path: root/en_US.ISO8859-1/books/handbook/users/chapter.sgml

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     The FreeBSD Documentation Project

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<chapter id="users">
  <chapterinfo>
    <authorgroup>
      <author>
        <firstname>Neil</firstname>
	<surname>Blakey-Milner</surname>
	<contrib>Contributed by </contrib>
      </author>
    </authorgroup>
    <!-- Feb 2000 -->
  </chapterinfo>

  <title>Users and Basic Account Management</title>
  
  <sect1 id="users-synopsis">
    <title>Synopsis</title>
    
    <para>FreeBSD allows multiple users to use the computer at the same time.
      Obviously, only one of those users can be sitting in front of the screen and
      keyboard at any one time
      <footnote>
	<para>Well, unless you hook up multiple terminals, but we will
	save that for <xref linkend="serialcomms">.</para>
      </footnote>, but any number of users can log in through the
      network to get their work done.  To use the system every user must have
      an account.</para>
    
    <para>After reading this chapter, you will know:</para>

    <itemizedlist>
      <listitem>
	<para>The differences between the various user accounts on a FreeBSD
	  system.</para>
      </listitem>

      <listitem>
	<para>How to add user accounts.</para>
      </listitem>

      <listitem>
	<para>How to remove user accounts.</para>
      </listitem>

      <listitem>
	<para>How to change account details, such as the user's full name, or
	preferred shell.</para>
      </listitem>

      <listitem>
	<para>How to set limits on a per-account basis, to control the
	  resources such as memory and CPU time that accounts and groups of
	  accounts are allowed to access.</para>
      </listitem>

      <listitem>
	<para>How to use groups to make account management easier.</para>
      </listitem>
    </itemizedlist>

    <para>Before reading this chapter, you should:</para>

    <itemizedlist>
      <listitem>
	<para>Understand the basics of &unix; and FreeBSD (<xref
	    linkend="basics">).</para>
      </listitem>
    </itemizedlist>
  </sect1>

  <sect1 id="users-introduction">
    <title>Introduction</title>

    <para>All access to the system is achieved via accounts, and all
      processes are run by users, so user and account management are
      of integral importance on FreeBSD systems.</para>

    <para>Every account on a FreeBSD system has certain information associated
      with it to identify the account.</para>

    <variablelist>
      <varlistentry>
	<term>User name</term>

	<listitem>
	  <para>The user name as it would be typed at the
	    <prompt>login:</prompt> prompt.  User names must be unique across
	    the computer; you may not have two users with the same
	    user name.  There are a number of rules for creating valid user
	    names, documented in &man.passwd.5;; you would typically use user
	    names that consist of eight or fewer all lower case
	    characters.</para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>Password</term>

	<listitem>
	  <para>Each account has a password associated with it.  The password
	    may be blank, in which case no password will be required to access
	    the system.  This is normally a very bad idea; every account
	    should have a password.</para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>User ID (UID)</term>

	<listitem>
	  <para>The UID is a number, traditionally from 0 to 65535<footnote id="users-largeuidgid">
	      <para>It is possible to use UID/GIDs as large as
		4294967295, but such IDs can cause serious problems
		with software that makes assumptions about the values
		of IDs.</para>
	    </footnote>, used to uniquely identify
	    the user to the system.  Internally, FreeBSD uses the UID to
	    identify users&mdash;any FreeBSD commands that allow you to
	    specify a user name will convert it to the UID before working with
	    it.  This means that you can have several accounts with different
	    user names but the same UID.  As far as FreeBSD is concerned these
	    accounts are one user.  It is unlikely you will ever need to do
	    this.</para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>Group ID (GID)</term>

	<listitem>
	  <para>The GID is a number, traditionally from 0 to 65535<footnoteref linkend="users-largeuidgid">, used to uniquely identify
	    the primary group that the user belongs to.  Groups are a
	    mechanism for controlling access to resources based on a user's
	    GID rather than their UID.  This can significantly reduce the size
	    of some configuration files.  A user may also be in more than one
	    group.</para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>Login class</term>

	<listitem>
	  <para>Login classes are an extension to the group mechanism that
	    provide additional flexibility when tailoring the system to
	    different users.</para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>Password change time</term>

