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doc: Discuss encrypted swap space. 

* doc/guix.texi (Preparing for Installation): Provide an example of how to
  set up (encrypted) swap space using a swap file.
  (operating-system Reference)[swap-devices]: Clarify that swap files are
  supported, too.
  (Mapped Devices): Explain how to use a mapped device with a swap file to
  encrypt swap space.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>
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Chris Marusich 2017-01-29 20:40:35 -08:00 committed by Ludovic Courtès
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@ -7063,6 +7063,26 @@ mkswap /dev/sda2
swapon /dev/sda2
@end example
Alternatively, you may use a swap file. For example, assuming that in
the new system you want to use the file @file{/swapfile} as a swap file,
you would run@footnote{This example will work for many types of file
systems (e.g., ext4). However, for copy-on-write file systems (e.g.,
btrfs), the required steps may be different. For details, see the
manual pages for @command{mkswap} and @command{swapon}.}:
@example
# This is 10 GiB of swap space. Adjust "count" to change the size.
dd if=/dev/zero of=/mnt/swapfile bs=1MiB count=10240
# For security, make the file readable and writable only by root.
chmod 600 /mnt/swapfile
mkswap /mnt/swapfile
swapon /mnt/swapfile
@end example
Note that if you have encrypted the root partition and created a swap
file in its file system as described above, then the encryption also
protects the swap file, just like any other file in that file system.
@node Proceeding with the Installation
@subsection Proceeding with the Installation
@ -7516,9 +7536,12 @@ A list of file systems. @xref{File Systems}.
@item @code{swap-devices} (default: @code{'()})
@cindex swap devices
A list of strings identifying devices to be used for ``swap space''
(@pxref{Memory Concepts,,, libc, The GNU C Library Reference Manual}).
For example, @code{'("/dev/sda3")}.
A list of strings identifying devices or files to be used for ``swap
space'' (@pxref{Memory Concepts,,, libc, The GNU C Library Reference
Manual}). For example, @code{'("/dev/sda3")} or @code{'("/swapfile")}.
It is possible to specify a swap file in a file system on a mapped
device, provided that the necessary device mapping and file system are
also specified. @xref{Mapped Devices} and @ref{File Systems}.
@item @code{users} (default: @code{%base-user-accounts})
@itemx @code{groups} (default: @var{%base-groups})
@ -7861,6 +7884,13 @@ and use it as follows:
(type luks-device-mapping))
@end example
@cindex swap encryption
It is also desirable to encrypt swap space, since swap space may contain
sensitive data. One way to accomplish that is to use a swap file in a
file system on a device mapped via LUKS encryption. In this way, the
swap file is encrypted because the entire device is encrypted.
@xref{Preparing for Installation,,Disk Partitioning}, for an example.
A RAID device formed of the partitions @file{/dev/sda1} and @file{/dev/sdb1}
may be declared as follows: