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<refentry id= "file-hierarchy" >
<refentryinfo >
<title > file-hierarchy</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 > file-hierarchy</refentrytitle>
<manvolnum > 7</manvolnum>
</refmeta>
<refnamediv >
<refname > file-hierarchy</refname>
<refpurpose > File system hierarchy overview</refpurpose>
</refnamediv>
<refsect1 >
<title > Description</title>
<para > Operating systems using the
<citerefentry > <refentrytitle > systemd</refentrytitle> <manvolnum > 1</manvolnum> </citerefentry>
system and service manager are organized based on a
file system hierarchy inspired by UNIX, more
specificaly the hierarchy described in the <ulink
url="http://refspecs.linuxfoundation.org/FHS_2.3/fhs-2.3.html">File
System Hierarchy</ulink> specification and
<citerefentry > <refentrytitle > hier</refentrytitle> <manvolnum > 7</manvolnum> </citerefentry> . This
manual page describes a more minimal, modernized
subset of these specifications that defines more
strictly the suggestions and restrictions systemd
makes on the file system hierarchy.</para>
</refsect1>
<refsect1 >
<title > General Structure</title>
<variablelist >
<varlistentry >
<term > <filename > /</filename> </term>
<listitem > <para > The file system
root. Usually writable, but this is
not required. Possibly a temporary
file system (<literal > tmpfs</literal> ). Not shared with
other hosts (unless read-only). The
administrator may create additional
top-level subdirectories in this tree,
if required and the name does not
conflict with any of the directories
listed below.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /boot</filename> </term>
<listitem > <para > The boot partition
used for bringing up the system. On
EFI systems this is possibly the EFI
System Partition, also see
<citerefentry > <refentrytitle > systemd-boot-generator</refentrytitle> <manvolnum > 8</manvolnum> </citerefentry> . This
directory is usually strictly local
the host, and should be considered
read-only, except when a new kernel or
boot loader is installed. This
directory only exists on systems that
run on physical or emulated hardware
that requires boot
loaders.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /etc</filename> </term>
<listitem > <para > System-specific
configuration. This directory may or
may not be read-only. Frequently, this
directory is pre-populated with
vendor-supplied configuration files,
but applications should not make
assumptions about this directory
being fully populated or populated at
all, and should fall back to defaults
if configuration is missing.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /home</filename> </term>
<listitem > <para > The location for
normal user's home
directories. Possibly shared with
other systems, and never
read-only. This directory should only
be used for normal users, never for
system users. This directory and
possibly the directories contained
within it might only become available
or writable in late boot or even on
user login only. This directory might
be placed on limited-functionality
network file systems, hence
applications should not assume the
full set of file API is available on
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this directory. Applications should
generally not reference this directory
directly, but via the per-user
<varname > $HOME</varname> environment
variable, or via the home directory
field of the user
database.</para> </listitem>
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</varlistentry>
<varlistentry >
<term > <filename > /root</filename> </term>
<listitem > <para > The home directory of
the root user. The root user's home
directory is located outside of
<filename > /home</filename> in order to
make sure the root user may log in
even without <filename > /home</filename>
being available and
mounted.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /srv</filename> </term>
<listitem > <para > The place to store
general server payload, managed by the
administrator. No restrictions are
made how this directory is organized
internally. Generally writable, and
possibly shared among systems. This
directory might become available or
writable only very late during
boot.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /tmp</filename> </term>
<listitem > <para > The place for small
temporary files. This directory is
usually mounted as
<literal > tmpfs</literal> instance, and
should hence not be used for larger
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files. (Use
<filename > /var/tmp</filename> for
larger files.) Since the directory is
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accessible to other users of the
system it is essential that this
directory is only written to with the
<citerefentry > <refentrytitle > mkstemp</refentrytitle> <manvolnum > 3</manvolnum> </citerefentry> ,
<citerefentry > <refentrytitle > mkdtemp</refentrytitle> <manvolnum > 3</manvolnum> </citerefentry>
and related calls. This directory is
usually flushed at boot-up. Also,
files that are not accessed within a
certain time are usually automatically
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deleted. If applications find the
environment variable
<varname > $TMP</varname> set they
should prefer using the directory
specified in it over directly
referencing
<filename > /tmp</filename> .</para> </listitem>
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</varlistentry>
</variablelist>
</refsect1>
<refsect1 >
<title > Runtime Data</title>
<variablelist >
<varlistentry >
<term > <filename > /run</filename> </term>
<listitem > <para > A
<literal > tmpfs</literal> file system
for system packages to place runtime
data in. This directory is flushed on
boot, and generally writable for
priviliged programs
only. Always writable.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /run/log</filename> </term>
<listitem > <para > Runtime system
logs. System components may place
private logs in this directory. Always
writable, even when
<filename > /var/log</filename> might
not be accessible
yet.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /run/user</filename> </term>
<listitem > <para > Contains per-user
runtime directories, each usually
invidually mounted
<literal > tmpfs</literal>
instances. Always writable, flushed at
each reboot and when the user logs
out. User code should not reference
this directory directly, but via the