	<listitem>
	  <para>By default FreeBSD does not force users to change their
	    passwords periodically.  You can enforce this on a per-user basis,
	    forcing some or all of your users to change their passwords after
	    a certain amount of time has elapsed.</para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>Account expiry time</term>

	<listitem>
	  <para>By default FreeBSD does not expire accounts.  If you are
	    creating accounts that you know have a limited lifespan, for
	    example, in a school where you have accounts for the students,
	    then you can specify when the account expires.  After the expiry
	    time has elapsed the account cannot be used to log in to the
	    system, although the account's directories and files will
	    remain.</para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>User's full name</term>

	<listitem>
	  <para>The user name uniquely identifies the account to FreeBSD, but
	    does not necessarily reflect the user's real name.  This
	    information can be associated with the account.</para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>Home directory</term>

	<listitem>
	  <para>The home directory is the full path to a directory on the
	    system in which the user will start when logging on to the
	    system.  A common convention is to put all user home directories
	    under
	    <filename>/home/<replaceable>username</replaceable></filename>
	    or <filename>/usr/home/<replaceable>username</replaceable></filename>.
	    The user would store their personal files in their home directory,
	    and any directories they may create in there.</para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>User shell</term>

	<listitem>
	  <para>The shell provides the default environment users use to
	    interact with the system.  There are many different kinds of
	    shells, and experienced users will have their own preferences,
	    which can be reflected in their account settings.</para>
	</listitem>
      </varlistentry>
    </variablelist>

    <para>There are three main types of accounts: the <link
	linkend="users-superuser">Superuser</link>, <link
	linkend="users-system">system users</link>, and <link
	linkend="users-user">user accounts</link>.  The Superuser
      account, usually called <username>root</username>, is used to
      manage the system with no limitations on privileges.  System
      users run services.  Finally, user accounts are used by real
      people, who log on, read mail, and so forth.</para>
  </sect1>
    
  <sect1 id="users-superuser">
    <title>The Superuser Account</title>
    
    <indexterm>
      <primary>accounts</primary>
      <secondary>superuser (root)</secondary>
    </indexterm>
    <para>The superuser account, usually called
      <username>root</username>, comes preconfigured to facilitate
      system administration, and should not be used for day-to-day
      tasks like sending and receiving mail, general exploration of
      the system, or programming.</para>
      
    <para>This is because the superuser, unlike normal user accounts,
      can operate without limits, and misuse of the superuser account
      may result in spectacular disasters.  User accounts are unable
      to destroy the system by mistake, so it is generally best to use
      normal user accounts whenever possible, unless you especially
      need the extra privilege.</para>

    <para>You should always double and triple-check commands you issue
      as the superuser, since an extra space or missing character can
      mean irreparable data loss.</para>

    <para>So, the first thing you should do after reading this
      chapter is to create an unprivileged user account for yourself
      for general usage if you have not already.  This applies equally
      whether you are running a multi-user or single-user machine.
      Later in this chapter, we discuss how to create additional
      accounts, and how to change between the normal user and
      superuser.</para>
  </sect1>
    
  <sect1 id="users-system">
    <title>System Accounts</title>

    <indexterm>
      <primary>accounts</primary>
      <secondary>system</secondary>
    </indexterm>
    <para>System users are those used to run services such as DNS,
      mail, web servers, and so forth.  The reason for this is
      security; if all services ran as the superuser, they could
      act without restriction.</para>

    <indexterm>
      <primary>accounts</primary>
      <secondary><username>daemon</username></secondary>
    </indexterm>
    <indexterm>
      <primary>accounts</primary>
      <secondary><username>operator</username></secondary>
    </indexterm>
    <para>Examples of system users are <username>daemon</username>,
      <username>operator</username>, <username>bind</username> (for
      the Domain Name Service), and <username>news</username>.  Often
      sysadmins create <username>httpd</username> to run web servers
      they install.</para>

    <indexterm>
      <primary>accounts</primary>
      <secondary><username>nobody</username></secondary>
    </indexterm>
    <para><username>nobody</username> is the generic unprivileged
      system user.  However, it is important to keep in mind that the
      more services that use <username>nobody</username>, the more
      files and processes that user will become associated with, and
      hence the more privileged that user becomes.</para>
  </sect1>

