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man: revise entry about specifying a file path (#3739)

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* Specifying a device node has an effect much larger than a simple shortcut
for a field/value match, so the original sentence is no longer a good way
to start the paragraph.
* Specifying a device node causes matches to be generated for all ancestor
devices of the device specified, not just its parents.
* Indicates that the path must be absolute, but that it may be a link.
* Eliminates a few typos.
This commit is contained in:
mulkieran 2016-07-19 23:15:22 -04:00 committed by Zbigniew Jędrzejewski-Szmek
parent dfc6109fcd
commit 13317a22e5
1 changed files with 20 additions and 12 deletions
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32
man/journalctl.xml
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@ -87,18 +87,26 @@
causes all matches before and after to be combined in a
disjunction (i.e. logical OR).</para>
<para>As shortcuts for a few types of field/value matches, file
paths may be specified. If a file path refers to an executable
file, this is equivalent to an <literal>_EXE=</literal> match
for the canonicalized binary path. Similarly, if a path refers
to a device node then match is added for the kernel name of the
device (<literal>_KERNEL_DEVICE=</literal>). Also, matches for the
kernel names of all the parent devices are added automatically.
Device node paths are not stable across reboots, therefore match
for the current boot id (<literal>_BOOT_ID=</literal>) is
always added as well. Note that only the log entries for
the existing device nodes maybe queried by providing path to
the device node.</para>
<para>It is also possible to filter the entries by specifying an
absolute file path as an argument. The file path may be a file or
a symbolic link and the file must exist at the time of the query. If a
file path refers to an executable binary, an <literal>_EXE=</literal>
match for the canonicalized binary path is added to the query. If a
file path refers to an executable script, a <literal>_COMM=</literal>
match for the script name is added to the query. If a file path
refers to a device node, <literal>_KERNEL_DEVICE=</literal> matches for
the kernel name of the device and for each of its ancestor devices is
added to the query. Symbolic links are dereferenced, kernel names are
synthesized, and parent devices are identified from the environment at
the time of the query. In general, a device node is the best proxy for
an actual device, as log entries do not usually contain fields that
identify an actual device. For the resulting log entries to be correct
for the actual device, the relevant parts of the environment at the time
the entry was logged, in particular the actual device corresponding to
the device node, must have been the same as those at the time of the
query. Because device nodes generally change their corresponding devices
across reboots, specifying a device node path causes the resulting
entries to be restricted to those from the current boot.</para>
<para>Additional constraints may be added using options
<option>--boot</option>, <option>--unit=</option>, etc., to