documentation/linux-fat-permissions - wine - Git at Google

 This document describes how FAT and VFAT file system permissions work
 in Linux with a focus on configuring them for Wine.

 Introduction
 ------------
 Linux is able to access DOS and Windows file systems using either the
 FAT (older 8.3 DOS filesystems) or VFAT (newer Windows 95 or later
 long filename filesystems) modules.  Mounted FAT or VFAT filesystems
 provide the primary means for which existing applications and their
 data are accessed through Wine for dual boot (Linux + Windows)
 systems.

 Wine maps mounted FAT filesystems, such as "/c", to driver letters,
 such as "c:", as indicated by the wine.conf file.  The following
 excerpt from a wine.conf file does this:
     [Drive C]
     Path=/c
     Type=hd

 Although VFAT filesystems are preferable to FAT filesystems for their
 long filename support the term "FAT" will be used throughout the
 remainder of this document to refer to FAT filesystems and their
 derivatives.  Also, "/c" will be used as the FAT mount point in
 examples throughout this document.

 Most modern Linux distributions either detect or allow existing FAT
 file systems to be configured so that can be mounted, in a location
 such as /c, either persistently (on bootup) or on an as needed basis.
 In either case, by default, the permissions will probably be configured
 so that they look something like:
     ~>cd /c
     /c>ls -l
     -rwxr-xr-x   1 root     root           91 Oct 10 17:58 autoexec.bat
     -rwxr-xr-x   1 root     root          245 Oct 10 17:58 config.sys
     drwxr-xr-x  41 root     root        16384 Dec 30  1998 windows
 where all the files are owned by "root", are in the "root" group and
 are only writable by "root" (755 permissions).  This is restrictive in
 that it requires that Wine be run as root in order for applications to
 be able to write to any part of the filesystem.

 There three major approaches to overcoming the restrictive permissions
 mentioned in the previous paragraph:
     1) Run Wine as root
     2) Mount the FAT filesystem with less restrictive permissions
     3) Shadow the FAT filesystem by completely or partially copying it
 Each approach will be discusses in the following "Running Wine as
 root", "Mounting FAT filesystems" and "Shadowing FAT filesystems"
 sections.

 Running Wine as root
 --------------------
 Running Wine as root is the easiest and most thorough way of giving
 applications that Wine runs unrestricted access to FAT files systems.
 Running wine as root also allows applications to do things unrelated
 to FAT filesystems, such as listening to ports that are less than
 1024.  Running Wine as root is dangerous since there is no limit to
 what the application can do to the system.

 Mounting FAT filesystems
 ------------------------
 The FAT filesystem can be mounted with permissions less restrictive
 than the default.  This can be done by either changing the user that
 mounts the FAT filesystem or by explicitly changing the permissions
 that the FAT filesystem is mounted with.  The permissions are
 inherited from the process that mounts the FAT filesystem.  Since the
 process that mounts the FAT filesystem is usually a startup script
 running as root the FAT filesystem inherits root's permissions.  This
 results in the files on the FAT filesystem having permissions similar
 to files created by root.  For example:
     ~>whoami
     root
     ~>touch root_file
     ~>ls -l root_file
     -rw-r--r--   1 root     root            0 Dec 10 00:20 root_file