  <sect1 id="users-user">
    <title>User Accounts</title>

    <indexterm>
      <primary>accounts</primary>
      <secondary>user</secondary>
    </indexterm>
    <para>User accounts are the primary means of access for real
      people to the system, and these accounts insulate the user and
      the environment, preventing the users from damaging the system
      or other users, and allowing users to customize their
      environment without affecting others.</para>

    <para>Every person accessing your system should have a unique user
      account.  This allows you to find out who is doing what, prevent
      people from clobbering each others' settings or reading each
      others' mail, and so forth.</para>

    <para>Each user can set up their own environment to accommodate
      their use of the system, by using alternate shells, editors, key
      bindings, and language.</para>
  </sect1>

  <sect1 id="users-modifying">
    <title>Modifying Accounts</title>

    <indexterm>
      <primary>accounts</primary>
      <secondary>modifying</secondary>
    </indexterm>

    <para>There are a variety of different commands available in the
      &unix; environment to manipulate user accounts.  The most common
      commands are summarized below, followed by more detailed
      examples of their usage.</para>

    <informaltable>
      <tgroup cols="2">
	<thead>
	  <row>
	    <entry>Command</entry>
	    <entry>Summary</entry>
	  </row>
	</thead>
	<tbody>
	  <row>
	    <entry>&man.adduser.8;</entry>
	    <entry>The recommended command-line application for adding
	    new users.</entry>
	  </row>
	  <row>
	    <entry>&man.rmuser.8;</entry>
	    <entry>The recommended command-line application for
	    removing users.</entry>
	  </row>
	  <row>
	    <entry>&man.chpass.1;</entry>
	    <entry>A flexible tool to change user database information.</entry>
	  </row>
	  <row>
	    <entry>&man.passwd.1;</entry>
	    <entry>The simple command-line tool to change user
	    passwords.</entry>
	  </row>
	  <row>
	    <entry>&man.pw.8;</entry>
	    <entry>A powerful and flexible tool to modify all aspects
	    of user accounts.</entry>
	  </row>
	</tbody>
      </tgroup>
    </informaltable>

    <sect2 id="users-adduser">
      <title><command>adduser</command></title>

      <indexterm>
        <primary>accounts</primary>
        <secondary>adding</secondary>
      </indexterm>
      <indexterm>
        <primary><command>adduser</command></primary>
      </indexterm>
      <indexterm>
        <primary><filename class=directory>/usr/share/skel</filename></primary>
      </indexterm>
      <indexterm><primary>skeleton directory</primary></indexterm>
      <para>&man.adduser.8; is a simple program for
	adding new users.  It creates entries in the system
	<filename>passwd</filename> and <filename>group</filename>
	files.  It will also create a home directory for the new user,
	copy in the default configuration files (<quote>dotfiles</quote>) from
	<filename>/usr/share/skel</filename>, and can optionally mail
	the new user a welcome message.</para>

      <para>In &os;&nbsp;5.0, &man.adduser.8; was rewritten from a
	Perl script to a shell script that acts as wrapper around
	&man.pw.8;, so its usage is slightly different on &os;&nbsp;4.X
	and &os;&nbsp;5.X.</para>

      <para>To create the initial configuration file, use
	<command>adduser -s -config_create</command>.
	<footnote>
	  <para>The <option>-s</option> makes &man.adduser.8;
	    default to
	    quiet.  We use <option>-v</option> later when we want to
	    change defaults.</para>
	</footnote>
	Next, we configure &man.adduser.8;
	defaults, and create our first user account, since using
	<username>root</username> for normal usage is evil and
	nasty.</para>

      <example>
	<title>Configuring <command>adduser</command> and adding a
	  user on &os;&nbsp;4.X</title>

	<screen>&prompt.root; <userinput>adduser -v</userinput>
Use option ``-silent'' if you don't want to see all warnings and questions.
Check /etc/shells
Check /etc/master.passwd
Check /etc/group
Enter your default shell: csh date no sh tcsh zsh [sh]: <userinput>zsh</userinput>
Your default shell is: zsh -&gt; /usr/local/bin/zsh
Enter your default HOME partition: [/home]:
Copy dotfiles from: /usr/share/skel no [/usr/share/skel]: 
Send message from file: /etc/adduser.message no 
[/etc/adduser.message]: <userinput>no</userinput>
Do not send message
Use passwords (y/n) [y]: <userinput>y</userinput>

