-only bit enabled are writable only by root.

  Note
  Changes to a file's permissions take effect immediately on CIFS clients, but might not take effect 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 enabled. Some multiprotocol source control applications require UNIX delete semantics; files for these applications also cannot be deleted when the read-only bit is enabled.

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

options cifs.perm_check_ro_del_ok on

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Part No. 210-00473
File: multi4.htm
Last updated: 11/25/03 18:03:02