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	Yes	Yes	Yes	255	Yes	No	No	No	No
ETFS	Yes	Yes	Yes	91	Yes	Yes	No	Yes	No
QNX 4	Yes	Yes	Yes	48^b	Yes	Yes	Yes	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	No	255	No	Yes	No	No	Yes
CD-ROM	Yes^e	Yes^e	Yes^e	207^f	Yes^e	Yes	No	Yes^e	No
UDF	Yes	Yes	Yes	254	Yes	Yes	No	No	No
HFS	Yes	Yes	Yes	255^g	Yes	Yes	No	No	No
FFS3	No	Yes	Yes	255	Yes	Yes	No	Yes	Yes
NFS	Yes	Yes	Yes	—^h	Yes^h	Yes	Yes^h	Yes^h	No
CIFS	No	Yes	No	—^h	Yes^h	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 QNX 4, Power-Safe, and EXT2 filesystems are in bytes; those for UDF, CD/Joliet, and DOS/VFAT are in characters.

^b 505 if .longfilenames is enabled; otherwise, 48.

^c VFAT or FAT32 (e.g., Windows 95).

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

^e With Rock Ridge extensions.

^f 103 characters with Joliet extensions; 255 with Rock Ridge extensions.

^g 31 on HFS.

^h Limited by the remote filesystem.