Write your changes to /etc/adduser.conf? (y/n) [n]: <userinput>y</userinput>

Ok, let's go.
Don't worry about mistakes. I will give you the chance later to correct any input.
Enter username [a-z0-9_-]: <userinput>jru</userinput>
Enter full name []: <userinput>J. Random User</userinput>
Enter shell csh date no sh tcsh zsh [zsh]: 
Enter home directory (full path) [/home/jru]: 
Uid [1001]: 
Enter login class: default []: 
Login group jru [jru]: 
Login group is ``jru''. Invite jru into other groups: guest no 
[no]: <userinput>wheel</userinput>
Enter password []: 
Enter password again []: 

Name:	  jru
Password: ****
Fullname: J. Random User
Uid:	  1001
Gid:	  1001 (jru)
Class:	  
Groups:	  jru wheel
HOME:     /home/jru
Shell:	  /usr/local/bin/zsh
OK? (y/n) [y]: <userinput>y</userinput>
Added user ``jru''
Copy files from /usr/share/skel to /home/jru
Add another user? (y/n) [y]: <userinput>n</userinput>
Goodbye!
&prompt.root;</screen>
      </example>

      <para>In summary, we changed the default shell to
	<application>zsh</application> (an additional shell found in
	the Ports Collection), and turned off the sending of a welcome mail to
	added users.  We then saved the configuration,
	created an account for <username>jru</username>, and made
	sure <username>jru</username> is in <username>wheel</username>
	group (so that she may assume the role of
	<username>root</username> with the &man.su.1;
	command.)</para>

      <note>
	<para>The password you type in is not echoed, nor are asterisks
	  displayed.  Make sure you do not mistype the password twice.
	  </para>
      </note>

      <note>
	<para>Just use &man.adduser.8; without arguments
	  from now on, and you will not have to go through changing the
	  defaults.  If the program asks you to change the defaults,
	  exit the program, and try the <option>-s</option>
	  option.</para>
      </note>

      <example>
	<title>Adding a user on &os;&nbsp;5.X</title>

	<screen>&prompt.root; <userinput>adduser</userinput>
Username: <userinput>jru</userinput>
Full name: <userinput>J. Random User</userinput>
Uid (Leave empty for default):
Login group [jru]:
Login group is jru. Invite jru into other groups? []: <userinput>wheel</userinput>
Login class [default]:
Shell (sh csh tcsh zsh nologin) [sh]: <userinput>zsh</userinput>
Home directory [/home/jru]:
Use password-based authentication? [yes]:
Use an empty password? (yes/no) [no]:
Use a random password? (yes/no) [no]:
Enter password:
Enter password again:
Lock out the account after creation? [no]:
Username   : jru
Password   : ****
Full Name  : J. Random User
Uid        : 1001
Class      :
Groups     : jru wheel
Home       : /home/jru
Shell      : /usr/local/bin/zsh
Locked     : no
OK? (yes/no): <userinput>yes</userinput>
adduser: INFO: Successfully added (jru) to the user database.
Add another user? (yes/no): <userinput>no</userinput>
Goodbye!
&prompt.root;</screen>
      </example>
    </sect2>

    <sect2 id="users-rmuser">
      <title><command>rmuser</command></title>

      <indexterm><primary><command>rmuser</command></primary></indexterm>
      <indexterm>
        <primary>accounts</primary>
        <secondary>removing</secondary>
      </indexterm>

      <para>You can use &man.rmuser.8; to
	completely remove a user from the system.
	&man.rmuser.8; performs the following
	steps:</para>

      <procedure>
	<step>
	  <para>Removes the user's &man.crontab.1; entry (if
	    any).</para>
	</step>
	<step>
	  <para>Removes any &man.at.1; jobs belonging to the
	    user.</para>
	</step>
	<step>
	  <para>Kills all processes owned by the user.</para>
	</step>
	<step>
	  <para>Removes the user from the system's local password
	    file.</para>
	</step>
	<step>
	  <para>Removes the user's home directory (if it is owned by
	    the user).</para>
	</step>
	<step>
	  <para>Removes the incoming mail files belonging to the user
	    from <filename>/var/mail</filename>.</para>
	</step>
	<step>
	  <para>Removes all files owned by the user from temporary
	    file storage areas such as <filename>/tmp</filename>.</para>
	</step>
	<step>
	  <para>Finally, removes the username from all groups to which
	    it belongs in <filename>/etc/group</filename>.
	    
