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man: clarify that user rlimits cannot go beyond limits set for service mgr

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Fixes: #10758
This commit is contained in:
Lennart Poettering 2020-01-16 19:22:30 +01:00
parent 59d83463d1
commit 54ed193f8d
2 changed files with 45 additions and 52 deletions
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32
man/systemd-system.conf.xml
View File

@ -382,30 +382,14 @@
<term><varname>DefaultLimitRTPRIO=</varname></term>
<term><varname>DefaultLimitRTTIME=</varname></term>
<listitem><para>These settings control various default
resource limits for units. See
<citerefentry><refentrytitle>setrlimit</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for details. The resource limit is possible to specify in two formats,
<option>value</option> to set soft and hard limits to the same value,
or <option>soft:hard</option> to set both limits individually (e.g. DefaultLimitAS=4G:16G).
Use the string <varname>infinity</varname> to
configure no limit on a specific resource. The multiplicative
suffixes K (=1024), M (=1024*1024) and so on for G, T, P and E
may be used for resource limits measured in bytes
(e.g. DefaultLimitAS=16G). For the limits referring to time values,
the usual time units ms, s, min, h and so on may be used (see
<citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for details). Note that if no time unit is specified for
<varname>DefaultLimitCPU=</varname> the default unit of seconds is
implied, while for <varname>DefaultLimitRTTIME=</varname> the default
unit of microseconds is implied. Also, note that the effective
granularity of the limits might influence their
enforcement. For example, time limits specified for
<varname>DefaultLimitCPU=</varname> will be rounded up implicitly to
multiples of 1s. These settings may be overridden in individual units
using the corresponding LimitXXX= directives. Note that these resource
limits are only defaults for units, they are not applied to PID 1
itself.</para></listitem>
<listitem><para>These settings control various default resource limits for processes executed by
units. See
<citerefentry><refentrytitle>setrlimit</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
details. These settings may be overridden in individual units using the corresponding
<varname>LimitXXX=</varname> directives, see
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>, for
details, and they accept the same parameter syntax. Note that these resource limits are only defaults
for units, they are not applied to the service manager process (i.e. PID 1) itself.</para></listitem>
</varlistentry>
<varlistentry>

65
man/systemd.exec.xml
View File

@ -498,42 +498,51 @@ CapabilityBoundingSet=~CAP_B CAP_C</programlisting>
<term><varname>LimitRTTIME=</varname></term>
<listitem><para>Set soft and hard limits on various resources for executed processes. See
<citerefentry><refentrytitle>setrlimit</refentrytitle><manvolnum>2</manvolnum></citerefentry> for details on
the resource limit concept. Resource limits may be specified in two formats: either as single value to set a
specific soft and hard limit to the same value, or as colon-separated pair <option>soft:hard</option> to set
both limits individually (e.g. <literal>LimitAS=4G:16G</literal>). Use the string <option>infinity</option> to
configure no limit on a specific resource. The multiplicative suffixes K, M, G, T, P and E (to the base 1024)
may be used for resource limits measured in bytes (e.g. LimitAS=16G). For the limits referring to time values,
the usual time units ms, s, min, h and so on may be used (see
<citerefentry><refentrytitle>setrlimit</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
details on the resource limit concept. Resource limits may be specified in two formats: either as
single value to set a specific soft and hard limit to the same value, or as colon-separated pair
<option>soft:hard</option> to set both limits individually (e.g. <literal>LimitAS=4G:16G</literal>).
Use the string <option>infinity</option> to configure no limit on a specific resource. The
multiplicative suffixes K, M, G, T, P and E (to the base 1024) may be used for resource limits
measured in bytes (e.g. <literal>LimitAS=16G</literal>). For the limits referring to time values, the
usual time units ms, s, min, h and so on may be used (see
<citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
details). Note that if no time unit is specified for <varname>LimitCPU=</varname> the default unit of seconds
is implied, while for <varname>LimitRTTIME=</varname> the default unit of microseconds is implied. Also, note
that the effective granularity of the limits might influence their enforcement. For example, time limits
specified for <varname>LimitCPU=</varname> will be rounded up implicitly to multiples of 1s. For
<varname>LimitNICE=</varname> the value may be specified in two syntaxes: if prefixed with <literal>+</literal>
or <literal>-</literal>, the value is understood as regular Linux nice value in the range -20..19. If not
prefixed like this the value is understood as raw resource limit parameter in the range 0..40 (with 0 being
equivalent to 1).</para>
details). Note that if no time unit is specified for <varname>LimitCPU=</varname> the default unit of
seconds is implied, while for <varname>LimitRTTIME=</varname> the default unit of microseconds is
implied. Also, note that the effective granularity of the limits might influence their
enforcement. For example, time limits specified for <varname>LimitCPU=</varname> will be rounded up
implicitly to multiples of 1s. For <varname>LimitNICE=</varname> the value may be specified in two
syntaxes: if prefixed with <literal>+</literal> or <literal>-</literal>, the value is understood as
regular Linux nice value in the range -20..19. If not prefixed like this the value is understood as
raw resource limit parameter in the range 0..40 (with 0 being equivalent to 1).</para>
<para>Note that most process resource limits configured with these options are per-process, and processes may
fork in order to acquire a new set of resources that are accounted independently of the original process, and
may thus escape limits set. Also note that <varname>LimitRSS=</varname> is not implemented on Linux, and
setting it has no effect. Often it is advisable to prefer the resource controls listed in
<para>Note that most process resource limits configured with these options are per-process, and
processes may fork in order to acquire a new set of resources that are accounted independently of the
original process, and may thus escape limits set. Also note that <varname>LimitRSS=</varname> is not
implemented on Linux, and setting it has no effect. Often it is advisable to prefer the resource
controls listed in
<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>
over these per-process limits, as they apply to services as a whole, may be altered dynamically at runtime, and
are generally more expressive. For example, <varname>MemoryLimit=</varname> is a more powerful (and working)
replacement for <varname>LimitRSS=</varname>.</para>
<para>For system units these resource limits may be chosen freely. For user units however (i.e. units run by a
per-user instance of
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>), these limits are
bound by (possibly more restrictive) per-user limits enforced by the OS.</para>
over these per-process limits, as they apply to services as a whole, may be altered dynamically at
runtime, and are generally more expressive. For example, <varname>MemoryMax=</varname> is a more
powerful (and working) replacement for <varname>LimitRSS=</varname>.</para>
<para>Resource limits not configured explicitly for a unit default to the value configured in the various
<varname>DefaultLimitCPU=</varname>, <varname>DefaultLimitFSIZE=</varname>, … options available in
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, and –
if not configured there – the kernel or per-user defaults, as defined by the OS (the latter only for user
services, see above).</para>
services, see below).</para>
<para>For system units these resource limits may be chosen freely. When these settings are configured
in a user service (i.e. a service run by the per-user instance of the service manager) they cannot be
used to raise the limits above those set for the user manager itself when it was first invoked, as
the user's service manager generally lacks the privileges to do so. In user context these
configuration options are hence only useful to lower the limits passed in or to raise the soft limit
to the maximum of the hard limit as configured for the user. To raise the user's limits further, the
available configuration mechanisms differ between operating systems, but typically require
privileges. In most cases it is possible to configure higher per-user resource limits via PAM or by
setting limits on the system service encapsulating the user's service manager, i.e. the user's
instance of <filename>user@.service</filename>. After making such changes, make sure to restart the
user's service manager.</para>
<table>
<title>Resource limit directives, their equivalent <command>ulimit</command> shell commands and the unit used</title>