eudev/man/tmpfiles.d.xml
Dave Reisner 54693d9bfa tmpfiles: use write(2) for the 'w' action
This resolves problems with filesystems which do not implement the
aio_write file operation. In this case, the kernel will fall back using
a loop writing technique for each pointer in a received iovec. The
result is strange errors in dmesg such as:

[   31.855871] elevator: type  not found
[   31.856262] elevator: switch to
[   31.856262]  failed

It does not make sense to implement a synchronous aio_write method for
sysfs as this isn't a real filesystem where a reasonable use case for
using writev exists, nor is there an expectation that tmpfiles will be
used to write more data than can be reasonably written in a single write
syscall.

In addition, some sysfs attrs are currently buggy and will NOT reject
the second write with the newline, causing the sysfs value to be zeroed
out. This of course should be fixed in the kernel regardless of any
wrongdoing in userspace, but this simple change makes us immune to such
a bug.

This change means that we do not write a trailing newline by default, as
the expected use case of 'w' is for sysfs and procfs. In exchange, honor
C-style backslash escapes so that if the newline is really needed, the
user can add it.
2012-09-16 17:18:04 +02:00

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<?xml version="1.0"?>
<!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<refentry id="tmpfiles.d">
<refentryinfo>
<title>tmpfiles.d</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Documentation</contrib>
<firstname>Brandon</firstname>
<surname>Philips</surname>
<email>brandon@ifup.org</email>
</author>
</authorgroup>
</refentryinfo>
<refmeta>
<refentrytitle>tmpfiles.d</refentrytitle>
<manvolnum>5</manvolnum>
</refmeta>
<refnamediv>
<refname>tmpfiles.d</refname>
<refpurpose>Configuration for creation, deletion and
cleaning of volatile and temporary files</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename>/etc/tmpfiles.d/*.conf</filename></para>
<para><filename>/run/tmpfiles.d/*.conf</filename></para>
<para><filename>/usr/lib/tmpfiles.d/*.conf</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><command>systemd-tmpfiles</command> uses the
configuration files from the above directories to describe the
creation, cleaning and removal of volatile and
temporary files and directories which usually reside
in directories such as <filename>/run</filename>
or <filename>/tmp</filename>.</para>
</refsect1>
<refsect1>
<title>Configuration Format</title>
<para>Each configuration file shall be named in the
style of <filename>&lt;program&gt;.conf</filename>.
Files in <filename>/etc/</filename> override files
with the same name in <filename>/usr/lib/</filename>
and <filename>/run/</filename>. Files in
<filename>/run/</filename> override files with the same
name in <filename>/usr/lib/</filename>. Packages
should install their configuration files in
<filename>/usr/lib/</filename>. Files in
<filename>/etc/</filename> are reserved for the local
administrator, who may use this logic to override the
configuration files installed by vendor packages. All
configuration files are sorted by their filename in
alphabetical order, regardless in which of the
directories they reside, to guarantee that a specific
configuration file takes precedence over another file
with an alphabetically later name.</para>
<para>If the administrator wants to disable a
configuration file supplied by the vendor the
recommended way is to place a symlink to
<filename>/dev/null</filename> in
<filename>/etc/tmpfiles.d/</filename> bearing the
same file name.</para>
<para>The configuration format is one line per path
containing action, path, mode, ownership, age and argument
fields:</para>
<programlisting>Type Path Mode UID GID Age Argument
d /run/user 0755 root root 10d -
L /tmp/foobar - - - - /dev/null</programlisting>
<refsect2>
<title>Type</title>
<variablelist>
<varlistentry>
<term><varname>f</varname></term>
<listitem><para>Create a file if it doesn't exist yet (optionally writing a short string into it, if the argument parameter is passed)</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>F</varname></term>
<listitem><para>Create or truncate a file (optionally writing a short string into it, if the argument parameter is passed)</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>w</varname></term>
<listitem><para>Write the argument parameter to a file, if the file exists.
Lines of this type accept shell-style globs in place of normal path
names. The argument parameter will be written without a trailing
newline. C-style backslash escapes are interpreted.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>d</varname></term>
<listitem><para>Create a directory if it doesn't exist yet</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>D</varname></term>
