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.TH posixovl 1 "2010-12-07" "posixovl" "posixovl"
.SH Name
.PP
posixovl \(em The POSIX Overlay Filesystem
.SH Syntax
.PP
\fBmount.posixovl\fP [\fB\-F\fP] [\fB\-S\fP \fIsource_dir\fP] \fItarget_dir\fP
[\fB\-\-\fP \fIfuse_opts\fP]
.SH Description
.PP
posixovl provides a filesystem view that supports various POSIX operations
while using an otherwise incapable lower filesystem. Filesystems of various
degrees of POSIXness can be utilitzed. VFAT is a common denominator when it
comes to cross-compatibility, though NTFS \(em its features are unused in
Linux \(em would be another possibility. Secondly, potent native POSIX-style
filesystems can also be used, though the actual use of doing that remains to
be discovered.
.SH Options
.PP
If no source directory is given, the target directory specifies both source
and target (mountpoint), yielding an "overmount".
.TP
\fB\-F\fP
Disable permission and ownership checks on the lower filesystem. Normally these
would be used to check for POSIX filesystems mounted inside a non-POSIX
tree. (For example, where /vfat is vfat, and /vfat/xfs is a POSIX-behaving
filesystem.)
.SH Supported operations
.PP
posixovl will emulate the following calls if the lower filesystem is incapable
of supporting these operations:
.IP \(bu 4
chmod
.IP \(bu 4
chown
.IP \(bu 4
hard links
.IP \(bu 4
mkfifo
.IP \(bu 4
mknod
.IP \(bu 4
symbolic links
.PP
The following currently only work in passthrough mode (when using a lower
filesystem that already supports these):
.IP \(bu 4
Linux ACLs/xattrs
.PP
Missing suppot:
.IP \(bu 4
Case-sensitivity
.SH Notes
.PP
Using posixovl on an already POSIX-behaving filesystem (e.g. XFS) incurs some
issues, since detecting whether a path is POSIX behaving or not is difficult.
Hence, the following decision was made:
.IP \(bu 4
permissions will be set to the default permissions (see below) unless a HCB
(hidden control block, the metadata files for posixovl) is found that can
override these
.IP \(bu 4
all lower-level files will be operated on/created with the user who inititated
the mount
.PP
If no HCB exists for a file or directory, the default permissions are 644 and
755, respectively. The owner and group of the inode will be the owner/group of
the real file.
.PP
Each non-regular, non-directory virtual file will have a zero-size real file.
(Simplifies handling, and makes it apprarent the object exists when using other
OS.)
.PP
`df` will show:
.nf
$ df -Tah
Filesystem Type Size Used Avail Use% Mounted on
/dev/hda5 vfat 5.9G 2.1G 3.9G 35% /windows/D
posix-overlay(/windows/D)
fuse.posixovl 5.9G 2.1G 3.9G 35% /windows/D
.fi
.PP
In general, posixovl does not handle case-insensitivity of the underlying
filesystem (in case of vfat, for example). If you create a file "X0" on vfat,
it is usually lowercased to "x0", which may break some software, namely X.org.
In order to make vfat behave more POSIX-like, the following mount options are
recommended:
.PP
$ mount -t vfat /dev/hda1 /windows/D -o check=s,shortname=mixed
.SH Authors
.PP
posixovl and this manpage were written by Jan Engelhardt.
.PP
Development of posixovl was sponsored by Slax (http://www.slax.org/).
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