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persistence.conf.de.5
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persistence.conf.de.5
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.\"*******************************************************************
.\"
.\" This file was generated with po4a. Translate the source file.
.\"
.\"*******************************************************************
.TH LIVE\-BOOT conf 11.03.2013 4.0~a9\-1 "Live Systems Project"
.SH NAME
\fBpersistence.conf\fP \- Configuration file for persistence media in live\-boot
.SH DESCRIPTION
If live\-boot probes a persistence volume with the label (or GPT name, or
file name, but from now on we will just say "label") "persistence", that
volume's persistence is fully customizable through the \fBpersistence.conf\fP
file stored on the root of its file system. Any such labeled volume must
have such a file, or it will be ignored.
.PP
The format of \fBpersistence.conf\fP allows empty lines and lines starting with
a "#" (used for comments), both which will be ignored. A so called "custom
mount" has the format:
.PP
.RS
\fIDIR\fP [\fIOPTION\fP]...
.RE
.PP
which roughly translates to "make \fIDIR\fP persistence in the way described by
the list of \fIOPTION\fPs".
.PP
For each custom mount \fIDIR\fP must be an absolute path that cannot contain
white spaces or the special . and .. path components, and cannot be /live
(or any of its sub\-directories). Once activated all changes (file deletion,
creation and modification) to \fIDIR\fP on the live file system are stored
persistently into a path equivalent to \fIDIR\fP on the persistence media,
called the source directory. The default way to achieve persistence is to
simply bind\-mount the corresponding source directory to \fIDIR\fP, but this can
be changed through the use of \fIOPTION\fPs.
.PP
All custom mounts will be done in an order so that no two custom mounts can
"hide" each other. For instance, if we have the two \fIDIR\fP:s /a and /a/b it
would always be the case that /a is mounted first, then /a/b. This remains
true no matter how the lines in \fBpersistence.conf\fP are ordered, or if
several \fBpersistence.conf\fP files on different persistence media are used at
the same time. However, it is forbidden for custom mounts to have their
source directory inside the source directory of another custom mount, so the
source directories that are auto\-created by live\-boot does not support
"nested" mounts like /a and /a/b on the same media. In this case you must
use the \fBsource\fP option (see below) to make sure that they are stored in
different source directories.
.PP
When a source directory doesn't exist on the persistence media for a certain
custom mount, it will be created automatically, and permissions and
ownership will be optimistically set according to \fIDIR\fP. It will also be
bootstrapped by copying the contents of the \fIDIR\fP into its source directory
on the persistence media. The bootstrapping will not happen when the \fBlink\fP
or \fBunion\fP options are used (see below).
.SH OPTIONS
Custom mounts defined in \fBpersistence.conf\fP accept the following options in
a coma\-separated list:
.IP \fBsource\fP=\fIPATH\fP 4
When given, store the persistence changes into \fIPATH\fP on the persistence
media. \fIPATH\fP must be a relative path (with respect to the persistence
media root) that cannot contain white spaces or the special . or .. path
components, with the exception that it can be just . which means the
persistence media root. This option is mostly relevant if you want to nest
custom mounts, which otherwise would cause errors, or if you want to make
the whole media root available (similar to the now deprecated \fBhome\-rw\fP
type of persistence).
.PP
The following options are mutually exclusive (only the last given one will
be in effect):
.IP \fBbind\fP 4
Bind\-mount the source directory to \fIDIR\fP. This is the default.
.IP \fBlink\fP 4
Create the directory structure of the source directory on the persistence
media in \fIDIR\fP and create symbolic links from the corresponding place in
\fIDIR\fP to each file in the source directory. Existing files or directories
with the same name as any link will be overwritten. Note that deleting the
links in \fIDIR\fP will only remove the link, not the corresponding file in the
source; removed links will reappear after a reboot. To permanently add or
delete a file one must do so directly in the source directory.
.IP
Effectively \fBlink\fP will make only files already in the source directory
persistent, not any other files in \fIDIR\fP. These files must be manually
added to the source directory to make use of this option, and they will
appear in \fIDIR\fP in addition to files already there. This option is useful
when only certain files need to be persistent, not the whole directory
they're in, e.g. some configuration files in a user's home directory.
