mount.txt

操作系统文件管理

							1999-01-31
							Emil Brink

			About auto mounting

1. INTRODUCTION
In gentoo version 0.9.23, support for auto mounting was added. This
is (like much other in gentoo) most useful on personal systems,
and has *ONLY* been tested under Linux. If you're having trouble
with mounting on other platforms, don't be surprised.
	This file gives a brief description of the mount support,
and how to configure it.


2. MOUNT MODES
A "mode" variable determines when gentoo will attempt to mount
directories. There are three modes available:
	By default, the mode is "never", which causes auto mounting
to be disabled. In this mode, gentoo will never mount anything no
matter what you do.
	In the next mode, gentoo will only attempt to mount when
you access a directory either by double-clicking it in a pane, or
by activating a shortcut pointing at the directory in question.
	In the last mode, gentoo will attempt to do a mount each
time you access a directory. This is perhaps the most comfortable
way of doing it, but also the slowest.


3. MOUNT/UNMOUNT COMMANDS
Since there is no portable way of mounting file systems, and the
mount(2) system call available on Linux is privileged, gentoo uses
the normal user-level mount(8) command to do the mounting. For the
exact same reasons, unmounting is done by calling the umount(8)
shell command.
	gentoo assumes that it can mount a file system on a mount-
point X by issuing the command "mount X", and that it can unmount
in the same way. If this isn't true on your system, you must write
glue scripts that have this interface. You don't need to call your
scripts "mount" and "umount", however, since the actual command
names (but not the simple "calling convention") is configurable.


4. AVAILABLE FILE SYSTEM DATABASE
gentoo obtains information about which directories are mount points
by reading in a (set of) system database(s). On Linux systems, this
database is stored in the "/etc/fstab" file. This file contains
information about file systems, including which system mounts under
directory. gentoo buffers this information and uses it to determine
if a directory being accessed is a mount point.
	As hinted above, gentoo is not actually limited to reading
just one of these files. You can specify any number of files, sep-
arated by colons, in the "fstab" path (on the Paths config tab).


5. MOUNTED FILE SYSTEMS DATABASE
Before issuing a mount command to mount a new file system, gentoo
needs to check if the file system is already mounted. This is to
avoid errors from the "mount" command.
	This check is done through another (set of) system data-
base(s). On Linux, "/etc/mtab" holds the relevant information. The
default is to use "/proc/mounts", however, since the latter is
both faster to access, and more up to date.
	The time required to scan this database (which is not
buffered, since you can mount/unmount outside of gentoo) is the
reason why the middle mounting mode exists: it reduces the number
of accesses that are considered for mounting, thereby saving time.
	Again, you are not limited to just one of these databases
either. You can specify a list of files, separated by colons, in
the "mtab" path (on the Paths tab in the config window).


6. CONFIGURING THE MOUNTING
There's a tab labeled "Mounting" in the configuration window. This
tab holds most of the controls needed to configure the mounting.
The tab is split into two frames: one for setting the mode, and
the other for setting various flags.
	You set the mode by clicking on one of the radio buttons
in the mode frame. If you set the mounting mode to "Never", the
options frame is disabled to indicate that they are not used.
	Below the mode frame is another frame, labeled "Mount
Options". It contains some additional controls that let you fine-
tune the behavior of the mounting.
	The text entry fields labeled "Mount Command" and "Unmount
Command" let you specify the names of the shell commands used to
mount and unmount file systems. These commands should take, as a
single argument, the name of the *mount point*, not the file
system! Also, you must specify the path (e.g. "/bin/mount") too.
	The check button labeled "Only Mount on Toplevel Dirs?"
enables a little optimization: if checked, gentoo will not mount
on a directory that has more than 2 hard links to it. This means
any directory that contains another directory will never be con-
sidered as a possible mount point.
	The "Use Command Error Dialog?" option makes gentoo grab
any error output by the mount/unmount commands and show it in a
dialog. If not checked, errors will appear in the shell window.
	The "Unmount at Exit?" option makes gentoo call the un-
mount command on all file systems it mounted. This is recommended.

NOTE:	in addition to the stuff on the "Mounting" tab, you
	must also set the "fstab" and "mtab" paths (on the "Paths"
	tab, shockingly enough) to sensible values. For a Linux
	system, fstab="/etc/fstab" and mtab="/proc/mounts" works
	well.