Date: Tue, 17 Apr 2001 00:16:55 -0700 From: Dima Dorfman <dima@unixfreak.org> To: doc@freebsd.org Subject: Update Users chapter of Handbook (request for review) Message-ID: <20010417071655.B1A9D3E28@bazooka.unixfreak.org>
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I've written an update to the Users chapter of the Handbook to talk
about resource limits. As far as I know, the latter isn't documented
anywhere except login.conf(5), and that's not very new-user-friendly.
This lack of documentation often manifests itself as "FreeBSD is
vulnerable to fork-bombing" on -questions.
Attached is a patch that separates the "limiting and personalizing
users" part of the Users chapter into "limiting users", which talks
about resource limits (new), and "personalizing users", which just has
a link to the localization chapter (old).
Comments and suggestions welcome.
Thanks in advance,
Dima Dorfman
dima@unixfreak.org
Index: chapter.sgml
===================================================================
RCS file: /st/src/FreeBSD/doc/en_US.ISO_8859-1/books/handbook/users/chapter.sgml,v
retrieving revision 1.5
diff -u -r1.5 chapter.sgml
--- chapter.sgml 2001/01/20 03:35:19 1.5
+++ chapter.sgml 2001/04/17 07:12:17
@@ -397,13 +397,222 @@
</sect2>
</sect1>
- <sect1 id="users-limiting-and-personalizing">
- <title>Limiting and Personalizing Users</title>
+ <sect1 id="users-limiting">
+ <title>Limiting Users</title>
- <para>Quotas allow the system administrator to set disk usage
- maximums, and users to check their disk usage, if quotas are
- used on the system. Quotas are discussed in their <link
- linkend="quotas">own chapter</link>.</para>
+ <para>If you run a multi-user system, chances are that you do not trust
+ all of your users not to damage your system. FreeBSD provides a
+ number of ways a system administrator can limit the amount of system
+ resources an individual user can use. These limits are generally
+ divided into two sections: disk quotas, and other resources
+ limits.</para>
+
+ <para>Disk quotas are a way for the system administrator to tell the
+ filesystem the amount of disk space a user may use; moreover, they
+ provide a way to quickly check on the disk usage of a user without
+ having to calculate it every time. Quotas are discussed in <link
+ linkend="quotas">their own section</link> of the <link
+ linkend="disks">Disks</link> chapter.</para>
+
+ <para>The other resource limits include ways to limit the amount of
+ CPU, memory, and other resources a user may consume. These are
+ defined using login classes and are discussed here.</para>
+
+ <para>Login classes are defined in
+ <filename>/etc/login.conf</filename>. The precise semantics are
+ beyond the scope of this section, but are described in detail in the
+ &man.login.conf.5; manual page. It is sufficient to say that each
+ user can is assigned to a login class (<literal>default</literal> by
+ default), and that each login class has a set of login capabilities
+ associated with it. A login capability is a
+ <quote>name=value</quote> pair, where <quote>name</quote> is a
+ well-known identifier and <quote>value</quote> is an arbitrary string
+ processed accordingly depending on the name. Setting up login
+ classes and capabilities is rather straight-forward, and is also
+ described in &man.login.conf.5;.</para>
+
+ <para>Resource limits are different from plain vanilla login
+ capabilities in two ways. First, for every limit, there is a soft
+ (current) and hard limit. A soft limit may be adjusted by the user
+ or application, but may be no higher than the hard limit. The latter
+ may be lowered by the user, but never raised. Second, most resource
+ limits apply per process to a specific user, not the user as a whole.
+ Note, however, that these differences are mandated by the specific
+ handling of the limits, not by the implementation of the login
+ capability framework (i.e., they are not <emphasis>really</emphasis>
+ a special case of login capabilities).</para>
+
+ <para>And so, without further ado, below are the most commonly used
+ resource limits (the rest, along with all the other login
+ capabilities, may be found in &man.login.conf.5;).</para>
+
+ <variablelist>
+ <varlistentry>
+ <term><literal>coredumpsize</literal></term>
+
+ <listitem>
+ <para>The limit on the size of a core file generated by a program
+ is, for obvious reasons, subordinate to other limits on disk
+ usage (e.g., <literal>filesize</literal>, or disk quotas).
+ Nevertheless, it is often used as a less-severe method of
+ controlling disk space consumption: since users do not generate
+ core files themselves, and often do not delete them, setting this
+ may save them from running out of disk space should a large
+ program (e.g., Emacs) crash.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>cputime</literal></term>
+
+ <listitem>
+ <para>This is the maximum amount of CPU time a user's process may
+ consume. Offending processes will be killed by the kernel.