	    <note>
	      <para>If a group becomes empty and the group name is the
		same as the username, the group is removed; this
		complements the per-user unique groups created by
		&man.adduser.8;.</para>
	    </note>
	  </para>
	</step>
      </procedure>

      <para>&man.rmuser.8; cannot be used to remove
	superuser accounts, since that is almost always an indication
	of massive destruction.</para>

      <para>By default, an interactive mode is used, which attempts to
	make sure you know what you are doing.</para>

      <example>
	<title><command>rmuser</command> Interactive Account Removal</title>

	<screen>&prompt.root; <userinput>rmuser jru</userinput>
Matching password entry:
jru:*:1001:1001::0:0:J. Random User:/home/jru:/usr/local/bin/zsh
Is this the entry you wish to remove? <userinput>y</userinput>
Remove user's home directory (/home/jru)? <userinput>y</userinput>
Updating password file, updating databases, done.
Updating group file: trusted (removing group jru -- personal group is empty) done.
Removing user's incoming mail file /var/mail/jru: done.
Removing files belonging to jru from /tmp: done.
Removing files belonging to jru from /var/tmp: done.
Removing files belonging to jru from /var/tmp/vi.recover: done.
&prompt.root;</screen>
      </example>
    </sect2>

    <sect2 id="users-chpass">
      <title><command>chpass</command></title>

      <indexterm><primary><command>chpass</command></primary></indexterm>
      <para>&man.chpass.1; changes user database
	information such as passwords, shells, and personal
	information.</para>

      <para>Only system administrators, as the superuser, may change
	other users' information and passwords with 
	&man.chpass.1;.</para>

      <para>When passed no options, aside from an optional username,
	&man.chpass.1; displays an editor
	containing user information.  When the user exists from the
	editor, the user database is updated with the new
	information.</para>

      <note>
	<para>In &os;&nbsp;5.X, you will be asked for your password
	 after exiting the editor if you are not the superuser.</para>
      </note>

      <example>
	<title>Interactive <command>chpass</command> by Superuser</title>

	<screen>#Changing user database information for jru.
Login: jru
Password: *
Uid [#]: 1001
Gid [# or name]: 1001
Change [month day year]:
Expire [month day year]:
Class:
Home directory: /home/jru
Shell: /usr/local/bin/zsh
Full Name: J. Random User
Office Location:
Office Phone:
Home Phone:
Other information:</screen>
      </example>

      <para>The normal user can change only a small subset of this
	information, and only for themselves.</para>

      <example>
	<title>Interactive <command>chpass</command> by Normal User</title>

	<screen>#Changing user database information for jru.
Shell: /usr/local/bin/zsh
Full Name: J. Random User
Office Location:
Office Phone:
Home Phone:
Other information:</screen>
      </example>

      <note>
	<para>&man.chfn.1; and &man.chsh.1; are
	  just links to &man.chpass.1;, as 
	  are &man.ypchpass.1;,
	  &man.ypchfn.1;, and
	  &man.ypchsh.1;.  NIS support is automatic, so
	  specifying the <literal>yp</literal> before the command is
	  not necessary.  If this is confusing to you, do not worry, NIS will
	  be covered in <xref linkend="advanced-networking">.</para>
      </note>
    </sect2>
    <sect2 id="users-passwd">
      <title><command>passwd</command></title>

      <indexterm><primary><command>passwd</command></primary></indexterm>
      <indexterm>
        <primary>accounts</primary>
        <secondary>changing password</secondary>
      </indexterm>
      <para>&man.passwd.1; is the usual way to
	change your own password as a user, or another user's password
	as the superuser.</para>

      <note>
	<para>Users must type in their original password before
	  changing their password, to prevent an unauthorized person
	  from changing their password when the user is away from
	  their console.</para>
      </note>