<listitem><para>Create or empty a directory</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>p</varname></term>
<listitem><para>Create a named pipe (FIFO) if it doesn't exist yet</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>L</varname></term>
<listitem><para>Create a symlink if it doesn't exist yet</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>c</varname></term>
<listitem><para>Create a character device node if it doesn't exist yet</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>b</varname></term>
<listitem><para>Create a block device node if it doesn't exist yet</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>x</varname></term>
<listitem><para>Ignore a path
during cleaning. Use this type
to exclude paths from clean-up
as controlled with the Age
parameter. Note that lines of
this type do not influence the
effect of r or R lines. Lines
of this type accept
shell-style globs in place of
of normal path
names.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>r</varname></term>
<listitem><para>Remove a file
or directory if it
exists. This may not be used
to remove non-empty
directories, use R for
that. Lines of this type
accept shell-style globs in
place of normal path
names.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>R</varname></term>
<listitem><para>Recursively
remove a path and all its
subdirectories (if it is a
directory). Lines of this type
accept shell-style globs in
place of normal path
names.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>z</varname></term>
<listitem><para>Restore
SELinux security context label
and set ownership and access
mode of a file or directory if
it exists. Lines of this type
accept shell-style globs in
place of normal path names.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Z</varname></term>
<listitem><para>Recursively
restore SELinux security
context label and set
ownership and access mode of a
path and all its
subdirectories (if it is a
directory). Lines of this type
accept shell-style globs in
place of normal path
names.</para></listitem>
</varlistentry>
</variablelist>
</refsect2>
<refsect2>
<title>Mode</title>
<para>The file access mode to use when
creating this file or directory. If omitted or
when set to - the default is used: 0755 for
directories, 0644 for all other file
objects. For z, Z lines if omitted or when set
to - the file access mode will not be
modified. This parameter is ignored for x, r,
R, L lines.</para>
</refsect2>
<refsect2>
<title>UID, GID</title>
<para>The user and group to use for this file
or directory. This may either be a numeric
user/group ID or a user or group name. If
omitted or when set to - the default 0 (root)
is used. For z, Z lines when omitted or when set to -
the file ownership will not be modified.
These parameters are ignored for x, r, R, L lines.</para>
</refsect2>
<refsect2>
<title>Age</title>
<para>The date field, when set, is used to
decide what files to delete when cleaning. If
a file or directory is older than the current
time minus the age field it is deleted. The
field format is a series of integers each
followed by one of the following
postfixes for the respective time units:</para>
<variablelist>
<varlistentry>
<term><varname>s</varname></term>
<term><varname>min</varname></term>
<term><varname>h</varname></term>
<term><varname>d</varname></term>
<term><varname>w</varname></term>
<term><varname>ms</varname></term>
<term><varname>m</varname></term>
<term><varname>us</varname></term></varlistentry>
</variablelist>
<para>If multiple integers and units are specified the time
values are summed up.</para>
<para>The age field only applies to lines starting with
d, D and x. If omitted or set to - no automatic clean-up
is done.</para>
<para>If the age field starts with a tilde
character (~) the clean-up is only applied to
files and directories one level inside the
directory specified, but not the files and
directories immediately inside it.</para>
</refsect2>
<refsect2>
<title>Argument</title>
<para>For L lines determines the destination
path of the symlink. For c, b determines the
major/minor of the device node, with major and
minor formatted as integers, separated by :,
e.g. "1:3". For f, F, w may be used to specify
a short string that is written to the file,
suffixed by a newline. Ignored for all other
lines.</para>
</refsect2>
</refsect1>
<refsect1>
<title>Example</title>
<example>
<title>/etc/tmpfiles.d/screen.conf example</title>
<para><command>screen</command> needs two directories created at boot with specific modes and ownership.</para>
<programlisting>d /var/run/screens 1777 root root 10d
d /var/run/uscreens 0755 root root 10d12h</programlisting>
</example>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-tmpfiles</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-delta</refentrytitle><manvolnum>1</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>