<varname > $XDG_RUNTIME_DIR</varname>
environment variable, as documented in
the <ulink
url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
Base Directory
Specification</ulink> .</para> </listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 >
<title > Vendor-supplied Operating System Resources</title>
<variablelist >
<varlistentry >
<term > <filename > /usr</filename> </term>
<listitem > <para > Vendor-supplied
operating system resources. Usually
read-only, but this is not
required. Possibly shared between
multiple hosts. This directory should
not be modified by the administrator,
except when installing or removing
vendor-supplied
packages.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /usr/bin</filename> </term>
<listitem > <para > Binaries for user
commands, that shall appear in the
<varname > $PATH</varname> search
path. It is recommended not to place
binaries in this directory that are
not useful for invocation from a shell
(such as daemon binaries); these
should be placed in a subdirectory of
<filename > /usr/lib</filename>
instead.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /usr/include</filename> </term>
<listitem > <para > C and C++ API header
files of system
libraries.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /usr/lib</filename> </term>
<listitem > <para > System libraries and
package-specific
data.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /usr/lib64</filename> </term>
<listitem > <para > Secondary library
directory for placing 64bit versions
of system libraries in, if the primary
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architecture of the system is 32bit,
and <filename > /usr/lib64</filename> is
defined in the platform ABI. This
directory should not be used for
package-specific data, unless this
data requires 64bit-specific versions,
too.</para> </listitem>
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</varlistentry>
<varlistentry >
<term > <filename > /usr/share</filename> </term>
<listitem > <para > Resources shared
betwen multiple packages, such as
documentation, man pages, time zone
information, fonts and other
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resources. Usually, the precise
location and format of files stored
below this directory is subject to
specifications that ensure
interoperability.</para> </listitem>
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</varlistentry>
<varlistentry >
<term > <filename > /usr/share/doc</filename> </term>
<listitem > <para > Documentation for the
operating system or system
packages.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /usr/share/factory/etc</filename> </term>
<listitem > <para > Repository for
vendor-supplied default configuration
files. This directory should be
populated with pristine vendor versions
of all configuration files that may be
placed in
<filename > /etc</filename> . This is
useful to compare the local
configuration of a system with vendor
defaults and to populate the local
configuration with
defaults.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /usr/share/factory/var</filename> </term>
<listitem > <para > Similar to
<filename > /usr/share/factory/etc</filename>
but for vendor versions of files in
the variable, persistent data
directory
<filename > /var</filename> .</para> </listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 >
<title > Persistent Variable System Data</title>
<variablelist >
<varlistentry >
<term > <filename > /var</filename> </term>
<listitem > <para > Persistent, variable
system data. Must be writable. This
directory might be pre-populated with
vendor-supplied data, but applications
should be able to reconstruct
necessary files and directories in
this subhierarchy should they be
missing, as the system might start up
without this directory being
populated. Persistency is recommended,
but optional, to support ephemeral
systems. This directory might become
available or writable only very late
during boot. Components that are
required to operate during early boot
hence shall not unconditionally rely
on this directory.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /var/cache</filename> </term>
<listitem > <para > Persistent system
cache data. System components may
place non-essential data in this
directory. Flushing this directory
should have no effect on operation of
programs, except for increased
runtimes necessary to rebuild these
caches.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /var/lib</filename> </term>
<listitem > <para > Persistent system
data. System components may
place private data in this
directory.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /var/log</filename> </term>
<listitem > <para > Persistent system
logs. System components may place
private logs in this directory, though
it is recommended to do most logging
via the
<citerefentry > <refentrytitle > syslog</refentrytitle> <manvolnum > 3</manvolnum> </citerefentry>
and
<citerefentry > <refentrytitle > sd_journal_print</refentrytitle> <manvolnum > 3</manvolnum> </citerefentry>
calls.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /var/spool</filename> </term>
<listitem > <para > Persistent system
spool data, such as printer or mail
queues.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /var/tmp</filename> </term>
<listitem > <para > The place for larger
and persistent temporary files. In
contrast to <filename > /tmp</filename>
this directory is usually mounted from
a persistent physical file system and
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can thus accept larger files. (Use
<filename > /tmp</filename> for smaller
files.) This directory is generally
not flushed at boot-up, but time-based
cleanup of files that have not been
accessed for a certain time is
applied. The same security
restrictions as with
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<filename > /tmp</filename> apply, and
hence only
<citerefentry > <refentrytitle > mkstemp</refentrytitle> <manvolnum > 3</manvolnum> </citerefentry> ,
<citerefentry > <refentrytitle > mkdtemp</refentrytitle> <manvolnum > 3</manvolnum> </citerefentry>
or similar calls should be used to
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make use of this directory. If
applications find the environment
variable <varname > $TMP</varname> set
they should prefer using the directory
specified in it over directly
referencing
<filename > /var/tmp</filename> .