      <example>
	<title>Changing Your Password</title>

	<screen>&prompt.user; <userinput>passwd</userinput>
Changing local password for jru.
Old password:
New password:
Retype new password:
passwd: updating the database...
passwd: done</screen>
      </example>

      <example>
	<title>Changing Another User's Password as the Superuser</title>

        <screen>&prompt.root; <userinput>passwd jru</userinput>
Changing local password for jru.
New password:
Retype new password:
passwd: updating the database...
passwd: done</screen>
      </example>

      <note>
	<para>As with &man.chpass.1;,
	  &man.yppasswd.1; is just a link to
	  &man.passwd.1;, so NIS works with either
	  command.</para>
      </note>
    </sect2>


    <sect2 id="users-pw">
      <title><command>pw</command></title>
      <indexterm><primary><command>pw</command></primary></indexterm>

      <para>&man.pw.8; is a command line utility to create, remove,
	modify, and display users and groups.  It functions as a front
	end to the system user and group files.  &man.pw.8;
	has a very powerful set of command line options that make it
	suitable for use in shell scripts, but new users may find it
	more complicated than the other commands presented
	here.</para>
    </sect2>


  </sect1>

  <sect1 id="users-limiting">
    <title>Limiting Users</title>

    <indexterm><primary>limiting users</primary></indexterm>
    <indexterm>
      <primary>accounts</primary>
      <secondary>limiting</secondary>
    </indexterm>
    <para>If you have users, the ability to limit their system use may
      have come to mind.  FreeBSD provides
      several ways an administrator can limit the amount of system
      resources an individual may use.  These limits are
      divided into two sections: disk quotas, and other resource
      limits.</para>

    <indexterm><primary>quotas</primary></indexterm>
    <indexterm>
      <primary>limiting users</primary>
      <secondary>quotas</secondary>
    </indexterm>
    <indexterm><primary>disk quotas</primary></indexterm>
    <para>Disk quotas limit disk usage to users, and
      they
      provide a way to quickly check that usage without
      calculating it every time.  Quotas are discussed in <xref
      linkend="quotas">.</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>

    <indexterm>
      <primary><filename>/etc/login.conf</filename></primary>
    </indexterm>
    <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 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
      <literal><replaceable>name</replaceable>=<replaceable>value</replaceable></literal>
      pair, where <replaceable>name</replaceable> is a well-known
      identifier and <replaceable>value</replaceable> 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>
    <indexterm><primary>coredumpsize</primary></indexterm>
    <indexterm>
      <primary>limiting users</primary>
      <secondary>coredumpsize</secondary>
    </indexterm>
	  <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., <application>emacs</application>) crash.</para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>cputime</literal></term>

	<listitem>
    <indexterm><primary>cputime</primary></indexterm>
    <indexterm>
      <primary>limiting users</primary>
      <secondary>cputime</secondary>
    </indexterm>
	  <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&mdash;probably a
	        legitimate task&mdash;can easily use almost 100% of a CPU
	        for some time.</para>
	    </note>
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>filesize</literal></term>

	<listitem>
    <indexterm><primary>filesize</primary></indexterm>
    <indexterm>
      <primary>limiting users</primary>
      <secondary>filesize</secondary>
    </indexterm>
	  <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>
    <indexterm><primary>maxproc</primary></indexterm>
        <indexterm>
      <primary>limiting users</primary>
      <secondary>maxproc</secondary>
    </indexterm>
	  <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 <varname>kern.maxproc</varname>
	    &man.sysctl.8;.  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
	    preprocessors).</para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>memorylocked</literal></term>

	<listitem>
    <indexterm><primary>memorylocked</primary></indexterm>
    <indexterm>
      <primary>limiting users</primary>
      <secondary>memorylocked</secondary>
    </indexterm>
	  <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;, lock into main memory such that in the event
	    of being swapped out, they do not contribute to
	    a system's trashing in time of trouble.</para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>memoryuse</literal></term>

	<listitem>
    <indexterm><primary>memoryuse</primary></indexterm>
    <indexterm>
      <primary>limiting users</primary>
      <secondary>memoryuse</secondary>
    </indexterm>
	  <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>
    <indexterm><primary>openfiles</primary></indexterm>
    <indexterm>
      <primary>limiting users</primary>
      <secondary>openfiles</secondary>
    </indexterm>
	  <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
	    <varname>kern.maxfiles</varname> &man.sysctl.8;.</para>
	</listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>sbsize</literal></term>

