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 lengtha | Permissions | Directories | Hard links | Soft links | Decompression on read |
---|---|---|---|---|---|---|---|---|---|
Image | No | No | No | 255 | Yes | No | No | No | No |
RAMb | Yes | Yes | Yes | 255 | Yes | No | No | No | No |
ETFS | Yes | Yes | Yes | 91 | Yes | Yes | No | Yes | No |
QNX 4 | Yes | Yes | Yes | 48c | Yes | Yes | Yes | Yes | No |
Power-Safe | Yes | Yes | Yes | 510 | Yes | Yes | Yes | Yes | No |
DOS | Yesd | Yes | No | 8.3e | No | Yes | No | No | No |
NTFS | Yes | Yes | Yes | 755 | No | Yes | No | No | Yes |
CD-ROM | Yesf | Yesf | Yesf | 207g | Yesf | Yes | No | Yesf | No |
UDF | Yes | Yes | Yes | 254 | Yes | Yes | No | No | No |
HFS, HFS Plus | Yes | Yes | Yes | 255h | Yes | Yes | Yes | Yes | No |
FFS3 | No | Yes | Yes | 255 | Yes | Yes | No | Yes | No |
NFS | Yes | Yes | Yes | —i | Yesi | Yes | Yesi | Yesi | No |
CIFS | No | Yes | No | —i | Yesi | 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 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 505 if .longfilenames is enabled; otherwise, 48.
d VFAT or FAT32 (Windows 95 or later).
e 255-character filename lengths used by VFAT or FAT32 (Windows 95 or later).
f With Rock Ridge extensions.
g 103 characters with Joliet extensions; 255 with Rock Ridge extensions.
h 31 on HFS.
i Limited by the remote filesystem.