Filesystem limitations

POSIX defines the set of services a filesystem must provide. However, not all filesystems are capable of delivering all those services.

Filesystem	Access date	Modification date	Status change date	Filename length^a	Permissions	Directories	Hard links	Soft links	Decompression on read
Image	No	No	No	255	Yes	No	No	No	No
RAM^b	Yes	Yes	Yes	255	Yes	No	No	No	No
ETFS	Yes	Yes	Yes	91	Yes	Yes	No	Yes	No
Power-Safe	Yes	Yes	Yes	510	Yes	Yes	Yes	Yes	No
DOS	Yes^c	Yes	No	8.3^d	No	Yes	No	No	No
NTFS	Yes	Yes	Yes	755	No	Yes	No	No	Yes
UDF	Yes	Yes	Yes	254	Yes	Yes	No	No	No
HFS, HFS Plus	Yes	Yes	Yes	255^e	Yes	Yes	Yes	Yes	No
FFS3	No	Yes	Yes	255	Yes	Yes	No	Yes	No
NFS	Yes	Yes	Yes	—^f	Yes^f	Yes	Yes^f	Yes^f	No
CIFS	No	Yes	No	—^f	Yes^f	Yes	No	No	No
Ext2	Yes	Yes	Yes	255	Yes	Yes	Yes	Yes	No

^a Our internal representation for file names is UTF-8, which uses a variable number of bytes per character. Many on-disk formats instead use UCS2, which is a fixed number (2 bytes). Thus a length limit in characters may be 1, 2, or 3 times that number in bytes, as we convert from on-disk to OS representation. The lengths for the Power-Safe and EXT2 filesystems are in bytes; those for UDF and DOS/VFAT are in characters.

^b The RAM “filesystem” (/dev/shmem) isn't really a filesystem; it's a window onto the shared memory names that has some filesystem-like characteristics. See “Builtin RAM disk” later in this chapter.

^c VFAT or FAT32 (Windows 95 or later).

^d 255-character filename lengths used by VFAT or FAT32 (e.g., Windows 95).

^e 31 on HFS.

^f Limited by the remote filesystem.