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man: document > /dev/stderr pitfalls (#7317)

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Fixes: #7254
See: #2473
This commit is contained in:
Lennart Poettering 2017-11-14 10:51:09 +01:00 committed by Zbigniew Jędrzejewski-Szmek
parent 99c1401807
commit b0e8cec2dd
2 changed files with 16 additions and 3 deletions
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10
man/systemd-run.xml
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@ -244,7 +244,15 @@
<para>When both <option>--pipe</option> and <option>--pty</option> are used in combination the more appropriate
option is automatically determined and used. Specifically, when invoked with standard input, output and error
connected to a TTY <option>--pty</option> is used, and otherwise <option>--pipe</option>.</para></listitem>
connected to a TTY <option>--pty</option> is used, and otherwise <option>--pipe</option>.</para>
<para>When this option is used the original file descriptors <command>systemd-run</command> receives are passed
to the service processes as-is. If the service runs with different privileges than
<command>systemd-run</command>, this means the service might not be able to re-open the passed file
descriptors, due to normal file descriptor access restrictions. If the invoked process is a shell script that
uses the <command>echo "hello" > /dev/stderr</command> construct for writing messages to stderr, this might
cause problems, as this only works if stderr can be re-opened. To mitigate this use the construct <command>echo
"hello" >&amp;2</command> instead, which is mostly equivalent and avoids this pitfall.</para></listitem>
</varlistentry>
<varlistentry>

9
man/systemd.exec.xml
View File

@ -624,14 +624,19 @@
<para>If the standard output (or error output, see below) of a unit is connected to the journal, syslog or the
kernel log buffer, the unit will implicitly gain a dependency of type <varname>After=</varname> on
<filename>systemd-journald.socket</filename> (also see the "Implicit Dependencies" section above).</para>
<filename>systemd-journald.socket</filename> (also see the "Implicit Dependencies" section above). Also note
that in this case stdout (or stderr, see below) will be an <constant>AF_UNIX</constant> stream socket, and not
a pipe or FIFO that can be re-opened. This means when executing shell scripts the construct <command>echo
"hello" &gt; /dev/stderr</command> for writing text to stderr will not work. To mitigate this use the construct
<command>echo "hello" >&amp;2</command> instead, which is mostly equivalent and avoids this pitfall.</para>
<para>This setting defaults to the value set with
<option>DefaultStandardOutput=</option> in
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
which defaults to <option>journal</option>. Note that setting
this parameter might result in additional dependencies to be
added to the unit (see above).</para></listitem>
added to the unit (see above).</para>
</listitem>
</varlistentry>
<varlistentry>