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</para> </listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 >
<title > Virtual Kernel and API File Systems</title>
<variablelist >
<varlistentry >
<term > <filename > /dev</filename> </term>
<listitem > <para > The root directory for
device nodes. Usually this directory
is mounted as
<literal > devtmpfs</literal> instance,
but might be of a different type in
sandboxed/containerized setups. This
directory is managed jointly by the
kernel and
<citerefentry > <refentrytitle > systemd-udevd</refentrytitle> <manvolnum > 8</manvolnum> </citerefentry> ,
and should not be written to by other
components. A number of special
purpose virtual file systems might be
mounted below this
directory.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /dev/shm</filename> </term>
<listitem > <para > Place for POSIX shared
memory segments, as created via
<citerefentry > <refentrytitle > shm_open</refentrytitle> <manvolnum > 3</manvolnum> </citerefentry> . This
directory is flushed on boot, and is a
<literal > tmpfs</literal> file
system. Since all users have write
access to this directory, special care
should be taken to avoid name clashes
and vulnerabilities. For normal users,
shared memory segments in this
directory are usually deleted when the
user logs out. Usually it is a better
idea to use memory mapped files in
<filename > /run</filename> (for system
programs) or
<varname > $XDG_RUNTIME_DIR</varname>
(for user programs) instead of POSIX
shared memory segments, since they
directories are not world-writable and
hence not vulnerable to
security-sensitive name
clashes.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /proc</filename> </term>
<listitem > <para > A virtual kernel file
system exposing the process list and
other functionality. This file system
is mostly an API to interface with the
kernel and not a place where normal
files may be stored. For details, see
<citerefentry > <refentrytitle > proc</refentrytitle> <manvolnum > 5</manvolnum> </citerefentry> . A
number of special purpose virtual file
systems might be mounted below this
directory.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /proc/sys</filename> </term>
<listitem > <para > A hierarchy below
<filename > /proc</filename> that
exposes a number of kernel
tunables. The primary way to configure
the settings in this API file tree is
via
<citerefentry > <refentrytitle > sysctl.d</refentrytitle> <manvolnum > 5</manvolnum> </citerefentry>
files. In sandboxed/containerized
setups this directory is generally
mounted read-only.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /sys</filename> </term>
<listitem > <para > A virtual kernel file
system exposing discovered devices and
other functionality. This file system
is mostly an API to interface with the
kernel and not a place where normal
files may be stored. In
sandboxed/containerized setups this
directory is generally mounted
read-only. A number of special purpose
virtual file systems might be mounted
below this
directory.</para> </listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 >
<title > Compatibility Symlinks</title>
<variablelist >
<varlistentry >
<term > <filename > /bin</filename> </term>
<term > <filename > /sbin</filename> </term>
<term > <filename > /usr/sbin</filename> </term>
<listitem > <para > These compatibility
symlinks point to
<filename > /usr/bin</filename> ,
ensuring that scripts and binaries
referencing these legacy paths
correctly find their binaries.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /lib</filename> </term>
<listitem > <para > This compatibility
symlink points to
<filename > /usr/lib</filename> ,
ensuring that binaries referencing
this legacy path correctly find
their libraries.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /lib64</filename> </term>
<listitem > <para > This compatibility
symlink points to
<filename > /usr/lib64</filename> ,
ensuring that binaries referencing
this legacy path correctly find their
libraries. This symlink only exists on
architectures whose ABI requires a
64bit version of the library
directory.</para> </listitem>
</varlistentry>
<varlistentry >
<term > <filename > /var/run</filename> </term>
<listitem > <para > This compatibility
symlink points to
<filename > /run</filename> , ensuring
that programs referencing this legacy
path correctly find their runtime
data.</para> </listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 >
<title > System Packages</title>
<para > Developers of system packages should follow
strict rules when placing their own files in the file
system. The following table lists recommended
locations for specific types of files.</para>
<table >
<title > System Package Data Location</title>
<tgroup cols= '2' align= 'left' colsep= '1' rowsep= '1' >
<colspec colname= "directory" />
<colspec colname= "purpose" />
<thead >
<row >
<entry > Directory</entry>
<entry > Purpose</entry>
</row>
</thead>
<tbody >
<row >
<entry > <filename > /usr/bin</filename> </entry>