+
+ <note>
+ <para>This is a limit on CPU <emphasis>time</emphasis>
+ consumed, not percentage of the CPU as displayed in some
+ fields by &man.top.1; and &man.ps.1;. A limit on the
+ latter is, at the time of this writing, not possible, and
+ would be rather useless: a compiler—probably a
+ legitimate task—can easily use almost 100% of a CPU
+ for some time.</para>
+ </note>
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>filesize</literal></term>
+
+ <listitem>
+ <para>This is the maximum size of a file the user may possess.
+ Unlike <link linkend="quotas">disk quotas</link>, this limit is
+ enforced on individual files, not the set of all files a user
+ owns.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>maxproc</literal></term>
+
+ <listitem>
+ <para>This is the maximum number of processes a user may be
+ running. This includes foreground and background processes
+ alike. For obvious reasons, this may not be larger than the
+ system limit specified by the <literal>kern.maxproc</literal>
+ sysctl. Also note that setting this too small may hinder a
+ user's productivity: it is often useful to be logged in
+ multiple times or execute pipelines. Some tasks, such as
+ compiling a large program, also spawn multiple processes (e.g.,
+ &man.make.1;, &man.cc.1;, and other intermediate
+ preproccesors).</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>memorylocked</literal></term>
+
+ <listitem>
+ <para>This is the maximum amount a memory a process may have
+ requested to be locked into main memory (e.g., see
+ &man.mlock.2;). Some system-critical programs, such as
+ &man.amd.8;, do this so that their getting swapped out does not
+ contribute to a system's thrashing in time of trouble.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>memoryuse</literal></term>
+
+ <listitem>
+ <para>This is the maximum amount of memory a process may consume
+ at any given time. It includes both core memory and swap
+ usage. This is not a catch-all limit for restricting memory
+ consumption, but it is a good start.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>openfiles</literal></term>
+
+ <listitem>
+ <para>This is the maximum amount of files a process may have
+ open. In FreeBSD, files are also used to represent sockets and
+ IPC channels; thus, be careful not to set this too low. The
+ system-wide limit for this is defined by the
+ <literal>kern.maxfiles</literal> sysctl.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>sbsize</literal></term>
+
+ <listitem>
+ <para>This is the limit on the amount of network memory, and thus
+ mbufs, a user may consume. This originated as a response to an
+ old DoS attack by creating a lot of sockets, but can be
+ generally used to limit network communications.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>stacksize</literal></term>
+
+ <listitem>
+ <para>This is the maximum size a process' stack may grow to.
+ This alone is not sufficient to limit the amount of memory a
+ program may use; consequently, it should be used in conjunction
+ with other limits.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+
+ <para>There are a few other things to remember when setting resource
+ limits. Following are some general tips, suggestions, and
+ miscellaneous comments.</para>
+
+ <itemizedlist>
+ <listitem>
+ <para>Processes started at system startup by
+ <filename>/etc/rc</filename> are assigned to the
+ <literal>daemon</literal> login class.</para>
+ </listitem>
+
+ <listitem>
+ <para>Although the <filename>/etc/login.conf</filename> that comes
+ with the system is a good source of reasonable values for most
+ limits, only you, the administrator, can know what is appropriate
+ for your system. Setting a limit too high may open your system
+ up to abuse, while setting it too low may put a strain on
+ productivity.</para>
+ </listitem>
+
+ <listitem>
+ <para>Users of the X Window System (X11) should probably be granted
+ more resources than other users. X11 by itself takes a lot of
+ resources, but it also encourages users to run more programs
+ simultaneously.</para>
+ </listitem>
+
+ <listitem>
+ <para>Remember that many limits apply to individual processes, not
+ the user as a whole. For example, setting openfiles to 50 means
+ that each process the user runs may open up to 50 files. Thus,
+ the gross amount of files a user may open is the value of
+ <literal>openfiles</literal> multiplied by the value of
+ <literal>maxproc</literal>. This also applies to memory
+ consumption.</para>
+ </listitem>
+ </itemizedlist>
+
+ <para>For further information on resource limits and login classes and
+ capabilities in general, please consult the relevant manual pages:
+ &man.cap.mkdb.1;, &man.getrlimit.2;, &man.login.conf.5;.</para>
+ </sect1>
+
+ <sect1 id="users-personalizing">
+ <title>Personalizing Users</title>
<para>Localization is an environment set up by the system
administrator or user to accommodate different languages,
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