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man: reorder description of nspawn --console 

The default value was described at the end of two long paragraphs.
Make the first para self contained, and move the description of --console=pipe
into the second para.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek 2019-10-23 10:13:30 +02:00
parent dce66ffedb
commit 7a25ba554a
1 changed files with 25 additions and 23 deletions
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48
man/systemd-nspawn.xml
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@ -1296,30 +1296,32 @@
<varlistentry>
<term><option>--console=</option><replaceable>MODE</replaceable></term>
<listitem><para>Configures how to set up standard input, output and error output for the container payload, as
well as the <filename>/dev/console</filename> device for the container. Takes one of
<option>interactive</option>, <option>read-only</option>, <option>passive</option> or <option>pipe</option>. If
<option>interactive</option> a pseudo-TTY is allocated and made available as <filename>/dev/console</filename>
in the container. It is then bi-directionally connected to the standard input and output passed to
<command>systemd-nspawn</command>. <option>read-only</option> is similar but only the output of the container
is propagated and no input from the caller is read. In <option>passive</option> mode a pseudo TTY is allocated,
but it is not connected anywhere. Finally, in <option>pipe</option> mode no pseudo TTY is allocated, but the
passed standard input, output and error output file descriptors are passed on — as they are — to the container
payload. In this mode <filename>/dev/console</filename> will not exist in the container. Note that in this mode
the container payload generally cannot be a full init system as init systems tend to require
<filename>/dev/console</filename> to be available. On the other hand, in this mode container invocations can be
used within shell pipelines. This is because intermediary pseudo TTYs do not permit independent bidirectional
propagation of the end-of-file (EOF) condition, which is necessary for shell pipelines to work
correctly.</para>
<para>Note that the <option>pipe</option> mode should be used carefully, as passing arbitrary file descriptors
to less trusted container payloads might open up unwanted interfaces for access by the container payload. For
example, if a passed file descriptor refers to a TTY of some form, APIs such as <constant>TIOCSTI</constant>
may be used to synthesize input that might be used for escaping the container. Hence <option>pipe</option> mode
should only be used if the payload is sufficiently trusted or when the standard input/output/error output file
descriptors are known safe, for example pipes. Defaults to <option>interactive</option> if
<listitem><para>Configures how to set up standard input, output and error output for the container
payload, as well as the <filename>/dev/console</filename> device for the container. Takes one of
<option>interactive</option>, <option>read-only</option>, <option>passive</option>, or
<option>pipe</option>. If <option>interactive</option>, a pseudo-TTY is allocated and made available
as <filename>/dev/console</filename> in the container. It is then bi-directionally connected to the
standard input and output passed to <command>systemd-nspawn</command>. <option>read-only</option> is
similar but only the output of the container is propagated and no input from the caller is read. If
<option>passive</option>, a pseudo TTY is allocated, but it is not connected anywhere. Finally, in
<option>pipe</option> mode no pseudo TTY is allocated, but the standard input, output and error
output file descriptors passed to <command>systemd-nspawn</command> are passed on — as they are — to
the container payload, see the following paragraph. Defaults to <option>interactive</option> if
<command>systemd-nspawn</command> is invoked from a terminal, and <option>read-only</option>
otherwise.</para></listitem>
otherwise.</para>
<para>In <option>pipe</option> mode, <filename>/dev/console</filename> will not exist in the
container. This means that the container payload generally cannot be a full init system as init
systems tend to require <filename>/dev/console</filename> to be available. On the other hand, in this
mode container invocations can be used within shell pipelines. This is because intermediary pseudo
TTYs do not permit independent bidirectional propagation of the end-of-file (EOF) condition, which is
necessary for shell pipelines to work correctly. <emphasis>Note that the <option>pipe</option> mode
should be used carefully</emphasis>, as passing arbitrary file descriptors to less trusted container
payloads might open up unwanted interfaces for access by the container payload. For example, if a
passed file descriptor refers to a TTY of some form, APIs such as <constant>TIOCSTI</constant> may be
used to synthesize input that might be used for escaping the container. Hence <option>pipe</option>
mode should only be used if the payload is sufficiently trusted or when the standard
input/output/error output file descriptors are known safe, for example pipes.</para></listitem>
</varlistentry>
<varlistentry>