 which matches the owner, group and permissions of files seen on the
 FAT filesystem except for the missing 'x's.  The permissions on the
 FAT filesystem can be changed by changing root's umask (unset
 permissions bits).  For example:
     ~>umount /c
     ~>umask
     022
     ~>umask 073
     ~>mount /c
     ~>cd /c
     /c>ls -l
     -rwx---r--   1 root     root           91 Oct 10 17:58 autoexec.bat
     -rwx---r--   1 root     root          245 Oct 10 17:58 config.sys
     drwx---r--  41 root     root        16384 Dec 30  1998 windows
 Mounting the FAT filesystem with a umask of 000 gives all users
 complete control over the it.
 Explicitly specifying the permissions of the FAT filesystem when it is
 mounted provides additional control.  There are three mount options
 that are relevant to FAT permissions: "uid", "gid" and "umask".  They
 can each be specified when the filesystem is manually mounted.  For
 example:
     ~>umount /c
     ~>mount -o uid=500 -o gid=500 -o umask=002 /c
     ~>cd /c
     /c>ls -l
     -rwxrwxr-x   1 sle      sle            91 Oct 10 17:58 autoexec.bat
     -rwxrwxr-x   1 sle      sle           245 Oct 10 17:58 config.sys
     drwxrwxr-x  41 sle      sle         16384 Dec 30  1998 windows
 which gives "sle" complete control over /c.  The options listed above
 can be made permanent by adding them to the /etc/fstab file:
     ~>grep /c /etc/fstab
     /dev/hda1  /c  vfat  uid=500,gid=500,umask=002,exec,dev,suid,rw 1 1
 Note that the umask of 002 is common in the user private group file
 permission scheme.  On FAT file systems this umask assures that all
 files are fully accessible by all users in the specified group (gid).

 Shadowing FAT filesystems
 -------------------------
 Shadowing provides a finer granularity of control.  Parts of the
 original FAT filesystem can be copied so that the application can
 safely work with those copied parts while the application continue to
 directly read the remaining parts.  This is done with symbolic links.
 For example, consider a system where an application named "AnApp" must
 be able to read and write to the c:\windows and c:\AnApp directories
 as well as have read access to the entire FAT filesystem.  On this
 system the FAT filesystem has default permissions which should not be
 changed for security reasons or can not be changed due to lack of root
 access.  On this system a shadow directory might be set up in the
 following manner:
     ~>cd /
     />mkdir c_shadow
     />cd c_shadow
     /c_shadow>ln -s /c_/* .
     /c_shadow>rm windows AnApp
     /c_shadow>cp -R /c_/{windows,AnApp} .
     /c_shadow>chmod -R 777 windows AnApp
     /c_shadow>perl -p -i -e 's|/c$|/c_shadow|g' /usr/local/etc/wine.conf
 The above gives everyone complete read and write access to the
 "windows" and "AnApp" directories while only root has write access to
 all other directories.
 ---
 Steven Elliott (elliotsl@mindspring.com)
	This document describes how FAT and VFAT file system permissions work
	in Linux with a focus on configuring them for Wine.

	Introduction
	------------
	Linux is able to access DOS and Windows file systems using either the
	FAT (older 8.3 DOS filesystems) or VFAT (newer Windows 95 or later
	long filename filesystems) modules. Mounted FAT or VFAT filesystems
	provide the primary means for which existing applications and their
	data are accessed through Wine for dual boot (Linux + Windows)
	systems.

	Wine maps mounted FAT filesystems, such as "/c", to driver letters,
	such as "c:", as indicated by the wine.conf file. The following
	excerpt from a wine.conf file does this:
	[Drive C]
	Path=/c
	Type=hd

	Although VFAT filesystems are preferable to FAT filesystems for their
	long filename support the term "FAT" will be used throughout the
	remainder of this document to refer to FAT filesystems and their
	derivatives. Also, "/c" will be used as the FAT mount point in
	examples throughout this document.

	Most modern Linux distributions either detect or allow existing FAT
	file systems to be configured so that can be mounted, in a location
	such as /c, either persistently (on bootup) or on an as needed basis.
	In either case, by default, the permissions will probably be configured
	so that they look something like:
	~>cd /c
	/c>ls -l
	-rwxr-xr-x 1 root root 91 Oct 10 17:58 autoexec.bat
	-rwxr-xr-x 1 root root 245 Oct 10 17:58 config.sys
	drwxr-xr-x 41 root root 16384 Dec 30 1998 windows
	where all the files are owned by "root", are in the "root" group and
	are only writable by "root" (755 permissions). This is restrictive in
	that it requires that Wine be run as root in order for applications to
	be able to write to any part of the filesystem.

	There three major approaches to overcoming the restrictive permissions
	mentioned in the previous paragraph:
	1) Run Wine as root
	2) Mount the FAT filesystem with less restrictive permissions
	3) Shadow the FAT filesystem by completely or partially copying it
	Each approach will be discusses in the following "Running Wine as
	root", "Mounting FAT filesystems" and "Shadowing FAT filesystems"
	sections.

	Running Wine as root
	--------------------
	Running Wine as root is the easiest and most thorough way of giving
	applications that Wine runs unrestricted access to FAT files systems.
	Running wine as root also allows applications to do things unrelated
	to FAT filesystems, such as listening to ports that are less than
	1024. Running Wine as root is dangerous since there is no limit to
	what the application can do to the system.

	Mounting FAT filesystems
	------------------------
	The FAT filesystem can be mounted with permissions less restrictive
	than the default. This can be done by either changing the user that
	mounts the FAT filesystem or by explicitly changing the permissions
	that the FAT filesystem is mounted with. The permissions are
	inherited from the process that mounts the FAT filesystem. Since the
	process that mounts the FAT filesystem is usually a startup script
	running as root the FAT filesystem inherits root's permissions. This
	results in the files on the FAT filesystem having permissions similar
	to files created by root. For example:
	~>whoami
	root
	~>touch root_file
	~>ls -l root_file
	-rw-r--r-- 1 root root 0 Dec 10 00:20 root_file

	which matches the owner, group and permissions of files seen on the
	FAT filesystem except for the missing 'x's. The permissions on the
	FAT filesystem can be changed by changing root's umask (unset
	permissions bits). For example:
	~>umount /c
	~>umask
	022
	~>umask 073
	~>mount /c
	~>cd /c
	/c>ls -l
	-rwx---r-- 1 root root 91 Oct 10 17:58 autoexec.bat
	-rwx---r-- 1 root root 245 Oct 10 17:58 config.sys
	drwx---r-- 41 root root 16384 Dec 30 1998 windows
	Mounting the FAT filesystem with a umask of 000 gives all users
	complete control over the it.
	Explicitly specifying the permissions of the FAT filesystem when it is
	mounted provides additional control. There are three mount options
	that are relevant to FAT permissions: "uid", "gid" and "umask". They
	can each be specified when the filesystem is manually mounted. For
	example:
	~>umount /c
	~>mount -o uid=500 -o gid=500 -o umask=002 /c
	~>cd /c
	/c>ls -l
	-rwxrwxr-x 1 sle sle 91 Oct 10 17:58 autoexec.bat
	-rwxrwxr-x 1 sle sle 245 Oct 10 17:58 config.sys
	drwxrwxr-x 41 sle sle 16384 Dec 30 1998 windows
	which gives "sle" complete control over /c. The options listed above
	can be made permanent by adding them to the /etc/fstab file:
	~>grep /c /etc/fstab
	/dev/hda1 /c vfat uid=500,gid=500,umask=002,exec,dev,suid,rw 1 1
	Note that the umask of 002 is common in the user private group file
	permission scheme. On FAT file systems this umask assures that all
	files are fully accessible by all users in the specified group (gid).

	Shadowing FAT filesystems
	-------------------------
	Shadowing provides a finer granularity of control. Parts of the
	original FAT filesystem can be copied so that the application can
	safely work with those copied parts while the application continue to
	directly read the remaining parts. This is done with symbolic links.
	For example, consider a system where an application named "AnApp" must
	be able to read and write to the c:\windows and c:\AnApp directories
	as well as have read access to the entire FAT filesystem. On this
	system the FAT filesystem has default permissions which should not be
	changed for security reasons or can not be changed due to lack of root
	access. On this system a shadow directory might be set up in the
	following manner:
	~>cd /
	/>mkdir c_shadow
	/>cd c_shadow
	/c_shadow>ln -s /c_/* .
	/c_shadow>rm windows AnApp
	/c_shadow>cp -R /c_/{windows,AnApp} .
	/c_shadow>chmod -R 777 windows AnApp
	/c_shadow>perl -p -i -e 's\|/c$\|/c_shadow\|g' /usr/local/etc/wine.conf
	The above gives everyone complete read and write access to the
	"windows" and "AnApp" directories while only root has write access to
	all other directories.
	---
	Steven Elliott (elliotsl@mindspring.com)