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This file is part of systemd.
Copyright 2014 Lennart Poettering
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<refentry id= "systemd-debug-generator" >
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<refentryinfo >
<title > systemd-debug-generator</title>
<productname > systemd</productname>
<authorgroup >
<author >
<contrib > Developer</contrib>
<firstname > Lennart</firstname>
<surname > Poettering</surname>
<email > lennart@poettering.net</email>
</author>
</authorgroup>
</refentryinfo>
<refmeta >
<refentrytitle > systemd-debug-generator</refentrytitle>
<manvolnum > 8</manvolnum>
</refmeta>
<refnamediv >
<refname > systemd-debug-generator</refname>
<refpurpose > Generator for enabling a runtime debug shell and
masking specific units at boot</refpurpose>
</refnamediv>
<refsynopsisdiv >
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<para > <filename > /usr/lib/systemd/system-generators/systemd-debug-generator</filename> </para>
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</refsynopsisdiv>
<refsect1 >
<title > Description</title>
<para > <filename > systemd-debug-generator</filename> is a generator
that reads the kernel command line and understands three
options:</para>
<para > If the <option > systemd.mask=</option> option is specified
and followed by a unit name, this unit is masked for the runtime,
similar to the effect of
<citerefentry > <refentrytitle > systemctl</refentrytitle> <manvolnum > 1</manvolnum> </citerefentry> 's
<command > mask</command> command. This is useful to boot with
certain units removed from the initial boot transaction for
debugging system startup. May be specified more than once.</para>
<para > If the <option > systemd.wants=</option> option is specified
and followed by a unit name, a start job for this unit is added to
the initial transaction. This is useful to start one or more
additional units at boot. May be specified more than once.</para>
util-lib: various improvements to kernel command line parsing
This improves kernel command line parsing in a number of ways:
a) An kernel option "foo_bar=xyz" is now considered equivalent to
"foo-bar-xyz", i.e. when comparing kernel command line option names "-" and
"_" are now considered equivalent (this only applies to the option names
though, not the option values!). Most of our kernel options used "-" as word
separator in kernel command line options so far, but some used "_". With
this change, which was a source of confusion for users (well, at least of
one user: myself, I just couldn't remember that it's systemd.debug-shell,
not systemd.debug_shell). Considering both as equivalent is inspired how
modern kernel module loading normalizes all kernel module names to use
underscores now too.
b) All options previously using a dash for separating words in kernel command
line options now use an underscore instead, in all documentation and in
code. Since a) has been implemented this should not create any compatibility
problems, but normalizes our documentation and our code.
c) All kernel command line options which take booleans (or are boolean-like)
have been reworked so that "foobar" (without argument) is now equivalent to
"foobar=1" (but not "foobar=0"), thus normalizing the handling of our
boolean arguments. Specifically this means systemd.debug-shell and
systemd_debug_shell=1 are now entirely equivalent.
d) All kernel command line options which take an argument, and where no
argument is specified will now result in a log message. e.g. passing just
"systemd.unit" will no result in a complain that it needs an argument. This
is implemented in the proc_cmdline_missing_value() function.
e) There's now a call proc_cmdline_get_bool() similar to proc_cmdline_get_key()
that parses booleans (following the logic explained in c).
f) The proc_cmdline_parse() call's boolean argument has been replaced by a new
flags argument that takes a common set of bits with proc_cmdline_get_key().
g) All kernel command line APIs now begin with the same "proc_cmdline_" prefix.
h) There are now tests for much of this. Yay!
2016-12-12 20:29:15 +03:00
<para > If the <option > systemd.debug_shell</option> option is
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specified, the debug shell service
<literal > debug-shell.service</literal> is pulled into the boot
transaction. It will spawn a debug shell on tty9 during early
system startup. Note that the shell may also be turned on
persistently by enabling it with
<citerefentry > <refentrytitle > systemctl</refentrytitle> <manvolnum > 1</manvolnum> </citerefentry> 's
<command > enable</command> command.</para>
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<para > <filename > systemd-debug-generator</filename> implements
<citerefentry > <refentrytitle > systemd.generator</refentrytitle> <manvolnum > 7</manvolnum> </citerefentry> .</para>
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</refsect1>
<refsect1 >
<title > See Also</title>
<para >
<citerefentry > <refentrytitle > systemd</refentrytitle> <manvolnum > 1</manvolnum> </citerefentry> ,
<citerefentry > <refentrytitle > systemctl</refentrytitle> <manvolnum > 1</manvolnum> </citerefentry> ,
<citerefentry > <refentrytitle > kernel-command-line</refentrytitle> <manvolnum > 7</manvolnum> </citerefentry>
</para>
</refsect1>
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</refentry>