.IP \fBunion\fP 4
Save the rw branch of a union on the persistence media, so only the changes
are stored persistently. This can potentially reduce disk usage compared to
bind\-mounts, and will not hide files added to the read\-only media. One
caveat is that the union will use \fIDIR\fP from the image's read\-only file
system, not the real file system root, so files created after boot (e.g. by
live\-config) will not appear in the union. This option will use the union
file system specified by live\-boot's \fBunion\fP boot parameter, but is not
supported with \fBunion=unionmount\fP.
.SH DIRECTORIES
.IP \fB/live/persistence\fP 4
All persistence volumes will be mounted here (in a directory corresponding
to the device name). The \fBpersistence.conf\fP file can easily be edited
through this mount, as well as any source directories (which is especially
practical for custom mounts using the \fBlink\fP option).
.SH EXAMPLES
Let's say we have a persistence volume \fIVOL\fP with the a \fBpersistence.conf\fP
file containing the following four lines (numbered for ease of reference):
.TP 7
1.
/home/user1 link,source=config\-files/user1
.TP
2.
/home/user2 link,source=config\-files/user2
.TP
3.
/home
.TP
4.
/usr union
.PP
The corresponding source directories are:
.TP 7
1.
\fIVOL\fP/config\-files/user1 (but it would be \fIVOL\fP/home/user1 without the
\fBsource\fP option)
.TP
2.
\fIVOL\fP/config\-files/user2 (but it would be \fIVOL\fP/home/user2 without the
\fBsource\fP option)
.TP
3.
\fIVOL\fP/home
.TP
4.
\fIVOL\fP/usr
.PP
It was necessary to set the \fBsource\fP options for 1 and 2, since they
otherwise would become nested with 3's source, which is invalid.
.PP
Line 3 will be taken care of before line 1 and 2 in order to prevent custom
mounts 1 and 2 from being hidden by 3. When line 3 is handled, \fIVOL\fP/home
is simply bind\-mounted on /home. To illustrate what happens for lines 1 and
2, let's say that the following files exist:
.TP 7
a.
\fIVOL\fP/config\-files/user1/.emacs
.TP
b.
\fIVOL\fP/config\-files/user2/.bashrc
.TP
c.
\fIVOL\fP/config\-files/user2/.ssh/config
.PP
Then the following links and directories will be created:
.TP 7
Link:
/home/user1/.emacs \-> \fIVOL\fP/config\-files/user1/.emacs (from a)
.TP
Link:
/home/user2/.bashrc \-> \fIVOL\fP/config\-files/user2/.bashrc (from b)
.TP
Dir:
/homea/user2/.ssh (from c)
.TP
Link:
/home/user2/.ssh/config \-> \fIVOL\fP/config\-files/user2/.ssh/config (from
c)
.PP
One could argue, though, that lines 1 and 2 in the example
\fBpersistence.conf\fP file above are unnecessary since line 3 already would
make all of /home persistent. The \fBlink\fP option is intended for situations
where you don't want a complete directory to be persistent, only certain
files in it or its sub\-directories.
.PP
Line 4 can be mounted at any time since its \fIDIR\fP (and source directory) is
completely disjoint from all the other custom mounts. When mounted,
\fIVOL\fP/usr will be the rw branch due to the \fBunion\fP option, and will only
contain the difference compared to the underlying read\-only file
system. Hence packages could be installed into /usr with great space\-wise
efficiency compared to bind\-mounts, since in the latter case all of /usr
would have to be copied into \fIVOL\fP/usr during the initial bootstrap.
.SH "SEE ALSO"
\fIlive\-boot\fP(7)
.PP
\fIlive\-build\fP(7)
.PP
\fIlive\-config\fP(7)
.PP
\fIlive\-tools\fP(7)
.SH HOMEPAGE
More information about live\-boot and the Live Systems project can be found
on the homepage at <\fIhttp://live\-systems.org/\fP> and in the manual
at <\fIhttp://live\-systems.org/manual/\fP>.
.SH BUGS
Bugs can be reported by submitting a bugreport for the live\-boot package in
the Bug Tracking System at <\fIhttp://bugs.debian.org/\fP> or by
writing a mail to the Live Systems mailing list at
<\fIdebian\-live@lists.debian.org\fP>.
.SH AUTHOR
live\-boot was written by Daniel Baumann <\fImail@daniel\-baumann.ch\fP>.