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Chapter 17. Access Control Lists > ACL Implementation Limits
17.7. ACL Implementation Limits
The various file-system implementations impose limits on the number of entries in an ACL:
On ext2, ext3, and ext4, the total number of ACLs on a file is governed by the requirement that the bytes in all of the names and values of a file’s extended attributes must be contained in a single logical disk block (Section 16.2). Each ACL entry requires 8 bytes, so that the maximum number of ACL entries for a file is somewhat less (because of some overhead for the name of the extended attribute for the ACL) than one-eighth of the block size. Thus, a 4096-byte block size allows for a maximum of around 500 ACL entries. (Kernels before 2.6.11 imposed an arbitrary limitation of 32 entries for ACLs on ext2 and ext3.)
On XFS, an ACL is limited to 25 entries.
On Reiserfs and JFS, ACLs can contain up to 8191 entries. This limit is a consequence of the size limitation (64 kB) imposed by the VFS on the value of an extended attribute (Section 16.2).