	<listitem>
    <indexterm><primary>sbsize</primary></indexterm>
    <indexterm>
      <primary>limiting users</primary>
      <secondary>sbsize</secondary>
    </indexterm>
	  <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>
    <indexterm><primary>stacksize</primary></indexterm>
    <indexterm>
      <primary>limiting users</primary>
      <secondary>stacksize</secondary>
    </indexterm>
	  <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 
	  <varname>openfiles</varname> 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,
      character sets, date and time standards, and so on.  This is
      discussed in the <link linkend="l10n">localization</link>
      chapter.</para>
  </sect1>

  <sect1 id="users-groups">
    <title>Groups</title>

    <indexterm><primary>groups</primary></indexterm>
    <indexterm>
      <primary><filename>/etc/groups</filename></primary>
    </indexterm>
    <indexterm>
      <primary>accounts</primary>
      <secondary>groups</secondary>
    </indexterm>
    <para>A group is simply a list of users.  Groups are identified by
      their group name and GID (Group ID).  In FreeBSD (and most other &unix; like
      systems), the two factors the kernel uses to decide whether a process
      is allowed to do something is its user ID and list of groups it
      belongs to.  Unlike a user ID, a process has a list of groups
      associated with it.  You may hear some things refer to the <quote>group ID</quote>
      of a user or process; most of the time, this just means the first
      group in the list.</para>

    <para>The group name to group ID map is in
      <filename>/etc/group</filename>.  This is a plain text file with four
      colon-delimited fields.  The first field is the group name, the
      second is the encrypted password, the third the group ID, and the
      fourth the comma-delimited list of members.  It can safely be edited
      by hand (assuming, of course, that you do not make any syntax
      errors!).  For a more complete description of the syntax, see the
      &man.group.5; manual page.</para>

    <para>If you do not want to edit <filename>/etc/group</filename>
      manually, you can use the &man.pw.8; command to add and edit groups.
      For example, to add a group called <groupname>teamtwo</groupname> and
      then confirm that it exists you can use:</para>

    <example>
      <title>Adding a Group Using &man.pw.8;</title>

      <screen>&prompt.root; <userinput>pw groupadd teamtwo</userinput>
&prompt.root; <userinput>pw groupshow teamtwo</userinput>
teamtwo:*:1100:</screen>
    </example>

    <para>The number <literal>1100</literal> above is the group ID of the
      group <groupname>teamtwo</groupname>.  Right now,
      <groupname>teamtwo</groupname> has no members, and is thus rather
      useless.  Let's change that by inviting <username>jru</username> to
      the <groupname>teamtwo</groupname> group.</para>

    <example>
      <title>Adding Somebody to a Group Using &man.pw.8;</title>

      <screen>&prompt.root; <userinput>pw groupmod teamtwo -M jru</userinput>
&prompt.root; <userinput>pw groupshow teamtwo</userinput>
teamtwo:*:1100:jru</screen>
    </example>

    <para>The argument to the <option>-M</option> option is a
      comma-delimited list of users who are members of the group.  From the
      preceding sections, we know that the password file also contains a
      group for each user.  The latter (the user) is automatically added to
      the group list by the system; the user will not show up as a member
      when using the <option>groupshow</option> command to &man.pw.8;,
      but will show up when the information is queried via &man.id.1; or
      similar tool.  In other words, &man.pw.8; only manipulates the
      <filename>/etc/group</filename> file; it will never attempt to read
      additionally data from <filename>/etc/passwd</filename>.</para>

    <example>
      <title>Using &man.id.1; to Determine Group Membership</title>

      <screen>&prompt.user; <userinput>id jru</userinput>
uid=1001(jru) gid=1001(jru) groups=1001(jru), 1100(teamtwo)</screen>
    </example>

    <para>As you can see, <username>jru</username> is a member of the
      groups <groupname>jru</groupname> and
      <groupname>teamtwo</groupname>.</para>

    <para>For more information about &man.pw.8;, see its manual page, and
      for more information on the format of
      <filename>/etc/group</filename>, consult the &man.group.5; manual
      page.</para>
  </sect1>
</chapter>

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