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

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Fixes: #7254
See: #2473
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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 <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 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>
<varlistentry> <varlistentry>

9
man/systemd.exec.xml
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@ -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 <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 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 <para>This setting defaults to the value set with
<option>DefaultStandardOutput=</option> in <option>DefaultStandardOutput=</option> in
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
which defaults to <option>journal</option>. Note that setting which defaults to <option>journal</option>. Note that setting
this parameter might result in additional dependencies to be 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>
<varlistentry> <varlistentry>