<entry > Package executables that shall appear in the <varname > $PATH</varname> executable search path. It is not recommended to place internal binaries or binaries that are not commonly invoked from the shell in this directory, such as daemon binaries. As this directory is shared with most other packages of the system special care should be take to pick unique names for files placed here, that are unlikely to clash with other package's files.</entry>
</row>
<row >
<entry > <filename > /usr/lib</filename> </entry>
<entry > Public shared libraries of the package, compiled for the primary architecture of the operating system. As above, be careful with using too generic names, and pick unique names for your libraries to place here to avoid name clashes.</entry>
</row>
<row >
<entry > <filename > /usr/lib/<replaceable > package</replaceable> </filename> </entry>
<entry > Private other vendor resources of the package, including private binaries and libraries, but also including any other kind of read-only vendor data.</entry>
</row>
<row >
<entry > <filename > /usr/lib64</filename> </entry>
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<entry > Public shared libraries of the package, compiled for the secondary, 64bit architecture, if this is part of the platform ABI of the architecture.</entry>
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</row>
<row >
<entry > <filename > /usr/lib64/<replaceable > package</replaceable> </filename> </entry>
<entry > Private other vendor resources of the package that are architecture-specific and cannot be shared between primary and secondary architectures. Note that this generally does not include private binaries since binaries of the primary architecture may generally be invoked from secondary architecture code just fine.</entry>
</row>
<row >
<entry > <filename > /usr/include/<replaceable > package</replaceable> </filename> </entry>
<entry > Public C/C++ APIs of public shared libraries of the package.</entry>
</row>
<row >
<entry > <filename > /etc/<replaceable > package</replaceable> </filename> </entry>
<entry > System-specific configuration for the package. It is recommended to default to safe fallbacks if this configuration is missing, if this is possible. Alternatively, a <citerefentry > <refentrytitle > tmpfiles.d</refentrytitle> <manvolnum > 5</manvolnum> </citerefentry> fragment may be used to copy or symlink the necessary files and directores from <filename > /usr/share/factory</filename> during boot, via the <literal > L</literal> or <literal > C</literal> directives.</entry>
</row>
<row >
<entry > <filename > /run/<replaceable > package</replaceable> </filename> </entry>
<entry > Runtime data for the package. Packages must be able to create the necessary subdirectories in this tree on their own, since the directory is flushed automatically on boot. Alternatively, a <citerefentry > <refentrytitle > tmpfiles.d</refentrytitle> <manvolnum > 5</manvolnum> </citerefentry> fragment may be used to create the necessary directories during boot.</entry>
</row>
<row >
<entry > <filename > /run/log/<replaceable > package</replaceable> </filename> </entry>
<entry > Runtime log data for the package.</entry>
</row>
<row >
<entry > <filename > /var/cache/<replaceable > package</replaceable> </filename> </entry>
<entry > Persistent cache data of the package. If this directory is flushed the application should work correctly on next invocation, though possibly slowed done due to the need to rebuild any local cache files.</entry>
</row>
<row >
<entry > <filename > /var/lib/<replaceable > package</replaceable> </filename> </entry>
<entry > Persistent private data of the package. This is the primary place to put persistent data that does not fall into the other categories listed. Packages should be able to create the necessary subdirectories in this tree on their own, since the directory might be missing on boot. Alternatively, a <citerefentry > <refentrytitle > tmpfiles.d</refentrytitle> <manvolnum > 5</manvolnum> </citerefentry> fragment may be used to create the necessary directories during boot.</entry>
</row>
<row >
<entry > <filename > /var/log/<replaceable > package</replaceable> </filename> </entry>
<entry > Persistent log data of the package.</entry>
</row>
<row >
<entry > <filename > /var/spool/<replaceable > package</replaceable> </filename> </entry>
<entry > Persistent spool/queue data of the package.</entry>
</row>
</tbody>
</tgroup>
</table>
</refsect1>
<refsect1 >
<title > See Also</title>
<para >
<citerefentry > <refentrytitle > systemd</refentrytitle> <manvolnum > 1</manvolnum> </citerefentry> ,
<citerefentry > <refentrytitle > hier</refentrytitle> <manvolnum > 7</manvolnum> </citerefentry> ,
<citerefentry > <refentrytitle > systemd-boot-generator</refentrytitle> <manvolnum > 8</manvolnum> </citerefentry> ,
<citerefentry > <refentrytitle > sysctl.d</refentrytitle> <manvolnum > 5</manvolnum> </citerefentry> ,
</para>
</refsect1>
</refentry>
